Microbiology

Question 1

What is meant by nosocomial infection and when can it be diagnosed?

Answer 1

An infection due to an organism which was acquired at hospital - can be diagnosed after 48 hours after admission to hospital

Question 2

Name 4 important bacterial causes of nosocomial infection and state whether they are gram positive or negative. (4+4)

Answer 2

Enterococcus Faecium – G+ve
Staphylococcus Aureus – G+ve
Clostridium Difficile – G+ve
Acinetobacter Baumanii – G-ve

Question 3

Some patient has a lung infection. List three ways to collect a sample from them

Answer 3

Bronchoalveolar lavage
Nasopharyngeal aspirtate
Lung biopsy
Sputum

Question 4

List four bacteria that can be cultured from them (sample lung infection)

Answer 4

Mycobacterium
Streptococcus pneumonia
Haemophilus influenza
Klebsiella pneumoniae

Question 5

Explain why looking at sputum and doing a tissue stain is useful

Answer 5

Sputum – easy to obtain and can test many diseases as the pathogens would be trapped in it
Tissue stain – Determines if gram negative or positive: so identifies appropriate treatment

Question 6

Give an example of a gram positive infection, say what antibiotic it is resistant to and say how the antibiotic works

Answer 6

Staphylococcus Aureus – resistant to methicillin

Methicillin – works by inhibiting activity of penicillin binding proteins that inhibit peptidoglycan synthesis

Question 7

Give examples of bacterial pathogens that can be vaccinated for

Answer 7

Haemophilus influenza
Neisseria Meningitides
Streptococcus pneumonia 
Clostridium diphtheria
Bordetella pertussis
Clostridium Tetani

Question 8

Give examples of bacteria causing respiratory tract infections

Answer 8

Legionella pneumophilia (Gram -ve)
Mycobacterium tuberculosis (mycobacterium)

Question 9

Give examples of bacteria causing STIs

Answer 9

Chlamydia trachomatis (obligate intracellular)
Neisseria gonorrhoeae (Gram -ve)
Treponema pallidum (causes Syphilis)

Question 10

Give examples of viruses causing STIs

Answer 10

HepB virus
HepC virus
HIV/AIDS

Question 11

List some food- and waterborne diseases and zoonoses

Answer 11

Campylobacterosis (?)
Cholera (Vibrio cholera)
Listeriosis (Listeria monocytogenes)
Shigellosis (Shigella spp.)

Question 12

Define an outbreak

Answer 12

When a greater number of individuals than what is normal or expected become infected or diagnosed with a particular infection in a given period of time or particular place or both

Question 13

How are outbreaks measured, and why is it important?

Answer 13

Identified by surveillance with an established and timely reporting system
Important to identify early, quarantine to prevent further transmission, identify organism and treat

Question 14

Name 4 types of protozoa and examples of each (4)

Answer 14

Amoeba – Entamoeba histolytic
Coccidia – Toxoplasma; Plasmodium spp.
Ciliates – Balantidium Coli
Flagellates - Trichromonas

Question 15

What is the difference between protozoa and metazoan?

Answer 15

Protozoa are single celled organisms which do not cause eosinophilia while metazoa are multi-celled organisms which do cause eosinophilia

Question 16

What are the two types of leishmaniasis and give features of each

Answer 16

Promastigote – in sand-fly vector. Can move in direction of their flagellum and can be cultured
Amastigote – In humans and other vertebrate hosts. No longer motile. Intracellular form of the parasite

Question 17

What cell type do leishmania reside in?

Answer 17

Macrophage

Question 18

What are endotoxins and exotoxins

Answer 18

Exotoxins – Toxins that are produced by bacteria and released extracellularly, e.g. neurotoxins and enterotoxins
Endotoxins – Lipid A moiety of lipoproteins produced by Gram negative bacteria which are shed in steady amounts from living bacteria

Question 19

What are Pyrogenic toxins

Answer 19

Exotoxins which stimulate cytokine release and thus cause fever

Question 20

Name the general term for the type of toxin that binds directly to both MHCII and T cell receptors.

Answer 20

Superantigens

Question 21

Name some virulence factors other than toxins that are used by bacteria

Answer 21

Diverse secretion system – e.g. camplylobacter
Flagella – e.g. camplylobacter
Pilli – e.g Neisseria 
Capsule- e.g. streptococcus pneumonia 
Endospores – e.g. clostridium species
Biofilms – e.g. pseudomonas aeruginosa

Question 22

Name two examples of flagellates and the diseases they cause

Answer 22

Giardia Lamblia – Diarrhoea, greasy stools, stomach or abdominal cramps, nausea and vomiting and dehydration
Trichromonas – discharge and dysuria

Question 23

Name two examples of coccidiae and the diseases they cause

Answer 23

Toxoplasma gondii – can cause toxoplasmosis

Cryptosporidium – diarrhoea, fever, nausea and vomitting

Question 24

Name the 3 helminth infections

Answer 24

Ascariasis (Ascaris roundworms)
Schistosomiasis (flukes - Schistosoma)
Taenia = Flatworms => taeniasis

Question 25

Two types of viruses with genetic drift and we have vaccines for them.

Answer 25

Influenza is one with genetic drift and vaccines available

Question 26

Explain Genetic drift vs Genetic shift.

Answer 26

Antigenic drift = Continued rapid evolution driven by antigenic pressure from the host
Antigenic shift = Introduction of a new subtype from an animal source therefore existing as a different genetically stable serotype that co-circulates in humans

Question 27

Talk about how viruses evade interferon detection

Answer 27

Hide PAMPS
Interfere globally with host cell gene expression and/or protein synthesis
Block interferon signalling cascade by destroying or binding to cascade components
Inhibit interferon signalling
Block activation of individual interferon induced antiviral enzymes
Activate SOCS suppression of interferon 1 induction
Have a replication strategy which is insensitive to interferon signalling

Question 28

Give two examples of cytoplasmic sensors for viruses

Answer 28

cGAS senses viral DNA in cell - binds to DNA - forms cGAMP - binds to STING on endoplasmic reticulum -> transcription factor phosphorylation and movement to nucleus e.g. IRF 3 -> interferon transcription

RIG also intracellular detector - RIG-I binds to viral ssRNA or mRNA => RIG-I binds to MAVS => IR3 or IR7 is phosphorylation and translocated into nucleus => transcription of interferon beta

Question 29

How does toll-like receptor (TLR) recognise viruses

Answer 29

Same way as RIG except it is membrane associated so only recognises endosomes or viruses outside of cell (RIG is intracellular sensor for viruses)
- detect viral RNA => IR3 or IR7 is phosphorylated => interferon transcription

Question 30

Name two bacterial pathogens that use pyrotoxins

Answer 30

Staphylococcus aureus

Streptococcus pyogenes