Diagnosis of GIT Flashcards
What families of bacteria cause gastroenteritis
Enterobacteriaceae and Vibrionaceae
What species are in enterobacteriaceae
Escherichia coli, Salmonella spp., Shigella spp, yersinia entercolitica
What Genus are in Vibrionaceae?
Vibrio cholerae, virbrio parahaemolyticus, campylobacter
What are the characteristics of enterobacteriaceae?
gram negative rods, facultative anaerobes, grow on simple media (MAC and NA), oxidase negative, fermentative metabolism of glucose, can be motile
What are the characteristics of Vibrio?
gram negative curved rods, oxidase positive, motile (flagella), need 1% salt in media, fermentative metabolism
What are the characteristics of campylobacter
gram negative curved rods, oxidase positive, motile (flagella), microaerophilic (O2 at 5%-10%), needs enriched media (blood), oxidative metabolism
What is in MacConkey Agar and why?
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
Deoxycholate Citrate Agar
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
Selenite broth
enrichment medium for Salmonella spp. > may see red brick precipitate if present
contains sodium biselenite > inhibits growth of many g- and g+ bacteria
B.cereus selective media
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
Campylobacter Medium (CAMP)
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
What are some specialist medium?
B.cereus selective media, campylobacter medium, baird parker medium
Baird Parker Medium
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
What is phage typing?
Tests susceptibility of bacteria to a panel of bacteriophages
Panel of phage dotted on lawn culture, read pattern of lysis
How is PCR used for diagnostic testing
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
What are the signs of intoxication by Staphylococcus aureus?
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
What are the signs of emetic bacillus cereus intoxication?
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
Bacillus cereus: diarrhoeal type
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
Signs of Clostridium perfringens infection
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