1
Q
Define asymptomatic carriage
A
When a pathogen is carried harmlessly at a tissue site where it causes no disease
2
Q
What is unusual about chlamydia compared to other bacteria?
A
It can only grow inside a host cell
3
Q
Put the following in average size order:
bacteria, protozoa, virus
A
from largest to smallest:
Protozoa
Bacteria
Virus
4
Q
When do bacteria produce spores?
A
When they run out of nutrients
A spore will only germinate once conditions are suitable again
5
Q
Define heat labile
A
Can be unfolded through heating
6
Q
What is special about obligate intracellular bacteria
A
They may not be cultured on artifical media
7
Q
What is a molliculite?
A
Bacteria that we can grow on artifical media WITHOUT cell walls
8
Q
5 stages of viral replication
A
- Attachment to a specific receptor
- Cell entry - uncoating of virion within cell
- Host cell interaction + replication - transcription & translation
- Assembly of virion
- Release of new virus particles
9
Q
Define protazoa
A
A single celled eukaryotes (have a nucleus)
10
Q
Name of the adult form a protazoa
A
Trophozoite
11
Q
5 major groups of trophozoites
A
Flagellate
Amoebae
Microsporidia
Sporozoa
Ciliates
12
Q
Biological role of protazoa
A
Consumers of bacteria, algae, microfungi
13
Q
4 spcies of malaria that cause disease?
A
Plasmodia falciparum
Plasmodia ovale
Plasmodia vivax
Plasmodia malariae
14
Q
Give the 8 stages of the lifecycle of malaria
A
- Mosquito bites somebody with malaria → ingests gametocytes
- Gametocytes mature in the mosquitos gut, invade blood stream & move to salivary glands
- Mosquito bites somebody else & transfers sporozoites to this person
- Sporozoites infect hepatocytes
- Develops into a schizont which bursts & infects RBCs
- Within the RBC, plasmodium becomes a trophozoite
- The trophozoite develops into a schizont which ruptures and re-infects another RBC
- Some trophozoites develop into gametocytes which are taken up by mosquitos
- Process repeats
15
Q
Malaria treatment
A
Complicated/severe malaria = IV artesunate
Mild = lots of options, treat what is failing
16
Q
3 key attributes of a pathogen to cause disease
A
Infectivity
Virulence
Invasiveness
17
Q
How do beta-lactams work?
A
- Disrupt peptidoglycan production
- By covalently binding to penicillin binding proteins (PBPs)
- Cell wall is disrupted & lysis occurs
- Hypo-osmotic & iso-osmotic environment
- Active only against rapidly multiplying organisms
18
Q
4 subclasses of beta-lactams
A
Penicillins
Cephalosporins
Carbapenems
Monobactams
19
Q
Do beta-lactams work better in destroying gram negative or gram positive bacteria?
A
Gram positive
20
Q
4 majors types of antibiotic
A
Beta lactams
Inhibiting nucleic acid synthesis
Inhibiting protein synthesis
Inhibiting folate synthesis
21
Q
What are we trying to achieve when giving antibiotics?
A
Giving the immune system time and support to deal with an infection
22
Q
2 main strains of HIV that affect humans
A
HIV-1
HIV-2 (mainly confined to West Africa)
23
Q
How many genes does HIV express?
A
10
24
Q
What is the main characteristic of a lentivirus?
A
Characterised by long incubation periods
25
Barriers to HIV-1 vaccine development?
Live attenuated or killed vaccines are deemed too risky for HIV
HIV-1 is highly variable
A succesful vaccine would need to provide protection against HIV acquisiton by different routes
26
What does TasP stand for?
Treatment as prevention (usually refers to HIV)
27
What does PreP refer to in terms of HIV
Pre-exposure prophylaxis
28
What does U=U stand for in terms of HIV?
Undetectable = Untransmittable
29
What enzyme does HIV use to replicate?
Reverse transcriptase
30
What cell type does HIV replicate within?
CD4 cells
31
2 markers used to monitor HIV infection?
CD4 cell count
HIV viral load
32
From point of infection with HIV, roughly how long does it take to develop symptoms?
2-4 weeks
33
5 stages of HIV infection?
1. Primary infection
2. Acute HIV syndrome
3. Clinical latency
4. Opportunistic disease
5. Death
34
Describe clinical latency
In undiagnosed HIV:
1. Immune system produces CD4 cells & pop. increases
2. Viral load temporarily decreases
3. However, CD4 pop. will begin to slowly decline → immunosuppression
4. Until pt presents with constitutional symptoms & opportunistic infections
35
Most common AIDS defining illness
Pneumocystis Pneumonia
36
What does HAART stand for?
Highly active anti-retroviral therapy
37
How does HAART work?
Usually 3+ antiretroviral drugs
Act on different points in replication cycle to suppress viral replication
38
4 classes of drugs used in HAART?
