PBL: Gastrointestinal Cultures Flashcards
Anatomical regions of the GI tract
- Oral cavity
- Esophagus
- Stomach (few bacteria b/c of ↓ pH)
- Small intestine (duodenum, jejunum, ileum)
- Large intestine
- Colon (cecum, ascending, transverse, descending)
- Sigmoid
- Rectum
List the members of normal adult bowel flora
99.9% anaerobes
- Bacteroides fragilis group
- Clostridium spp
- Bifidobacterium spp
- Anaerobic cocci
- Fusobacterium spp
Aerobes
- E. coli
- Other Enterobacteriaceae
- Enterococcus spp
Collection and transport for stool specimens
- Stool in a sterile cup or rectal swab
- In the absence of preservative, the sample is only viable for an hour after collection time
- If placed in preservative (Carey-Blair or buffered glycerol) the sample is viable for 48 hours
What preservative is not acceptable for Vibrio cultures?
Buffered glycerol
What media must all stool cultures be plated on?
- SBA
- MAC
- SMAC
- HEK
- Charcoal CAMPY
What media is available upon the physician’s request?
- TCBS
- YSA/CIN
What stool pathogens must be serologically typed after they’re identified in the lab?
Shigella and Salmonella
V. cholerae
- Appearance on TCBS
Yellow colonies (sucrose fermenter)
V. parahaemolyticus
- Appearance on TCBS
Green colonies (non-sucrose fermenters)
Shigella
- Appearance on HEK, MAC
- HEK: green/clear
- MAC: clear
E. coli 0157:H7
- Appearance on SMAC
Clear (sorbitol negative)
Salmonella
- Allearance on HEK, MAC
- HEK: black (H2S production)
- MAC: blear
Yersinia
- Media to set up
YSA/CIN or MAC
- Incubate at 25°C
C. jejuni
- Media to set up
Campy BAP
- ↑ CO2, ↓ O2, 42°C
C. difficile
- Media to set up
CCFA
H. pylori
- Tests
Biopsy, CLO test
Purpose of serotyping
- Useful in tracking an outbreak to its original source
- Aids in diagnosis and is required before identification is made
What media should serological typing be done on?
Sheep BPA
Which stool specimen must be submitted to the IN State Department of Health for confirmation?
Salmonella
Clinical signs of dehydration
- Dry or sticky mouth
- Low urine amount/color change
- “Skin tenting”
- Hypotension
- Sunken eyes
- Fatigue
- Rapid heartbeat
- Abnormal electrolytes
Clinical signs of severe dehydration
- Alteration in mental status
- Organ dysfunction (e.g., renal failure)
- Fever (indicates invasive pathogen)
- Rapid breathing
Two types of pathogenic mechanisms that contribute to organisms’ pathogenesis of GI illness
- Enterotoxin-mediated diarrhea (pre-formed in food)
- Diarrhea-mediated by invasion of bowel mucosal surface (infection)
Pathogens that cause diarrhea-mediated by invasion of bowel mucosal surface
- Shigella
- Salmonella
- Campylobacter jejuni
- Vibrio spp
Which pathogens cause non-bloody, watery stool (no RBCs, no WBCs, no mucus)
- S. aureus
- C. perfringens
- B. cereus
- B. botulinum
Which pathogens cause symptoms w/in minutes to hours (intoxication)?
- S. aureus
- C. perfringens
- B. cereus
- B. botulinum
Which pathogens cause symptoms ≥1 day?
- Shigella
- Salmonella
- C. jejuni (2-3 days)
- Vibrio spp.
What causes peptic ulcers?
H. pylori
What causes appendicitis-like illness esp. in children?
Y. enterocolitica
What causes HUS?
E. coli 0157:H7
What causes sepsis?
V. vulnificus or S. typhii
- Positive blood culture
What causes Guillan-Barre syndrome?
C. jejuni
What causes pseudomembranous colitis?
C. difficile
The gallbladder is a carrier state for what?
S. typhii
GNRs found in GI
- Shigella
- E. coli
- Salmonella
- Y. enterocolitica
- Vibrio spp. (curved, comma)
- C. jejuni (curved, S-shaped)
- P. shigelloides (straight/coccobacillary)
- Aeromonas spp (straight/coccobacillary)
- H. pylori (spiral)
GPRs found in GI
- Listeria (small)
- C. difficile (large; spores)
What does the presence of RBCs in a Wright stain examination indicate?
Bleed in intestinal wall
What does the absence of RBCs or pus in a Wright stain examination indicate?
