Microbiology

Question 1

What are commensals?

Answer 1

Presence, growth and multiplication of a microorganism on/in a host but without interaction between host and organism. Rarely cause disease, even in vulnerable individuals
• Staphylococcus epidermidis on the skin
• Lactobacillus in the gut
• Streptococcus salvarius oral microbiome

Question 2

What are opportunistic pathogens?

Answer 2

Caused by microorganisms that are commonly found in the host’s environment or flora without causing harm, however infection may arise in individuals with compromised immunity. Exploit opportunities, causing infections when defenses are compromised
• S. aureus can cause infection if enters the bloodstream
• Candida albicans can cause thrush (common in antibiotics use)
• P. aeruginosa can cause serious infection (immunocompromised, CF)

Question 3

Acute, subacute and chronic time periods

Answer 3

• acute(<4 weeks with rapid onset)influenza
• subacute(4-12 weeks, slower onset)endocarditis
• chronic(>12 weeks, long duration)tuberculosis

Question 4

Transmission can occur by…

Answer 4

• direct or indirect contact
• respiratory route
• food or waterborne transmission
• fecal-oral route
• sexual
• vector

Question 5

Evolved mechanisms for pathogens to damage host

Answer 5

Adhesion
Invasion
Colonisation
Immune evasion

Question 6

Chain of reaction

Answer 6

Question 7

How to break the chain of reaction

Answer 7

• Cleaning your hands frequently
• Staying up to date on your vaccines (including the flu)
• Covering coughs and sneezes and staying home when sick
• Following the rules for standard and contact isolation
• Using personal protective equipment correctly
• Cleaning and disinfecting the environment
• Sterilizing medical instruments and equipment
• Following safe injection practices
• Using antibiotics wisely to prevent antibiotic resistance

Question 8

Stages of infection

Answer 8

• Incubation- Time interval betweeninitial contactwith an infectious agent and appearance of thefirst sign or symptomof disease
• Infectious period (communicability)- Timewhen aninfectious agent may be transferred directly or indirectlyperson to another person, animal to human, or infected person to animal (host is infectious to others)
• Latent Period- Periodbetween exposureand theonset of the infectious period, which may be shorter or longer than incubation period

Question 9

Symbiotic relationship types

Answer 9

Question 10

Colonisation vs infection

Answer 10

Colonisation
- Many opportunistic bacteria are part of the normal human flora
- Exist on skin or mucosa without causing harm
- May provide benefit to host
- Biofilm formation on plastics

Infection
- Invasion of the body by pathogens causing disease

Question 11

What are the risk factors for a HCAI?

Answer 11

Health-care associated factors-

• Prolonged hospital admission
• Haemodialysis
• Immunosuppression
• Antibiotics within last 90 days
• Intensive care stay
• Prosthetic devices e.g. lines, catheter, ventilator

Patient factors-

• Extremes of age
• Immobility
• Chronic illness e.g. diabetes, COPD, obesity
• Pre-existing colonisation with bacteria e.g. MRSA, C. difficile

Question 12

What are the common causative pathogens of HCAIs?

Answer 12

Question 13

What are the routes of entry and source of pathogens?

Answer 13

Routes of entry-

Respiratory and urinary routes
- Main routes of entry for Gram negative bacteria
- Catheter associated UTI, hospital acquired pneumonia

Skin and soft tissue infections
- Gram positive bacteria
- Cannulas, pressure sores, surgical site infection

Source of pathogens-

Endogenous
- From patient’s own micro-flora
- Commonest

Exogenous
- Contaminated environment
- Cross-transmission from staff or other patients

Routes of infection
- Contact- hands, equipment, environment
- Air-borne
- Rarely- blood-borne

Question 14

What are UTIs and LRTIs?

Answer 14

Question 15

Where does sampling of pathogens take place?

Answer 15

Question 16

What infections is reporting mandatory for?

Answer 16

• MSSA and MRSA blood stream infections
• C. difficile
• E.coli, Klebsiella and Pseudomonas blood stream infections

Question 17

Communicable vs non-communicable diseases

Answer 17

Question 18

How are communicable diseases managed?

