1
Q
What is a pathogen?
A
An organism that causes disease
2
Q
Define commensal. What is it also called?
A
- An organism that colonises the host but causes no disease under normal circumstances
- Also called colonisation
3
Q
What is an opportunist pathogen?
A
A microbe that only causes disease if the host defence is compromised
4
Q
Define virulence/pathogenicity.
A
The degree to which an organism is pathogenic
5
Q
What are the categories for describing bacteria?
A
- Gram +ve or gram -ve
- Shape: cocci (circular) or bacilli (rods)
- Cocci can be individual, clusters or chains
- Bacilli can be chains, curved or spiral rods
6
Q
What do we mean by gram positive and gram negative bacteria? What colours do these stain? Which dyes are responsible for these colours?
A
- Gram positive: has a thick layer of peptidoglycan, stains PURPLE. This is because it is stained by crystal violet
- Gram negative: has a thin layer of peptidoglycan (high lipid content), stains PINK. This is because it is stained by safranin
7
Q
What are the stages for the gram staining method?
A
Mnemonic: Come In And Stain = Crystal violet, Iodine, Alcohol, Safranin
- Fixation of clinical materials to microscope slide (heat/methanol)
- Application of crystal violet. Wash off excess
- Application of iodine. Wash off excess
- Decolorisation step: use acetone or ethanol, this will distinguish between gram +ve and -ve bacteria. This is because gram +ve will be purple + rest will decolourise
- Application of safranin to stain gram -ve pink
8
Q
What type of organism would you stain with Ziehl-Neelsen stain?
A
Used to identify acid-fast (resist decolorisation by acids during staining procedures) organisms, mainly mycobacteria, e.g. TB
9
Q
What types of bacteria release endotoxin?
A
Gram negative bacteria. An example of endotoxins are lipopolysaccharides
10
Q
What types of bacteria release exotoxins?
A
Gram positive and gram negative bacteria
11
Q
What can gram positive cocci be split into? Which test can be used to distinguish between these?
A
- Gram +ve cocci can be split into staphylococcus (clusters) and streptococcus (chains)
- A CATALASE test can be used - this detects the presence of catalase enzyme using hydrogen peroxide (H2O2 + staphylococci = gas bubbles)
- +ve catalase test = staphylococcus, -ve catalase test = streptococcus
12
Q
Which test can be performed to distinguish between staphylococci? What do positive and negative tests indicate?
A
- COAGULASE test. This looks at whether a fibrin clot is produced
- Coagulase +ve = staphylococcus aureus. This is because it produces coagulase that converts soluble fibrinogen to insoluble fibrin
- Coagulase -ve = all others (staphylococci epidermis, staphylococcus saprophyticus)
13
Q
Which test can we perform to distinguish between streptococci?
A
Blood agar haemolytic. Blood agar can undergo 3 types of haemolysis depending on the organism: beta haemolysis = complete lysis (clear area), alpha haemolysis = partial lysis (green), gamma haemolysis = none
14
Q
If alpha haemolysis is shown after haemolysis in blood agar, which test do we perform to differentiate? What do positive and negative results indicate?
A
- OPTOCHIN test
- Optochin +ve = STREPTOCOCCUS PNEUMONIAE (clear demarcated ring around optochin disc)
- Optochin -ve = streptococcus viridans
15
Q
What is the appearance of strep pneumoniae under a microscope?
A
Gram positive diplococci
16
Q
If beta haemolysis is shown after haemolysis on blood agar, which test is performed? What do the different groups indicate?
A
- LANCEFIELD TEST. This groups bacteria based on the carbohydrate composition of the bacterial antigen on their cell wall. Groups into A, B, C, D and G
- A: streptococcus pyogenes
- B: streptococcus agalactiae
- G: streptococcus dysgalactiae
17
Q
If gamma haemolysis is shown after haemolysis on blood agar, which test is performed? What do the results indicate?
A
- Lancefield test
- D: streptococcus bovis, enterococcus
18
Q
How does the haemolysis test work?
A
The haemolysis test uses hydrogen peroxide to test the reaction with haemoglobin
19
Q
Useful table that summarises gram positive cocci. But learn microbiology by the condition, not the organism.
A
20
Q
List some important gram positive bacilli.
A
- Listeria monocytogenes
- Propionibacterium acne - acne
- Clostridium difficile - diarrhoea from antibiotic overuse
21
Q
What kind of bacteria is MacConkey agar used with? What does it contain? How does it work?
A
- MacConkey agar is used to differentiate gram negative bacilli
- MacConkey agar contains bile salts, lactose and neutral red (pH indicator)
- Identifies bacteria that can ferment lactose
- Ferment lactose -> produce acid -> pH drop < 6.8 = pink, pH>6.8 = normal colour
22
Q
What can gram negative bacilli be split into? What is the appearance on MacConkey agar?
A
- Lactose fermenting and non-lactose fermenting
- Lactose fermenting = pink: E. coli, klebsiella
- Non-lactose fermenting = colourless/yellow: shigella, salmonella, pseudomonas, proteus
23
Q
What is XLD agar used for?
A
It is a very selective growth medium used to isolate salmonella and shigella. Salmonella shows black dots.
24
Q
The MacConkey agar appears yellow. Which test can be performed to decide which gram negative bacilli it is?
A
- OXIDASE test. This is used to determine if a bacterium produces certain Cytochrome C oxidases
- Positive result = black/purple = pseudomonas or neisseria (this is a COCCI and not a BACCILI)
- Negative result = colourless = shigella, salmonella, proteus
25
How do we know whether the positive result is pseudomona or neisseria?
Anti-pseudomonas sensitivity tests
26
How do we know if the negative result on the MacConkey agar is proteus or not?
The UREASE test. This would be positive if the gram negative bacilli was proteus mirabilis
27
Give 4 virulence factors of staphylococci.
1. Toxins
2. Proteases
3. Toxic Shock Syndrome Toxin
4. Protein A
28
Does salmonella have an H antigen?
