Microbiology

Question 1

What bacteria have short incubation times (1-6 hours)?

Answer 1

Bacillus cereus, staph aureus.

Question 2

What type of bacterium is bacillus cereus and describe how it gets into the body and what it does.

Answer 2

Gram positive bacillus.

Colonises starchy food and has heat resistant spores (consumed with reheated rice), causes profuse vomiting.

Question 3

What foods does staph aureus colonise?

Answer 3

Foods left at room temperature. Milk, meat, fish.

Question 4

What does GI staph aureus infection cause?

Answer 4

Vomiting and abdominal pain.

Question 5

How do these pathogens have such short incubation times?

Answer 5

They have pre-formed toxin.

Question 6

What was the original shigella described by Shiga?

Answer 6

Shigella dysenteriae.

Question 7

How does Shiga-toxin work?

Answer 7

Binds to receptors found on renal cells, RBCs and others. Inhibits protein synthesis causing cell death.

Question 8

What are the 2 names for E.coli that produce shiga-like toxin?

Answer 8

STEC (shiga-like toxin producing E.coli, more recent), VTEC (verotoxin producing E.coli).

Question 9

What does shiga-like toxin produced by E.coli do when it enters the bloodstream via damaged epithelium?

Answer 9

Causes the death of vascular epithelium. Endothelial cell lysis, platelet activation and aggregation, cytokine secretion, vascular constriction contributing to fibrin deposition, clot formation within capillaries.

Question 10

What does HUS stand for?

Answer 10

Haemolytic uraemic syndrome.

Question 11

What causes haemolytic uraemic syndrome?

Answer 11

Microangiopathy as toxin carried to kidneys, causing clinical syndrome of haematuria and renal failure.

Question 12

What feature of E.coli O175 gastroenteritis is uncommon in other gastroenteritis?

Answer 12

Bloody diarrhoea/blood PR.

Question 13

How can E.coli O175 spread?

Answer 13

Food (beef, raw milk/water, wide range), person to person, animal contact.

Question 14

What is the most virulent kind of shiga toxin?

Answer 14

Type 2.

Question 15

What are the symptoms of HUS?

Answer 15

Abdominal pain, fever, pallor, petechiae (haemorrhagic spots), oliguria (diminished urine output), bloody diarrhoea.

Question 16

What would you see in blood tests for HUS?

Answer 16

High white cells, low platelets, low HB, red cell fragments.

Question 17

What investigations would you ask for if you suspect HUS?

Answer 17

Stool culture samples (all patients with blood in faeces), U&E, FBC, fil, LFT, clotting, urine, lactate dehydrogenase.

Question 18

What people does HUS normally affect?

Answer 18

Under 16s.

Question 19

What are the 3 parts of HUS?

Answer 19

Acute renal failure, thrombocytopenia (low platelets), haemolytic anaemia.

Question 20

What are 4 other E.coli pathotypes?

Answer 20

Enterotoxigen (ETC), enteropathogenic (EPEC), enteroinvasive (EIEC), enteroaggregative (EAIC).

Question 21

What foods does campylobacter live on?

Answer 21

Poultry and raw milk.

Question 22

What antibiotic would you give for campylobacter infection and when?

Answer 22

Macrolide e.g. clarithromycin. If there are co-morbid factors but there is increasing resistance.

Question 23

What food (and species) does salmonella colonise?

Answer 23

Food: poultry, meat, raw egg. Reptiles.

Question 24

What are the risk factors for listeria monocytogenes infection becoming invasive?

Answer 24

Immunosuppressed (particularly T cell), age>50, pregnant.

Question 25

What is the main complication of invasive listeria monocytogenes infection?

Answer 25

Meningitis/bacteraemia.

Question 26

What foods does listeria monocytogenes colonise?

Answer 26

Unpasteurised milk products, deli counter.

Question 27

How do you diagnose the causative organism for viral gastroenteritis?

Answer 27

PCR.

Question 28

What are the 3 main normal flora in the large bowel?

Answer 28

Enterobacteriaeceae (coliforms), enterococci, anaerobic gm-ve bacilli (bacteroides). Also anaerobic gm-ve cocci.

Question 29

What test can be used to differentiate between enterobacteriaceae?

Answer 29

The lactose fermenting test.

Question 30

Give some examples of lactose fermenting enterobacteriaceae.

Answer 30

E.coli, citrobacter, klebsiella, enterobacter, serratia.

Question 31

Give some examples of non-lactose fermenting enterobacteriaceae.

Answer 31

Morganella, proteus, providencia, salmonella, shigella, yersinia.

Question 32

Describe the process of identifying enterobacteracaea.

Answer 32

Appropriate clinical sample -> select correct culture medium -> perform gram stain -> lab selects appopriate biochemical tests -> report results to clinician -> other tests.

Question 33

Describe some types of agar in the identification of enterobacteriaceae.

Answer 33

MacConkey agar, CLED agar (cysteine lactose electrolytes deficiency), chromogenic.

Question 34

Are enterobacteriaceae aerobes or anaerobes?

Answer 34

Faculative anaerobes.

Question 35

Give an example of an enterotoxin.

Answer 35

Shiga-toxin.

Question 36

What is the problem with MALDI-TOF?

Answer 36

It doesn’t tell you what caused the illness, just that it is there.

Question 37

What are some other molecular methods of identifying pathogens?

Answer 37

16s RNA, whole genome sequencing, pulsed field gel electrophoresis, multilocus sequence typing (MLST), multiple locus variable number tandem repeat analysis (MVLA), SNP assays.

Question 38

What is the normal flora of the mouth?

Answer 38

Strep viridans, neiserria, anaerobes, candida, staph.

Question 39

What are the 3 types of strict anaerobes in the GI tract (mostly in large intestine)?

Answer 39

Clostridium sp, bacteroides sp, anaerobic cocci.