Answer 18

Measures that are directed to the agent

• Sterilisation – complete removal of all forms of living/infectious agents
• Disinfection - a process that eliminates many or all pathogenic microorganisms, except bacterial spores, on inanimate objects
• Antiseptics – disinfectants for use on skin
• Sanitisation - the cleaning and disinfection of an area or an item using heat or chemicals to reduce the number of microorganisms to safe levels.
• Proper treatment of infected individuals

Measures that are directed towards breaking transmission

• Isolation
• Decontaminating of fomites
• Promote handwashing
• Modify ventilation and air pressure
• Control vector population
• Environment: sanitation of water, food, proper sewage handling

Measures that are directed towards the reservoir

• Cases: Case finding, reporting to the local health authority in order to apply the appropriate control measures for contact and the environment, isolation (strict isolation or discharge/body fluid isolation) for the whole period of communicability and treatment, surveillance for the longest incubation period.
• Carriers: Identification of carriers in the community, treatment and
  exclusion from work till the organism is eliminated especially if food handlers or working with children. Its cost effectiveness depends on the proportion of carrier in the community as well as the sensitivity of their occupation.
• Animal reservoir: Adequate animal husbandry, immunisation of animals (if vaccine is available), treatment of infected animals and killing if treatment is not feasible.

Measures that are directed towards protecting the portal of entry

• Using bed-nets
• Wearing masks and gowns to prevent entry of infected body secretions or droplets through skin or mucous membranes
• Covering skin and using insect repellents

Measures that are directed towards the host

• Health education
• Adequate personal hygiene
• Sound nutrition
• Immunisation
• Chemoprophylaxis

Question 19

How are outbreaks managed in hospitals vs in the community

Answer 19

Question 20

What leads to resistance?

Answer 20

• Increased use of antibiotics
• Prescriptions taken incorrectly
• Sold without medical supervision
• Prophylactic use before surgery
• Antibiotics used for viral infection
• Spread of resistant microbes in hospitals due to lack of hygiene
• Patients who do not complete course
• Antibiotics in animal feeds

Question 21

What are the targets of different antibiotics resistance mechanisms?

Answer 21

Question 22

How do cells acquire resistance?

Answer 22

Question 23

What are examples of b-lactams

Answer 23

Penicillins (end in –cillin)
Benzylpenicillin, Phenoxymethylpenicillin, Amoxicillin, Ampicillin, Piperacillin, Carbenicillin, Ticarcillin,
Oxacillin, Flucloxacillin

Carbapenems (all end in –penem) used parenterally (via IV) can penetrate the BBB
Imipenem, Meropenem, Ertapenem

Cephalosporins (all start with Cef- or Ceph-)
1st Gen: Cephalexin, Cefazolin
2nd Gen: Cefotetan, Cefuroxime, Cefprozil, Cefoxitin
3rd Gen: Ceftriaxone, Cefotaxime, Cefixime, Cefdinir, Ceftazadime
4th Gen: Cefepime, Cefpirome
5th Gen: Ceftaroline

Monobactams
Aztreonam is the only approved

Question 24

What is the mechanism of b-lactam resistance?

Answer 24

Question 25

What are examples of macrolides?

Answer 25

End in –thromycin - Erythromycin (original macrolide) - Clarithromycin - Azithromycin

Question 26

What is the mechanism of macrolide resistance?

Answer 26

Question 27

What are examples of fluoroquinolones?

Answer 27

End in -floxacin - Ciprofloxacin (2nd gen) - Levofloxacin (3rd gen) - Moxifloxacin (4th gen)

Question 28

What is the mechanism of fluoroquinolone resistance?

Answer 28

Question 29

What are examples of aminoglycosides?

Answer 29

End in -mycin -micin -cin - Gentamicin - Tobramycin - Amikacin - Kanamycin - Streptomycin (first aminoglycoside) - Almost always used with another antibiotic, to broaden the spectrum of coverage or act as an adjunct for therapy. Administered parenterally (via IV)

Question 30

What is the mechanism of aminoglycoside resistance?

Answer 30

Question 31

How can antimicrobial resistance be monitored and managed?

Answer 31

**Infection Prevention & Control** - Minimising the transmission of organisms with successful antimicrobial resistance - Avoidance of infection and exposure to resistant organisms is key - We expose our most vulnerable patients to our highest-risk practice (hospitals) **Antimicrobial Usage** - Antimicrobial exposure exerts a selective pressure to enable organisms with inherent or acquired resistance to proliferate - Any reduction in antimicrobial usage will reduce risk of resistance - The ‘easy win’ is inappropriate usage - reduce broad spectrum antibiotics - reduce treatment duration? - reduce antibiotics when no infection is present

Question 32

What is antimicrobial stewardship?

Answer 32

“Antibiotic stewardship refers to a set of coordinated strategies to improve the use of antimicrobial medications with the goal of enhancing patient health outcomes, reducing antimicrobial resistance, and decreasing unnecessary costs”