Reverse transcriptase inhibitors
Fusion/entry inhibitors
Intergrase inhibitors
Protease inhibitors
39
How does triple therapy have an advantage over monotherapy in terms of HIV drug resistance?
1 HIV mutation in every 2 new viruses produced
1-10 billion new virus particles each day
1-5 billion mutations per day
With monotherapy, the mutant has a higher survival advantage
40
2 ways HIV develops drug resistance?
Non-adherence
Drug-drug resistance
41
Give an example of drug-drug interaction that may lead to HIV drug resistance
If lansoprazole (proton pump inhibitor) is given to a patient who is on rilpivirine
Significant decreases in rilpivirine plasma concentrations occur due to gastric pH increase
Loss of therapeutic effect of rilpivirine → resistance
42
Chains of purple cocci are seen on a gram film.
They appear as above when grown on blood agar.
They don't grow near the optochin disc (not shown). These are probably:
* - Streptococcus pneumoniae
* - Staphylococcus epidermidis
* - Viridans Streptococci
* - Group A streptococci (S. pyogenes)
* - Neisseria meningitidis
Streptococcus pneumonia
43
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
(Yes. E coli is a lactose fermenting gram negative bacillus. Listeria (bacilli), and Steptococci (cocci) are gram positive (purple). Neisseria are gram negative cocci not bacilli. Shigella species are non lactose fermenting - colourless / pale white on MacConkey)
44
Which of the following is Haemophilus influenzae NOT an important cause of?
* Meningitis in pre-school children
* Otitis media
* Pharyngitis
* Gastroenteritis
* Exacerbations of COPD
Gastroenteritis
H influenzae is a gram negative 'cocco-bacillus' - a short pink rod responsible for many types of respiratory tract infection. It does not cause gastroenteritis.
45
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
46
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
47
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
48
Which pair is correct?
* Toxoplasma = bacteria
* Ringworm = helminth
* Aspergillus fumigatus = mycobacteria
* Falciparum malariae = filarial worm
* Giardia lamblia = protozoa
Giardia lamblia = protozoa
| (ringworm = misnomer, fungal infection)
49
Mycobacteria vs Bacteria. Which are which?
* Resist destaining by acid and alcohol
* Cell wall contains lipoarabinomannan
* They divide every 30-60 minutes
* They usually withstand phagolysosomal killing
* May cause meningitis
Mycobacteria
* Resist destaining by acid and alcohol
* Cell wall contains lipoarabinomannan
* They usually withstand phagolysosomal killing
Bacteria:
* They divide every 30-60 minutes
* May cause meningitis
50
Regarding antimicrobial resistance, is the following true or false?
It is spread by plasmid mediated gene transfer
True
51
Regarding antimicrobial resistance, is the following true or false?
Spontaneous gene mutations do not occur
False
52
Regarding antimicrobial resistance, is the following true or false?
MRSA refers to vancomycin resistant S. aureus
False
53
Regarding antimicrobial resistance, is the following true or false?
Meropenem is effective against all gram negative bacteria
False
54
Regarding antimicrobial resistance, is the following true or false?
Broad spectrum agents promote resistance in the gut microbiome
True
55
56
A 34 year old gay man who has had prolonged diarrhoea now presents short of breath with a dry cough and hypoxia. His chest x-ray is shown. Which is most accurate?
* This is bacterial pneumonia caused by pneumocystis jirovecii.
* It is too early for a 4th generation HIV test to be positive
* The CD4 T cell count will be between 500 and 750
* Even if the HIV test is negative this man has AIDS
* With appropriate therapy he has a good prognosis
With appropriate therapy he has a good prognosis
57
Infection control: which is false? The five steps of hand hygiene are to wash hands
* Before contact with patient
* Before bodily fluid exposure
* Before aseptic procedures
* After contact with patient surroundings
* After patient contact
* Before contact with patient - true
* Before bodily fluid exposure - false
* Before aseptic procedures - true
* After contact with patient surroundings - true
* After patient contact - true
58
A 21 year old complains of myalgia, sore throat and tiredness. He is febrile and has an enlarged spleen. Which is the best answer?
* He has sepsis and needs broad spectrum antimicrobial therapy with cefotaxime
* A charcoal throat swab will confirm the diagnosis
* Tests show atypical lymphocytes and detectable EBV IgM in serum
* PCR on a viral throat swab will confirm the diagnosis
* This is a viral upper respiratory tract infection and doesn’t warrant investigation
Tests show atypical lympocytes and detectable EBV IgM in serum.
(This is consistent with acute infectious mononucleosis from EBV infection and typically leads to the development of atypical lymphocytes on a blood film and detectable IgM against EBV. None of the criteria for sepsis have been suggested in the clinical story. Although bacterial throat infections such as those from S pyogenes can be diagnosed with a charcoal swab, and acute viral respiratory infections can be diagnosed with PCR, neither cause enlarged spleens acutely. EBV can be detected with a viral PCR but it is often shed asymptomatically in the throat in people who have long since recovered, so not helpful for diagnosing an acute infection.)
