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Flashcards in Microbiology (Laz's) Deck (463)
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1

What are the four processes that occur in septicaemia?

Capillary leak – albumin and other plasma proteins lead to hypovolaemia
Coagulopathy – leads to bleeding and thrombosis, endothelial injury results in platelet release reactions, the protein C pathway and plasma anticoagulants are affected
Metabolic derangement – particularly acidosis
Myocardial failure – and multi-organ failure

2

What is a typical MRI feature of TB meningitis?

Leptomeningeal enhancement

3

Name two types of amoeba that cause encephalitis.

Naegleria fowleri
Acanthamoeba species and Balamuthia mandrillaris

4

What is toxoplasmosis and how is it spread?

Obligate intracellular parasite
Spread via oral, transplacental or organ transplant route
From raw/undercooked meats (particularly in France) and contact with cat faeces

5

List some organisms that can cause brain abscesses.

Staphylococci
Streptococci
Gram-negative organisms (mainly in neonates)
TB
Actinomyces and Nocardia species

6

Describe the Gram-stain and microscopic appearance of:
a. S. pneumoniae
b. N. meningitidis
c. L. monocytogenes
d. TB
e. Cryptococcus

a. S. pneumoniae
Gram-positive alpha-haemolytic diplococci
b. N. meningitidis
Gram-negative non-haemolytic diplococci
c. L. monocytogenes
Gram-positive rods
d. TB
Stains positively with Ziehl-Neelsen (red and blue)
e. Cryptococcus
Stains positively with India ink (appears like an orbit – yeast in the middle with a capsule around the outside)

7

What is another key clinical feature of Cryptococcal meningitis?

High opening pressure

8

What is the generic therapy used in meningitis?

Ceftriaxone 2 g IV BD
If > 50 years or immunocompromised = amoxicillin 2 g IV 4 hourly
NOTE: this is because ceftriaxone does NOT cover Listeria

9

What is the generic therapy used in meningo-encephalitis?

Aciclovir 10 mg/kg IV TDS
Ceftriaxone 2 g IV BD
If > 50 years or immunocompromised = amoxicillin 2 g IV 4 hourly

10

Name the specific therapy for meningitis caused by:
a. S. pneumoniae
b. N. meningitidis
c. H. influenzae
d. Group B Streptococcus
e. Listeria
f. Gram-negative bacilli
g. Pseudomonas

a. S. pneumoniae
Pen G 18-24 mu/day
b. N. meningitidis
Ceftriaxone 4 g/day
c. H. influenzae
Cefotaxime 12 g/day
d. Group B Streptococcus
Pen G 18-24 mu/day
e. Listeria
Ampicillin 12 g/day
f. Gram-negative bacilli
Cefotaxime 12 g/day
g. Pseudomonas
Meropenem 6 g/day

11

What type of toxin is produced by Staphylococcus aureus?

Enterotoxin – this is an exotoxin that can act as a superantigen in the GI tract triggering the release of IL1 and IL2

12

What type of organism is Bacillus cereus?

Gram-positive rods that are spore-forming

13

Name three types of Clostridium infection and describe the diseases that they cause.

Clostridium botulinum – causes botulism
• From canned food
• Causes disease due to preformed toxin which blocks acetylcholine release at peripheral nerve synapses
- Causes descending paralysis
• Treated with antitoxin
Clostridium perfringens – food poisoning
• From reheated food
• Generates a superantigen that mainly affects the colon
• Causes watery diarrhoea and cramps that last 24 hours
Clostridium difficile – pseudomembranous colitis
• Hospital-acquired infection related to antibiotic use

14

Which antibiotics are most commonly implicated in C. difficile colitis?

Cephalosporins
Clindamycin
Ciprofloxacin

15

What type of organism is Listeria monocytogenes?

Gram-positive, rod-shaped, facultative anaerobe
Beta-haemolytic, aesculin-positive with tumbling motility

16

What type of organisms are Enterobacteriaceae?

Facultative anaerobes
Lactose fermenters
Oxidase-negative

17

What type of bacteria are Salmonella enteritidis?

Gram-negatives
Oxidase negative
Urease negative
Non-lactose fermenting
Produce hydrogen sulphide (form black colonies)
Grows on TSI agar, XLD agar and selenite F broth

18

Which antigens are found on Salmonellae?

Cell wall O (groups A-I)
Flagellar H
Capsular Vi (virulence, antiphagocytic)
NOTE: differences in these antigens help identify types of Salmonellae

19

Describe the presentation of Salmonella typhi.

Slow onset fever and constipation
May cause splenomegaly, rose spots, bradycardia, anaemia and leucopaenia
Blood cultures may be positive
Transmitted only by humans
Ingested by monocytes and multiplies in Peyer’s patches and spreads via the endoreticular system

20

How is Salmonella typhi treated?

Ceftriaxone

21

List some types of Shigella.

Shigella sonnei
Shigella dysenteriae
Shigella flexneri (MSM)

NOTE: avoid antibiotic treatment (use ciprofloxacin if necessary)

22

What are the microbiological features of Vibrio?

Comma-shaped
Late lactose-fermenters
Oxidase-positive
Gram-negative

23

Name and describe the key features of other types of Vibrio.

Vibrio parahaemolyticus – caused by ingestion of raw/undercooked seafood, causes self-limiting diarrhoea, grows on salty agar
Vibrio vulnificus – causes cellulitis in shellfish handlers, can cause fatal septicaemia with D&V in HIV patients, treated with doxycycline

24

What are the main microbiological features of Campylobacter?

Comma-shaped
Microaerophilic
Oxidase-positive
Gram-negative
Motile

25

What are the key microbiological features of Entamoeba histolytica?

Motile trophozoite in diarrhoeal illness
Non-motile cyst in non-diarrhoeal illness
Killed by boiling
Contains four nuclei
No animal reservoir

26

Describe the pathophysiology of diarrhoeal illness caused by Entamoeba histolytica?

Ingestion of cysts  trophozoites move into the ileum  colonise the colon  causes flask-shaped ulcers

27

How is Entamoeba histolytica infection diagnosed and treated?

Diagnosis: stool microscopy, serology of invasive disease
Treatment: metronidazole + paromomycin

28

What are the key microbiological features of Giardia lamblia?

Pear-shaped trophozoites
Two nuclei
Four flagellae and a suction disc

29

Outline the pathophysiologiy of GI disease caused by Giardia.

Transmitted by ingestion of cyst from faecally contaminated water
Excystation in the duodenum leads to trophozoite attachment
Results in malabsorption of protein and fat
Presentation: foul-smelling non-bloody diarrhoea, cramps, flatulence, NO fever

30

What are the main features of Cryptosporidium parvum?

Causes severe diarrhoea in the immunocompromised
Oocysts can be seen in the stool using modified Kinyoun acid fast stain
Rx: paromomycin