Salmonella is motile and has a flagellum, therefore has an H antigen
29
Does E.coli have an H antigen?
E.coli is motile and has a flagellum, therefore has an H antigen
30
Whihc type of E.coli would you associate with causing traveller's diarrhoea?
Enterotoxigenic E.coli (ETEC)
31
What are the symptoms of enteropathogenic E.coli infection?
Chronic watery diarrhoea
32
What are the symptoms of enterohaemorrhagic E.coli infection?
Bloody diarrhoea
33
What are the symptoms of shigella infection?
Severe bloody diarrhoea and frequent passage
34
What bacteria is responsible for salmonellosis?
S.enterica
35
What are some gram negative cocci?
Neisseria meningitidis, moraxella cartarrhalis
36
How does any neisseria appear under a microscope?
Gram negative diplococci
37
What is a comma/curbed shaped gram negative bacteria?
Vibrio cholera - rice water stool
38
Give examples of helical shaped gram negative bacteria.
- Campylobacter jejuni - bloody diarrhoea
- Helicobacter pylori - gastric and duodenal ulcer
39
Give an example of a coccobacilli.
Haemophilus influenza
40
What does haemophilus influenza require to grow?
Haemophilus influenza is a gram negative coccobacilli + requires factor X and V to grow
41
What is fastidious bacteria? In order to be able to grow, what does it require?
- Fastidious bacteria has complex or particular nutritional requirements
- It requires chocolate agar (which is blood agar but with lysed RBCs due to heating to 80 degrees Celsius)
42
What does neisseria meningitidis require to grow?
Chocolate agar as it requires haem and NAD
43
Useful table for gram negative bacteria.
44
What are the uses of these agar:
a) Blood
b) Chocolate
c) MacConkey
d) CLED
e) XLD agar?
45
How would you grow haemophilus influenzae?
On chocolate agar as it requires haem and NAD
46
What diseases can haemophilus influenzae cause?
Meningitis and pneumonia
47
What are mycobacteria? Give examples.
- Aerobic, non-spore forming, non-mobile bacilli
- Slow-growing causes gradual onset of disease
- Requires multi-antibiotic treatment for a prolonged period
- 2 main examples = TB + leprosy
48
Where can we get bovine TB from?
We can get bovine TB from m. bovis from cows
49
What is mycobacteria cultured with?
Mycobacteria take a long time to culture, so have to be cultured with Löwenstein-Jensen medium
50
Which stain is required to stain mycobacteria? Why?
- Ziehl-Neelsen stain is used to identify acid-fast bacilli
- This is because the mycolic acid in the cell wall does not absorb normal gram stain
51
Describe the process of Ziehl-Neelsen staining.
TOP EXAM QUESTION:
- Z-N staining involves HEATING the sample with CARBOL FUSCHIN (strong dye)
- Heat makes the bacteria resistant to decolourisation by acid = acid-fast (ACID-FASTNESS is a property of all Mycobacterium)
- So when the slide is then flooded with acid, Mycobacteria retain the pink dye. Meanwhile everything else is decolourised to blue
52
Are viruses self-dependent?
No, they rely on the host cells for living - they have no organelles or cell walls
53
What are some ways that viruses cause disease?
- Direct destruction (polio)
- Modification (rotavirus)
- Over-reactivity of the immune system (hepatitis B)
- Damage through cell proliferation (HPV)
- Evasion of host cell defences (VZV)
54
Do viruses have a cell wall?
NO! Viruses have an outer protein coat that is sometimes surrounded by a lipid envelope but they do not have a cell wall
55
What are the 6 stages of viral replication?
1. Attachment.
2. Cell entry.
3. Interaction with host cell.
4. Replication.
5. Assembly.
6. Release.
56
How do viruses attach to a host cell?
Viruses have proteins on their surface that interact with receptors on host cell membranes
57
What part of the virus will enter the host cell?
Only the viral core carrying the nucleic acids will enter the host cell cytoplasm. Sometimes proteins that act as enzymes may enter too
58
How do viruses interact with host cells?
Viruses use cell materials, e.g. enzymes, amino acids and nucleotides, for their replication and they evade host defence mechanisms
59
Where in a cell does viral replication occur?
In the nucleus, cytoplasm or both
60
How can viruses be released from a cell?
1. Bursting open; lysis of cell.
2. 'Leaking' from the cell over a period of time; exocytosis
61
What are the 5 ways by which viruses can cause disease?
1. Damage by direct destruction: cell lysis
2. Damage by modification of cell structure
3. 'Over-reactivity' of the host as a response to infection: immuno-pathological damage
4. Damage via cell proliferation and immortalisation
5. Evasion of host defences
62
How can we detect viruses?
- Not visible in light microscopy, can't culture as only reproduce inside live cells
- PCR + nucleic acid amplification tests (NAAT) used, also can do serology (look for antibodies in response to virus)
63
What can qPCR detect?
1. The presence or absence of DNA/RNA
2. It can quantify the level of virus in a tissue
64
What virus can cause shingles?
Varicella Zoster Virus
65
What are the 3 groups of worms/helminths?
1. Nematodes (roundworms)
2. Trematodes (flatworms)
3. Cestodes (tapeworms)
66
Define pre-patent period.
Pre-patent period = the interval between infection and appearance of eggs/larvae in the stool
67
Which immunoglobulins are mainly involved with worms?
IgG and IgE
68
What is hookworm the leading cause of? What are the clinical features of hookworm? What is the treatment for hookworm?
- Hookworm is the leading cause of iron-deficiency anaemia
- Clinical features: ground itch (papules at the site of entry, e.g. on feet) + pulmonary symptoms
- Treatment: normally mebendazole
69
Which helminth is very common in the UK, usually affects whole households and causes an itchy bum?
Enterobius vermicularis
70
What symptoms does Wucheria bancroftii cause?
Filiriasis causing lymphoedema
71
What does Schistosomiasis cause?
Squamous cell bladder cancer
72
What are protozoa?
