Gastrointestinal Cultures Flashcards
Differential media
Differentiation of bacterial species based on colony morphology
Selective media
- limit growth of normal flora
- enhance growth of pathogens
What does Hektoen grow?
Only gram (-)
SMAC plate color
Pink
E.coli colony color on XLD
Yellow
Salmonella colony color on XLD
Black
TCBS plate color
Green
What color colonies does Vibrio produce?
Yellow
Most commonly ID’d intestinal parasite in the US; contaminated water (mountain streams)
Giardia lamblia
Troph form can migrate to liver and cause liver abscess
Entamoeba histolytica
- resistant to chlorine
- public swimming pool outbreaks
- fecally contaminated food/water
- international produce
- p2p
Cryptosporidium parvum and C. hominid
- contaminated food, water, and produce
- mostly soon in travelers returning from endemic areas
Cyclospora
Cause of diarrhea in immunocompromised individuals, particularly patients with AIDS
Microsporidia
Which pathogens have longer incubation periods and make patients sicker longer?
Parasitic pathogens
How do you diagnose parasitic pathogens?
Physically exam stool OR antigen detection / serological kits
Does not cause diarrhea but is associated with peptic ulcer disease
Heliobacter pylori
- Food poisoning
- neurotoxin
Staphylococcus aureus / Bacillus cereus
Other bacterial pathogens
- Plesiomonas
- Aeromonas
- Edwardsiella
- Listeria monocytogenes
Viral GI pathogens
- Rotavirus
- Enteric adenovirus
- Calcivirus
- Astrovirus
What type of GI pathogen is rotavirus?
Viral
What type of GI pathogen is Enteric adenovirus?
Viral
What type of GI pathogen is Calcivirus?
Viral
What type of GI pathogen is Astrovirus?
Viral
Most common cause of diarrheal illness in children
Rotavirus
Causes GI infections
Enteric adenovirus
Norwalk virus / cruise ships
Calcivirus
Infections in very old and young
Astrovirus
GI parasitic infection
- Giardia lamblia
- Entamoeba histolytica
- Cryptosporidium parvum and C. hominis
- Cyclospora
- Microsporidia
Giardia lamblia is a:
GI parasitic infection
Entamoeba histolytica is a:
GI parasitic infection
Cryptosporidium parvum and C. hominis are:
GI parasitic infections
Cyclospora is a:
GI parasitic infection
Microsporidia is a:
GI parasitic infection
Collection of GI specimen
- nonpreserved stool
- fresh stool, qtip - spread thin layer on slide, wright stain - look for WBCs
- WBCs indicate inflammatory diseases
GI host defenses
-colon
IgA (antibody) produced fight off some organisms
Bacterial Pathogens of the GI tract
- Campylobacter jejuni
- Salmonella typhi
- Shigella sonnei
- Yersinia enterocolitica
- Vibrio cholera
- E.coli O157:H7
- Clostridium difficile
- Staphylococcus aureus and Bacillus cereus
- Heliobacter pylori
- Asromonas and Plesiomonas
Causes the most severe form of enteric fever: typhoid fever
Salmonella typhi
Humans are the only known host for this pathogen
Salmonella typhi
Spread by fecally contaminated food or water and causes an inflammatory response
Salmonella typhi
Bacteria survive the host immune cells so it is considered an intracellular pathogen
Salmonella typhi
Normal GI flora are predominantly what species?
Anaerobic
GI host defenses
-what does normal flora do?
Fights off pathogens
GI host defenses
-stomach acidity
Most pathogens never reach the intestines because of the acidic environment of the stomach
GI host defense
-intestines - peristalsis
Constant motion that pushes substances through the intestines and reduces chances for adherence
Mucous layer
GI host pathogen
Antibiotic associated diarrhea caused by drug disrupting the normal indigenous flora of the colon
Clostridium difficile
Produces exotoxins A and B, easily spread by fecal/oral route, spore and toxin producing
Clostridium difficile
Infections more common in winter months
Yersinia enterocolitica
Linked to meat, unpasteurized milk and other dairy products
Yersinia enterocolitica
Refrigeration does not prevent growth of the organism
Yersinia enterocolitica
Causative agent of cholera
Vibrio cholera
Fish and shellfish
Vibrio cholera
Known to produce “rice-water” stools, risk of death from dehydration
Vibrio cholera
Specific strain that causes shiga-like toxins
E.coli O157:H7
Is E.coli a normal inhabitant of the GI tract?
Yes
Some patients develop chronic colonization leading to persistent shedding of the organism with potential transmission to others (Typhoid Mary)
Salmonella typhi
The most common species in the US, one of the most easily communicable bacterial diarrheal pathogens
Shigella sonnei
Produces several toxins including shiga toxin which can have cytotoxic, enterotoxic and neurotoxic effects
Shigella sonnei
Antibiotics can delay clinical improvement
Shigella sonnei
Most common bacterial cause of gastroenteritis in the world
Campylobacter jejuni
Contaminated poultry
Campylobacter jejuni
What is Guillain-Barré syndrome?
Life-threatening neurological disease
What causes Guillan-Barre syndrome and reactive arthritis?
Campylobacter jejuni