Toxin-mediated illness → E. coli, V. cholerae, S. aureus, C. perfringens, B. cereus
What does the presence of WBCs in a Wright stain examination indicate?
Inflammatory diarrhea
What does the absence of WBCs in a Wright stain examination indicate?
Doesn’t rule out pathogen b/w 10-15% of stools that yield an invasive bacterial pathogen have an absence of fecal leukocytes
If there are WBCs and RBCs present in a Wright stain examination, what pathogens may be present?
- Salmonella
- Shigella
- Yersinia
- Campylobacter
- EIEC
- Vibrio spp
Campylobacter jejuni
- Source
- Disease
- Source: food (esp. chicken)
- Disease: Guillen-Barre
Salmonella
- Source for gastroenteritis and food poisoning
- Food: contaminated meat, poultry eggs, dairy products, farmed fish and shellfish
- Animals: turtles, iguanas, chickens
Salmonella
- Source for enteric/typhoid fever
Ingestion of fecally-contaminated food or water
Shigella
- Source
- Infected food or water (esp. salads and sandwiches prepared by hand)
- Person-to-person contact (daycares)
- Fecal-oral route (dysentery)
E. coli
- Source
- Coming into contact w/ human or animal feces
- Consumption of hamburger meat or unpasteruized milk
Vibrio spp
- Source
Shellfish, salt water
Y. enterocolitica and pseudotuberculosis
- Source
- Disease
- Meat, unpasteurized milk and other dairy products, chitterlings (intestines)
- Appendicitis-like illness esp. in children
C. difficile
- Source
- Disease
- Antibiotic-associated; nosocomial; normal flora but can be bad
- Pseudomembranous colitis
Listeria monocytogenes
- Source
Deli meats, hot dogs, unpasteurized dairy products
H. pylori
- Source
- Disease
- Fecal-oral or oral-oral routes
- Peptice ulcers
Plesiomonas and Aeromonas
- Source
- Disease
- Ingestion of contaminated water or raw shellfish
- Both cause gastroenteritis
- Oxidase positive
Causative agents of toxin-mediated food poisoning (intoxication)
- S. aureus (food handlers)
- B. cereus (fried rice)
- C. perfringens (meats, gravy)
- C. botulinum (homecanned)
Non-inflammatory self-limiting condition characterized by rapid onset of water, non-bloody diarrhea w/ NO FEVER
ETEC
ETEC produces what toxins?
- Heat stable toxin
- Heat labile toxin
Helps stimulate the secretion of fluid into the intestinal lumen
Heat stable toxin
Leads to hypersecretion of both fluids and electrolytes into the intetsinal lumen, causing watery diarrhea
Heat labile toxin
ETEC
- Patient populations
- 2nd leading cause of death in children < 5 years old, esp. in infants in developing countries
- Traveler’s diarrhea
How does ETEC cause infection?
Bacteria colonize mucosal surface of small intestine by using fimbriae to bind to cells of small intestine. Allows for the release of either one or both enterotoxins produced by ETEC bacterial cells
Causes a persistant condition of water, non-bloody diarrhea w/ mucus, often accompanied w/ a low-grade fever
EPEC
How does EPEC cause infection?
Serogroups bind to epithelial surface of small intestine using adhesin which causes a change in intestinal cell’s structure through the destruction of microvilli
Patient populations affected by EPEC
- Mostly affects infants, w/ diarrheal outbreaks occurring in hospital nurseries and daycare centers
- Rarely affects adults
Highly INVASIVE pathogen closely related to Shigella, which can directly penetrate the intestinal mucosa cells, causing high fever and profuse diarrhea w/ possible blood and mucus
EIEC (INVASIVE!)
How is EIEC transmitted?
Fecal-oral route
Patient populations affected by EIEC
Can occur in either children or adults
Major cause of foodborne illness and often involves watery diarrhea that progresses to bloody
EHEC, STEC, VTEC
For identification of EHEC, STEC, and VTEC plate it on ____
SMAC (negative)
Patient populations affected by EHEC, STEC, VTEC
Any age, but young children < 5 and the elderly are more likely to develop severe illness or HUS
Symptoms of HUS
- Acute renal failure
- Hemolytic anemia
- Thrombocytopenia
Besides setting up a SMAC plate for identifying E. coli O157:H7, why do we need to set up a shiga toxin test?
E. coli O157:H7 produces a verotoxin, which are shiga-like toxins (SMAC +)
Who does EAEC cause infection?
Adheres to the surface of the intestine, but in a clumped or aggregative manner, which triggers an increase in muus production
EAEC
- Patient populations
Pediatic population in developing countries as well as travelers