Microscopic unicellular eukaryotes
73
Protozoa are classified based on what? What are the 5 categories of protozoa?
- Protozoa are classified based on their movement
- 5 types:
1. Flagellates
2. Amoebae
3. Sporozoa
4. Ciliates
5. Microsporidia
74
What is giardiasis caused by? What are the symptoms? How is it treated?
- Giardiasis is caused by giardia
- Diarrhoea due to the alteration of intestinal villi, reducing absorption
- Treatment: metronidazole
75
What are the symptoms of Entmoeba histolytica? What is the treatment?
- Bloody diarrhoea, liver abcess
- Treatment: metronidazole
76
How is malaria transmitted?
Malaria is transmitted by the bite of a FEMALE ANOPHELES mosquito. The mosquito carries plasmodium (5 types)
77
What are the 5 species of malaria?
1. Plasmodium falciparum (most important)
2. Plasmodium ovale
3. Plasmodium vivax
4. Plasmodium malariae
5. Plasmodium knowlesi
78
What are the signs and symptoms of malaria?
- Signs: anaemia, jaundice, hepatosplenomegaly, 'Black Water Fever'
- Symptoms: FEVER, chills, headache, myalgia, fatigue, diarrhoea, vomiting, abdominal pain
79
What are the stages of the plasmodia life cycle in the human called?
Exo-erythrocytic and endo-erythrocytic stages
80
Describe the life cycle of malaria.
1. Infected mosquito injects parasite (sporozoite) when it bites human
2. Sporozoites travel to liver via blood and take up residence in hepatocytes
3. In the liver, the sporozoites multiply and become merozoites. The hepatocytes then burst, releasing it into the blood
4. In the blood, these merozoites invade erythrocytes and multiply again until the cell bursts
5. The cycle repeats itself, the merozoites invade RBCs and multiply and then burst out. This causes chills, fever and sweating
6. After several asexual cycles, merozoites can invade RBCs + instead of replicating, they develop into sexual form of the parasite (gametocytes)
7. Mosquito bites the infected human. It digests the gametocytes which will allows it to develop into mature sex cells (gametes)
8. Male and female gametes enter sporogenic cycle producing more pathogenic sporozoites
9. Mosquito (female) can infect another human causing malaria
81
What 2 species of the plasmodia genus lie dormant and cause late relapse of malaria?
P.ovale and P.vivax
82
What is the treatment for malaria?
- Uncomplicated malaria:
- ORAL CHLOROQUINE
- QUININE SULPHATE
- DOXYCYCLINE
- Severe or complicated malaria:
- IV ARTESUNATE. This is the most effective treatment but is not licensed
- QUININE DIHYDROCHLORIDE
83
What is an antibiotic?
Antibiotics are molecules that work by binding to a target site on a bacteria
84
What varies with antibiotic class?
The binding site will vary with antibiotic class
85
What are the two groups of antibiotics that inhibit cell wall synthesis?
- Beta lactams
- Glycopeptides
86
What are the categories of beta lactam antibiotics? Name the important antibiotics within these categories.
- Penicillins: Flucloxacillin, Amoxicillin/Ampicillin, Benzylpenicillin (Penicillin G), Penicillin V, Pipericillin
- Cephalosporins: Cefuroxime, Cefotaxime, Ceftriaxone
- Carbapenems: Meropenem
87
What are the glycopeptides we need to know?
Glycopeptides: vancomycin, teicoplanin
88
What are beta lactams effective against?
Gram positive bacteria (because they inhibit cell wall synthesis + gram positive have a large cell wall)
89
What is the mechanism of beta lactams?
- They disrupt peptidoglycan production by irreversibly binding to Pencillin Binding Proteins (PBPs)
- Cell wall is disrupted and lysis occurs. This results in a hypo-osmotic or iso-osmotic environment
90
In order to bind to the PBPs, what must beta lactams first diffuse through? Which bacteria are usually more susceptible to beta lactams? Why?
- To bind to the PBPs, the β-lactam antibiotic must first diffuse through the bacterial cell wall
- Gram-positive usually more susceptible to β-lactams than gram-negative bacteria. Gram-negative organisms have an additional lipopolysaccharide layer that decreases antibiotic penetration
91
Why do beta lactams differ in their activity? Are they effective at treating intracellular pathogens? Why?
- Due to their relative affinity for different PBPs
- Because the penicillins poorly penetrate mammalian cells, they are ineffective in the treatment of intracellular pathogens
92
Name a few antibiotics that inhibit nucleic acid synthesis.
- DNA strand breaks: Metronidazole (Nitroidimazoles)
- Inhibit DNA gyrase: Ciprofloxacin, Levofloxacin (Fluoroquinolones)
- Binds to RNA polymerase: Rifampicin
93
Name a few antibiotics that inhibit protein synthesis.
- Aminoglycosides: Gentamycin, Streptomycin
- Tetracyclines: Tetracycline, Doxycycline
- Macrolides: Clarythromycin, Erythromycin
- Chloraphemnicol
94
Name a couple of antibiotics that inhibit folate synthesis.
- Trimethoprim
- Sulfonamides: Sulphamethoxazole
- Co-trimaxazole (Trimethoprim and Sulphamethoxazole)
95
What do bacteriocidal antibiotics do?
They kill the bacteria, e.g. antibiotics that inhibit cell wall synthesis
96
What do bacteriostatic antibiotics do?
They prevent the growth of bacteria - 'inhibitory to growth', e.g. antibiotics that inhibit protein synthesis, DNA replication or metabolism
97
Name 6 sterile sites in the body.
1. Urinary tract.
2. CSF.
3. Pleural fluid.
4. Peritoneal cavity.
5. Blood.
6. Lower respiratory tract.
98
Where in the body would you find normal flora (commensals)?
1. Mouth.
2. Skin.
3. Vagina.
4. Urethra.
5. Large intestine.
99
What is the Minimum Inhibitory Concentration (MIC)?
