Diagnosis of GIT

Question 1

What families of bacteria cause gastroenteritis

Answer 1

Enterobacteriaceae and Vibrionaceae

Question 2

What species are in enterobacteriaceae

Answer 2

Escherichia coli, Salmonella spp., Shigella spp, yersinia entercolitica

Question 3

What Genus are in Vibrionaceae?

Answer 3

Vibrio cholerae, virbrio parahaemolyticus, campylobacter

Question 4

What are the characteristics of enterobacteriaceae?

Answer 4

gram negative rods, facultative anaerobes, grow on simple media (MAC and NA), oxidase negative, fermentative metabolism of glucose, can be motile

Question 5

What are the characteristics of Vibrio?

Answer 5

gram negative curved rods, oxidase positive, motile (flagella), need 1% salt in media, fermentative metabolism

Question 6

What are the characteristics of campylobacter

Answer 6

gram negative curved rods, oxidase positive, motile (flagella), microaerophilic (O2 at 5%-10%), needs enriched media (blood), oxidative metabolism

Question 7

What is in MacConkey Agar and why?

Answer 7

Selective (bile salts) and indicator (neutral red and lactose) medium
Lactose fermenters produce acid that turn the media pink
Lactose non-fermenters produce alkali metabolites and turn the media yellow
routine medium

Question 8

Deoxycholate Citrate Agar

Answer 8

Selective indicator medium, contains bile salts, citrate (which inhibits E. Coli growth), neutral red and lactose
Same colour system as MAC
Also contains sodium thiosulphate that indicates the presence of H2S producers > may produce colonies with central black dots

Question 9

Selenite broth

Answer 9

enrichment medium for Salmonella spp. > may see red brick precipitate if present
contains sodium biselenite > inhibits growth of many g- and g+ bacteria

Question 10

B.cereus selective media

Answer 10

Indicator and diagnostic medium for bacillus cereus
B. cereus produces a blue precipitate because it cannot digest mannitol, and a white precipitate when it hydrolyses egg yolk lectin

Question 11

Campylobacter Medium (CAMP)

Answer 11

selective and enriched. contains blood, pyruvate, vitamin B6, antibiotics (vancomycin, polymyxin, trimethoprim)
campylobacter show as shiny colonies along streak lines of the plate
incubated at 42 C, 48 hrs, 5% O2 (microaerophilic conditions)
NOT DIAGNOSTIC

Question 12

What are some specialist medium?

Answer 12

B.cereus selective media, campylobacter medium, baird parker medium

Question 13

Baird Parker Medium

Answer 13

Highly specific selective and diagnostic (Staphylococcus aureus)
Contains: egg yolk emulsion, selective agents (tellurite, pyruvate, lithium)
Signs of staphylococcus
- shiny black colonies from reduction of tellurite
- narrow white clearing around colonies from lipase activity
further clear zone from proteolysis

Question 14

What is phage typing?

Answer 14

Tests susceptibility of bacteria to a panel of bacteriophages
Panel of phage dotted on lawn culture, read pattern of lysis

Question 15

How is PCR used for diagnostic testing

Answer 15

is used to determine presence of virulence factors. Uses a promoter that is specific to the virulence gene, amplification will only occur if gene is present

Question 16

What are the signs of intoxication by Staphylococcus aureus?

Answer 16

Short IP: 2-6 hr
Toxin: very small quantity causes illness, toxin in poop very good sign
Bacteria: on normal microbiota so not necessarily good indicator if found
symptoms: vomiting
often in high fatty, salty, sugary foods, at room temp

Question 17

What are the signs of emetic bacillus cereus intoxication?

Answer 17

short IP: 1-5hrs
associated with rice/starchy foods
> spores contaminate food, survive boiling, germinate during slow cooling and produce toxin
symptoms: vomiting, cramps, sometimes diarrhoea

Question 18

Bacillus cereus: diarrhoeal type

Answer 18

long IP: 6-15 hrs
spores survive and germinate post cooking, produces heat labile toxin in intestine (haemolysin BL or enterotoxin Nhe) > intestinal fluid secretion by activation of adenylate cyclase enzymes

Question 19

Signs of Clostridium perfringens infection

Answer 19

longer ip: 6-24 hrs
spores found in soil, gut of animals, dust
survives cooking and multiply when cooling at RT
spores sporulate in the stomach and release heat labile enterotoxin in intestine > inhibits glucoe transport, damages intestinal epithelium, causes protein loss into lumen
watery diarrhoea