The MIC is the lowest concentration of a chemical that prevents growth of a bacterium
100
Does the lowest MIC mean the best antibiotic?
No. There are many other important factors that need to be considered, e.g. the number of binding sites occupied and how long they're being occupied for
101
What is the MBC:MIC ratio for bacteriostatic antibiotics?
Bacteriostatic antibiotics are defined as having a Minimum Bactericidal Concentration (MBC): Minimum Inhibitory Concentration (MIC) ratio \>4
102
What are the two major determinants of anti-bacterial effects?
- The concentration and time that the antibiotic remains on these binding sites
- Time dependent killing: the time that serum concentrations remain above the MIC = t\>MIC
- How high the concentration is above the MIC =
103
Which group of antibiotics do we generally use for those with a penicillin allergy?
Macrolides, e.g. Clarithromycin, Erythromycin
104
Which antibiotic should we never give to pregnant women? Why?
Trimethoprim. This is because it is a folate synthesis inhibitor. Folate is important during pregnancy to prevent spina bifida
105
What are the 4 ways in which bacteria resist antibiotics?
- Change antibiotic target
- Destroy antibiotic
- Prevent antibiotic abcess
- Remove antibiotic from bacteria
106
How do bacteria change the antibiotic target? Give examples.
- Bacteria changes the molecular configuration of antibiotic binding site or masks it, e.g.
1. Flucloxacillin (or methicillin) is no longer able to bind PBP of Staphylococci – MRSA
2. Wall components change in enterococci and reduce vancomycin binding – VRE
3. Rifampicin activity reduced by changes to RNA polymerase in MTB – MDR-TB
107
Give examples of when bacteria destroy the antibiotic.
Beta lactam ring of Penicillins and Cephalosporins hydrolysed by bacterial enzyme ‘Beta lactamase’ = unable to bind PBP
108
How do some bacteria prevent antibiotic abcess? Give an example.
They modify the bacterial membrane porin channel size, numbers and selectivity, e.g. gram negative bacteria against aminoglycosides
109
How do some bacteria remove antibiotic from themselves? Give an example.
Proteins in bacterial membranes act as an export or efflux pumps - so level of antibiotic is reduced, e.g. S. aureus or S. pneumoniae resistance to fluoroquinolones
110
What are the two types of bacterial resistance?
- Intrinsic
- Acquired
111
What is intrinsic resistance? Give a couple of examples.
- Naturally occuring, all subpopulations of a species will be equally resistant:
## Footnote
- Aerobic bacteria are unable to reduce metronidazole to its active form
- Vancomycin cannot penetrate outer membrane of gram negative bacteria
112
What is acquired resistance in bacteria? Name the two types.
- A bacterium which was previously susceptible obtains the ability to resist the activity of a particular antibiotic. Only certain strains or subpopulations of a species will be resistant
- Two types: spontaneous gene mutation and horizontal gene transfer
113
What happens in a spontaneous gene mutation?
New nucleotide base pair, change in amino acid sequence, change to enzyme or cell structure, reduced affinity or activity of the antibiotic
114
What are the three types of horizontal gene transfer?
- Conjugation = sharing of extra chromosomal bacterial plasmids
- Transduction - insertion of DNA by bacteriophages
- Transformation = picking up naked DNA
115
Name two important antibiotic resistant bacteria.
- NEED TO KNOW:
- Beta-lactamase producing bacteria = resistant to penicillin-derived Ab
- MRSA = carries a gene called called mecA, which is a unique transpeptidase that is not inhibited by beta-lactam antibiotics. Hence, MRSA is able to continue peptidoglycan crosslinking and resist
116
Give 2 important examples of antibiotic resistance in Gram positive bacteria.
- MRSA = Methicillin resistant Staphylococcus aureus:
- Bacteriophage mediated acquisition of Staphylococcal cassette chromosome mec (SCCmec), contains resistance gene mecA
- Encodes penicillin-binding protein 2a (PBP2a)
- Confers resistance to all β-lactam antibiotics in addition to methicillin (= flucloxacillin)
- VRE = vancomycin-resistant enterococci
- Plasmid mediated acquisition of gene encoding altered amino acid on peptide chain preventing vancomycin binding
- Promoted by cephalosporin use
117
Give an important example of antiobiotic resistance in Gram negative bacteria.
- ESBL
- Further mutation at active site extended range of antimicrobial resistance to form extended spectrum beta lactamase (ESBL) inhibition
– These hydrolise oxyimino side chains of cephalosporins: cefotaxime, ceftriaxone, and ceftazidime and monobactams: aztreonam
118
Amoxicillin can be given to people infected with which bacteria?
H.influenzae, enterococci, e.coli, shigella, streptococci etc.
119
What are glycopeptides used in?
Penicillin allergy
120
What are macrolides used in?
Penicillin allergy and severe pneumonia
121
What is clindamycin used in?
Cellulitis (if allergic to penicillin) and necrosing fasciitis
122
What is doxyclycline used to treat?
Cellulitis (if they have a penicillin allergy) and pneumonia
123
What is gentamycin used to treat?
UTIs and infective endocarditis
124
What is Trimethoprim used to treat?
UTIs
125
Which organism are 85-90% of UTIs caused by?
- 85-90% of UTIs are caused by E.coli
- S.saprophyticus is also common in young women
126
What do we always treat UTIs with? How about in pregnancy? How does the treatment time differ between complicated and uncomplicated UTI?
- KNOW:
- ORAL NITROFURANTOIN or TRIMETHOPRIM
- Pregnancy: CEFALEXIN
- Simple = 3 days, complicated = 7 days
127
What antibiotic would you give to someone infected with staph. aureus (MSSA)?
Flucloxacillin
128
Which antibiotics are used for:
a) MRSA
b) Entamoeba histolytica, giardia
c) PCP
d) Pneumonia
e) C. difficile
- Vancomycin for MRSA
- Metronidazole for entamoeba histolytica, giardia
- Co-trimoxazole for PCP
- CURB65 score for pneumonia and their respective antibiotic regimens
- Vancomycin/Metronidazole for C. difficile
129
What are some side effects of aminoglycosides, e.g. Gentamicin?
- Ototoxicity
- Renal impairment
130
What are some side effects of Carbapenems?
Injection site reactions, diarrhoea, nausea, vomiting, skin rash and pruritus.
131
What are some side effects of Ciprofloxacin?
Nausea, vomiting, stomach pain, heartburn, diarrhoea
132
What are some side effects of Co-amoxiclav?
Diarrhoea, thrush and feeling or being sick
133
What are some side effects of Cephalosporins?
Stomach upset, nausea, vomiting, diarrhoea, yeast infection or oral thrush, dizziness
134
What are some side effects of Clindamycin?
Nausea, vomiting, unpleasant or metallic taste in the mouth, joint pain, pain when swallowing, heartburn, white patches in the mouth, thick, white vaginal discharge
135
Which drugs are most commonly used to treat TB?
RIPES:
- Rifampicin
- Isoniazid
- Pyrazinamide
- Ethambutol
- Streptomycin
136
What are the side effects of the drugs used to treat TB?
Remember RIPES:
- R = rifampicin = red-orange secretions and urine
- I = isoniazid = peripheral neuritis
- P = pyrazinamide = increase in uric acid
- E = ethambutol = visual problems
- S = streptomycin = ototoxic
137
What are the features of fungi? How do they move?
- Fungi = eukaryotes and have a cell wall of chitins and glucans (polysaccharides)
- Move by growing across or through structures or by dispersion in air/water
138
Which 2 forms do fungi exist in?
- Yeast - single cell that divide via budding
- Moulds - form multicellular hyphae or spores
139
What are dimorphic fungi? Give an example.
Fungi that can exist as both yeast and mould; they are yeast in tissues but mould in vitro. Example of dimorphic fungi = Coccidioides immitis
140
Why are severe fungal infections rare?
Fungi are unable to grow at 37°C and are often killed by the innate and adaptive immune response
141
Which antifungals target cell walls/plasma membranes?
Azoles
142
What test can be done to identify fungal antigens?
β-D-Glucan test
143
What fungal infection can often be a presenting factor for HIV?
Pneumocystis pneumonia; opportunistic infection, can cause lung infection in immunocompromised people
144
What are moulds composed of? Give examples of mould.
Branched filamentous filaments called hyphae. Examples = Aspergillus fumigatus, Aspergillus niger
145
What are the two fungi to know?
- Candida albicans: most pathogenic Candida spp. Vaginal and oral infections, sepsis (candidiasis) + line/catheter infections. Can kill rapidly
- Aspergillus fumigatus: most pathogenic Asp. spp. Predominantly lung infections, allergic disease. Poor prognosis but kills slowly
146
How do we treat Candida albicans?
Treat with antifungals, e.g. topical nystatin, oral fluconazole
147
How do we treat Pneumocystis pneumonia?
Co-trimoxazole
148
Aspergillosis is very common and usually causes no harm. Which patients are likely to be infected with Aspergillosis?
Cystic fibrosis and bronchiecstasis patients
149
Give 4 disadvantages of azoles.
1. High first pass metabolism, bioavailability = 45%
2. ADR's, can cause hepatitis
3. Drug interactions due to CYP450
4. Resistance can develop e.g. in candida
150
Chains of purple cocci are seen on a gram film. They don't grow near the optochin disc. These are probably:
Streptococcus pneumoniae
Staphylococcus epidermidis
Viridans Streptococci
Group A streptococci (S. pyogenes)
Neisseria meningitidis
Streptococcus pneumoniae
151
A pink colony is picked off this MacConkey plate and is found to contain pink staining bacilli with Gram's staining. Which organism is most likely?
Shigella sonnei
Listeria monocytogenes
Neisseria meningitidis
Eschericia coli
Streptococcus pyogenes
Eschericia coli
152
Which of the following is Haemophilus influenzae NOT an important cause of?
Meningitis in pre-school children
Otitis media
Pharyngitis
Gastroenteritis
Exacerbations of Chronic Obstructive Pulmonary Disease (COPD)
Gastroenteritis
153
Which is a normally sterile site?
The pharynx
The urethra
Cerebrospinal fluid
The lung
Skin
Cerebrospinal fluid
154
Which of these is NOT a means by which viruses cause disease?
Direct destruction of host cells
Cell proliferation and cell immortalisation
Inducing immune system mediated damage
Endotoxin production
Modification of host cell structure or function
Endotoxin production
155
When diagnosing viral infections which is true?
The sample must come from a sterile site
Electron microscopy is most appropriate
A black charcoal swab maintains virus better
PCR results take a week or more
A detectable IgM in serum may be diagnostic
A detectable IgM in serum may be diagnostic. Whilst it can make it simpler to identify a true pathogen if it is isolated from a sterile site, this is not required and is also less of a concern for diagnosing viral infection. Electron microscopy is rarely used as it is expensive and time consuming. Charcoal swabs are designed for bacterial specimens, green swabs have special viral transport medium. PCR is rapid and can give results the same or next day. IgM is an acute antibody response and when detected against a virus in serum may often confirm the diagnosis of an acute infection.
156
Which is most accurate? The HIV virus envelope contains:
RNA + capsid + DNA polymerase
DNA + capsid + RNA reverse transcriptase
DNA + p24 + RNA polymerase
RNA + capsid + RNA reverse transcriptase
RNA + gp120 + RNA polymerase
RNA + capsid + RNA reverse transcriptase. HIV is an enveloped virus studded with glycoprotein gp120. In side the envelope is a protein capsid (p24) which contains single stranded viral RNA and viral enzymes including RNA reverse transcriptase and viral protease.
157
Which pair is correct?
Toxoplasma = bacteria
Ringworm = helminth
Aspergillus fumigatus = mycobacteria
Falciparum malariae = filarial worm
Giardia lamblia = protozoa
Giardia lamblia = protozoa. Giardia is a flagellated protozoa. So are toxoplasma and Falciparum malaria. Aspergillus is a fungus, ringworm is a real diagnosis but a misnomer - it is a skin fungal infection not a worm infection.
158
Mycobacteria vs Bacteria. Which are which
a) Resist destaining by acid and alcohol
b) Cell wall contains lipoarabinomannan
c) They divide every 30-60 minutes
d) They usually withstand phagolysosomal killing
e) May cause meningitis
Resist destaining by acid and alcohol
Cell wall contains lipoarabinomannan
They divide every 30-60 minutes
They usually withstand phagolysosomal killing
May cause
a) Mycobacteria
b) Mycobacteria
c) Bacteria
d) Mycobacteria
e) Bacteria
159
Regarding antimicrobial resistance, which are true?
a) It is spread by plasmid mediated gene transfer
b) Spontaneous gene mutations do not occur
c) MRSA refers to vancomycin resistant S. aureus
d) Meropenem is effective against all gram negative bacteria
e) Broad spectrum agents promote resistance in the gut microbiome
a) True
b) False
c) False
d) False
e) True
160
What are the symptoms of C.difficile? Describe the treatment.
- Symptoms: diarrhoea, fever, abdominal pain
- Treatment: ORAL FIDAXOMICIN OR VANCOMYCIN
161
Match with correct option:
a) use for MRSA
b) first line for S. pyogenes
c) a carbapenem
d) a macrolide
e) contains a Beta-lactamase inhibitor
i) Penicillin
ii) Meropenem
iii) Glycopeptides
iv) Co-amoxiclav
v) Clarithromycin
1/1
Penicillin
Meropenem
Glycopeptides
Co-amoxiclav
Clarithromycin
a) iii
b) i
c) ii
d) v
e) iv
162
A 21 year old complains of myalgia, sore throat and tiredness. He is febrile and has an enlarged spleen. Which is the best answer?
a) He has sepsis and needs broad spectrum antimicrobial therapy with cefotaxime
b) A charcoal throat swab will confirm the diagnosis
c) Tests show atypical lymphocytes and detectable EBV IgM in serum
d) PCR on a viral throat swab will confirm the diagnosis
e) This is a viral upper respiratory tract infection and doesn’t warrant investigation
c) Tests show atypical lymphocytes and detectable EBV IgM in serum
163
Infection control: which is false? The five steps of hand hygiene are to wash hands:
a) Before contact with patient
b) Before bodily fluid exposure
c) Before aseptic procedures
d) After contact with patient surroundings
e) After patient contact
a) True
b) False
c) True
d) True
e) True
164
What is UNAIDS 90/90/90?
- A global target of:
- 90% of people living with HIV being diagnosed
- 90% diagnosed on ART (antiretroviral therapy)
- 90% viral suppression for those on ART by 2020
165
What are 4 main problems that surround HIV treatment?
1. Mainly transmitted by sexual intercourse and so people don't like to talk about it - taboo
2. Period of latency means someone may infect others unwittingly
3. HIV leads to a weakened immune system and so there is increased risk of infection
4. HIV mutates a lot and so drug treatment is difficult
166
Name 5 groups of people who are at high risk of HIV infection.
1. Homosexual men.
2. Heterosexual women.
3. Sex workers.
4. IV drug users.
5. Truck drivers.
167
HIV: what is the 'window period'?
The time between potential exposure to HIV infection and the point when the test will give an accurate result. During this time a person can be infected with HIV and be very infectious but still test HIV negative.
168
If a HIV test comes back as negative in a high risk individual why should a second HIV test be done?
A second test should be done after the window period: the window period is the time between exposure to HIV infection and the point when the test will give an accurate result. During this time a person can be infected with HIV and be very infectious but still test HIV negative.
169
How can the impact of HIV be reduced?
1. Behaviour change: education, condom use, needle exchange
2. Knowing your status
3. Specific interventions e.g., PrEP (pre-exposure prophylaxis)
170
How can sexual transmission of HIV be reduced?
- Condom use
- Male circumcision
171
Briefly explain why voluntary medical male circumcision can reduce sexual transmission of HIV.
- Male circumcision leads to a change in mucosa. HIV is less able to penetrate due to an increase in keratinisation
- Inner part of the foreskin contains many Langerhans cells that are prime targets for HIV - some of these are removed with the foreskin
172
What are the 4 main phases in the natural history of HIV? Describe each stage.
1. Acute primary infection = transient fall in CD4+ count followed by a gradual rise. There is also an acute rise in viral load.
2. Asymptomatic phase = progressive loss of CD4+ cells. This is the latent phase and can last for years.
3. Early symptomatic HIV. A 'late' diagnosis of HIV would be when CD4+ count \< 350
4. AIDS = when CD4+ cell count \< 200
173
How can HIV amongst young children be eliminated?
Reduce mother to child transmission (MTCT), e.g. reduce breast feeding
174
What type of virus is HIV?
HIV is a lentivirus (long incubation period) that uses reverse transcriptase to replicate (retrovirus)
175
Where does HIV replicate within? What does the virus cause?
HIV replicates within CD4 cells and causes immunodeficiency
176
Why are mutations common in HIV?
HIV is a retrovirus and replicates via reverse transcription. This process is prone to errors and mutations.
177
What did HIV arise from?
HIV arose from SIV - originally from chimpanzees (HIV-1 from SIV cpz and HIV-2 SIV sm)
178
What is the effect of HIV infection on CD4 count?
HIV leads to uncontrolled CD4 activation and apoptosis. CD4 numbers decrease over time
179
Which glycoproteins are on the surface of HIV?
GP41 and GP120
180
Briefly describe the mechanism of HIV replication.
- Attachment: GP120 binds to CD4 receptors
- Cell entry: viral capsid, enzymes and nucleic acids are uncoated and released into the cell
- Interaction with host cells: use cell materials (enzymes, amino acids, nucleotides) for their replication; subvert host cell defence mechanisms
- Replication: production of nucleic acids and proteins. RNA is converted into DNA using reverse transcriptase, viral DNA is integrated into cellular DNA by intergrase, viral DNA is transcribed into viral proteins
- New HIV cells 'bud' from CD4 either by lysis or exocytosis
181
Name 4 enzymes involved in HIV replication.
1. Reverse transcriptase.
2. Integrase.
3. RNA polymerase.
4. Proteases.
182
How many genes are encoded in the HIV genome?
9
183
Name 4 'sanctuary sites' for HIV.
1. Genital tract.
2. GI tract.
3. CNS.
4. Bone marrow.
184
Name 2 markers that are used to monitor HIV infection.
- CD4 cell count
- HIV RNA copies (viral load)
185
Which antigen can be tested for when testing for HIV?
p24 antigen
186
What is the normal range of a CD4 cell count? At what CD4 count is the patient considered to have end-stage HIV (AIDS)?
- Normal CD4 cell count: 500-1200 cells/m^3
- End-stage HIV (AIDS): \<200 cells/mm^3
187
What is viral load (HIV)? What is classed as an 'undetectable' viral load? What can the viral load count look like in untreated HIV?
Viral load is the number of copies of HIV RNA per ml of blood. “Undetectable” refers to a viral load below the lab’s recordable range (usually 50 – 100 copies/ml). The viral load can be in the hundreds of thousands in untreated HIV.
188
What is HIV seroconversion?
A period of time during which HIV antibodies develop and become detectable. Seroconversion generally takes place within a few weeks of initial infection.
189
Which symptoms are common during acute HIV infection (seroconversion)?
Fever, sore throat, myalgia, rash
190
What are some AIDS-defining illnesses?
- Kaposi’s sarcoma
- Pneumocystis pneumonia (PCP) - this is the most common opportunistic infection
- Cytomegalovirus infection
- Candidiasis (oesophageal or bronchial)
- Lymphomas
- Mycobacterium tuberculosis (TB)
191
How is AIDS diagnosed?
- CD4 count \< 200
OR
- An AIDS-defining illness
192
What are the characteristic signs of pneumocystis pneumonia (PCP)?
- Decreased CD4+ count.
- Decreased O2 sats on exertion.
- Decreased exercise tolerance
193
Name 3 CNS diseases associated with HIV.
1. Mass lesions, e.g. primary CNS lymphoma, cerebral toxoplasmosis
2. Meningitis, e.g. pneumococcal, cryptococcal
3. Opthalmic lesions, e.g. CMV, toxoplasmosis, choroidal tuberculosis etc.
194
What does HAART stand for?
Highly active anti-retroviral treatment
195
What is HAART? What does it aim to do? Name a couple of different classes of HAART drugs.
- Anti-retroviral treatment where 3 drugs are taken together.
The aim is to reduce viral load and increase CD4+ count. Good compliance = good prognosis
- There are a number of classes of HAART medications that work slightly differently on the virus, e.g. protease inhibitors (PIs), integrase inhibitors (IIs)
196
What colour do gram positive bacteria stain?
* Red
* Blue
* Pink
* Purple
Purple
197
Which of these tests differentiate the types of Streptococci?
* Haemolysis
* Catalase
* Coagulase
* Oxidase
Haemolysis
198
True or false: Staph aureus gives a positive result with the coagulase test
True
199
Which of the following describes Shigella?
* Gram positive bacilli, non-lactose fermenting
* Gram negative bacilli, lactose fermenting
* Gram negative cocci, positive oxidase test
* Non-lactose fermenting, negative oxidase test
Non-lactose fermenting, negative oxidase test
200
Which of these is an example of Group A streptococci?
* S.pneumoniae
* S.pyogenes
* S.viridans
* S.agalactiae
S.pyogenes
201
Which class of antibiotic does not inhibit cell wall synthesis?
* Glycopeptides
* Macrolides
* Cephalosporins
* Penicillins
Macrolides
202
Which antibiotic should you use to treat MRSA?
* Vancomycin
* Clarithromycin
* Benzylpenicillin
* Cephalexin
Vancomycin
203
Which stain is used for mycobacteria?
* Lowenstein-Jensen
* Oxidase purple
* Methylene blue
* Ziehl-Neelsen
Ziehl-Neelsen
204
Which of these is the most appropriate way of detecting viruses?
* Light microscopy
* Culturing
* PCR
* API Strip
PCR
205
What is the role of catalase test?
A: identifies staph aureus
B: identifies staph from non-staph
C: identifies mycobacterium
D: identifies fungi
B. identifies staph from non-staph
206
What is the role of coagulase test?
A: identifies staph aureus
B: identifies staph from non-staph
C: identifies mycobacterium
D: identifies fungi
A. identifies staph aureus
207
For which group of bacteria should you do an optochin test?
A: alpha-haemolytic staph
B: alpha-haemolytic strep
C: beta-haemolytic strep
D: enterococcus
B. alpha-haemolytic strep
208
Optochin +ve test: what is the bug?
A: strep pneumoniae
B: strep viridians
C: strep pyogenes
D: strep agalactiae
A. strep pneumoniae
209
Example of group A strep?
A: strep pneumoniae
B: strep viridians
C: strep pyogenes
D: strep agalactiae
C. strep pyogenes
210
Example of group B strep?
A: strep pneumoniae
B: strep viridians
C: strep pyogenes
D: strep agalactiae
D. strep agalactiae
211
Which of the following describes C. difficile?
A: gram –ve bacilli
B: gram –ve cocci
C: gram +ve cocci
D: gram +ve bacilli
D. gram +ve bacilli
212
Antibiotic for C. difficile
A: amoxicillin
B: cefotaxime
C: carbapenem
D: metronidazole
D. metronidazole
213
Which of the following is gram +ve diplococci on microscopy?
A: Neisseria gonorrhoea
B: strep pneumoniae
C: Moraxella catarrhalis
D: mycobacterium tb
B. strep pneumoniae
214
Which of the following is gram -ve diplococci on microscopy
A: Neisseria gonorrhoea
B: strep pneumoniae
C: Moraxella catarrhalis
D: mycobacterium tb
A. Neisseria gonorrhoea
215
When is chocolate agar important?
To culture:
A: mycobacterium tb
B: haemophilus influenza
C: Treponema pallidum
D: Not important, blood agar can be substituted
B. haemophilus influenzae
216
MacConkey test – shows yellow, what possible bug?
A: pseudomonas aeruginosa
B: e.coli
C: klebsiella pneumoniae
A. pseudomonas aeruginosa
217
MacConkey test – shows pink, what bug?
A: pseudomonas aeruginosa
B: staph aureus
C: strep pneumoniae
D: e.coli
D. e.coli
218
Which stain is needed for mycobacteria?
A: Lowenstein-Jensen stain
B: Methylene blue
C: Oxidase purple
D: Ziehl-Neelsen stain
D. Ziehl-Neelsen stain
219
What is cefuroxime? How does it work?
- Cefuroxime is a second-generation cephalosporin
- Cephalosporins are antibacterials that attach to penicillin binding proteins to interrupt cell wall biosynthesis, leading to bacterial cell lysis and death
220
What are the side effects, indications, contraindications and interactions of cefuroxime?
- Side effects: increased risk of infection. For cephalosporins: abdominal pain, diarrhoea, dizziness, eosinophilia, headache etc.
- Indications: susceptible infections due to Gram-positive and Gram-negative bacteria, hospital-acquired pneumonia, cellulitis
- Contraindications: those with cephalosporin hypersensitivity
- Interactions: N/A unless specified
221
What is chloramphenicol?
Chloramphenicol is a potent broad-spectrum antibiotic. It is used to treat a number of bacterial infections. This includes use as an eye ointment to treat conjunctivitis
222
What are the side effects, indications, contraindications and interactions of chloramphenicol?
- Side effects: aplastic anaemia (rare and with parenteral use)
- Indications: superficial eye infections, bacterial infection in otitis externa, life threatening conditions particularly those caused by Haemophilus influenzae
- Contra-indications: with intravenous use or oral use - acute porphyrias
- Interactions: warfarin, phenytoin, rifampicin
223
What is co-amoxiclav?
- It is a combination consisting of amoxicillin, a β-lactam antibiotic, and potassium clavulanate, a β-lactamase inhibitor
- The penicillins are bactericidal and act by interfering with bacterial cell wall synthesis
224
What are the side effects, indications, contra-indications and interactions of co-amoxiclav?
- Side effects: increased risk of infection (common) dizziness, dyspepsia, headache (uncommon). For penicillins: diarrhoea, hypersensitivity, nausea, skin reactions, thrombocytopenia, vomiting
- Indications: infections due to beta-lactamase-producing strains (where amoxicillin alone not appropriate), acute diverticulitis, moderate-severe diabetic foot infection, leg ulcer infection, cellulitis
- Contra-indications: acute and chronic lymphocytic leukaemia, cytomegalovirus infection, glandular fever
- Interactions: amoxicillin is in co-amoxiclav - warfarin, methotrexate, allopurinol, phenindione
225
What is erythromycin? How does it work?
- Erythromycin is an antibiotic used for the treatment of a number of bacterial infections. It is a macrolide
- Erythromycin acts by inhibition of protein synthesis
226
What are the side effects, indications, contra-indications and interactions of erythromycin?
- Side effects: hearing loss (rare,can occur after large doses). Macrolides: angioedema, anxiety, arrhythmias, candida infection; chest pain, constipation, drowsiness
- Indications: susceptible infections in patients with penicillin hypersensitivity, impetigo, cellulitis
- Contra-indications: avoid in acute porphyrias
- Interactions: warfarin, tamsulosin, simvastatin, prednisolone
227
What is rifampicin? How does it work?
- Rifampicin is an antibiotic used to treat several types of bacterial infections
- Rifampicin inhibits bacterial DNA-dependent RNA synthesis by inhibiting bacterial DNA-dependent RNA polymerase
228
What are the side effects, indications, contra-indications and interactions of rifampicin?
- Side effects: nausea, thrombocytopenia, vomiting. Uncommon: diarrhoea, leucopenia
- Indications: brucellosis in combination with other antibacterials, Legionnaires disease in combination with other antibacterials, serious staphylococcal infections in combination with other antibacterials, endocarditis in combination with other drugs, TB in combination with other drugs, leprosy
- Contra-indications: acute porphyrias, jaundice
- Interactions: amlodipine, bisoprolol
229
What would be the standard antibiotic treatment for endocarditis caused by strep. viridans and for how long? Why?
- IV benzylpenicillin for 4-6 weeks +/- synergystic gentamicin for the first 2 weeks
- Benzylpenicillin is an IV formulation of penicillin that damages the peptidoglycan cell wall of the Streptococci. This makes the bacteria susceptible to gentamicin (which targets the ribosome to inhibit protein synthesis) and the two antibiotics work synergistically to have a bactericidal effect
230
What is the standard antibiotic management of endocarditis caused by enterococcus?
IV amoxicillin and gentamicin for 4-6 weeks. Enterococci are usually sensitive to amoxicillin - which the lab can confirm by calculating the MIC (minimum inhibitory concentration) of amoxicillin that is needed to stop the growth of the isolate. It will become susceptible to gentamicin once the amoxicillin has damaged and permeabilised the peptidoglycan cell wall and so the two antibiotics can be used synergistically
231
c) Streptococcus pyogenes
232
e) Ziehl-Neelson stain
233
a) Rifampicin
234
True
235
b) Macrolides
236
237
d) Hepatitis B surface antigen
238
b) Streptococcus pneumoniae
239
a) Get bloods before antibiotics
240
b) a bacterial meningitis
241
a) Purple
242
c) PCR. Rapid, accurate, fairly cheap nowadays
243
a) CD4+
