Gastrointestinal Pathogen Highlights (Chapter 25)

Vocabulary-style flashcards covering the GI pathogens and key concepts from Chapter 25.

Fecal-oral route

Transmission of pathogens by ingestion of fecally contaminated food or water.

Enterotoxin

An exotoxin that targets the GI tract and can cause gastroenteritis.

Staphylococcus aureus enterotoxin-mediated gastroenteritis

Foodborne illness from preformed enterotoxin in contaminated food; onset 1–6 hours; vomiting and diarrhea; duration about 2–3 days.

Staphylococcus aureus refrigeration growth

Staph can multiply at refrigeration temperatures (4–6°C); refrigeration does not guarantee safety.

Vibrio cholerae (cholera)

Bacterium causing cholera; severe dehydration with rice-water stools; incubation ~3 days; high mortality if untreated; commonly waterborne; antibiotics indicated for treatment.

Salmonella enterica

Bacterium causing gastroenteritis; does not produce toxin; incubation 6–48 hours; duration 1–2 days; reptiles can be reservoirs.

Giardia lamblia

Protozoan with cyst and trophozoite life stages; low infectious dose (ID50) of 30–50 cysts; waterborne; incubation ~1 week; treated with Flagyl.

Giardia cyst

Dormant, hardy cyst shed in feces; ingested to initiate infection; excysts in the stomach to become trophozoites.

Giardia trophozoite

Replicating vegetative stage in the small intestine; possesses flagella and causes GI symptoms.

Giardia ID50

Infectious dose for 50% of immunocompetent hosts is about 30–50 cysts.

Cryptosporidium parvum

Protozoan with oocyst and trophozoite stages; oocysts are dormant and infectious; severe diarrhea; low ID50 (10–30 oocysts); many animal reservoirs.

Cryptosporidium oocyst

Dormant, highly resistant life stage; ingested to initiate infection and form trophozoites.

Cryptosporidium ID50

Infectious dose for 50% of immunocompetent hosts is about 10–30 oocysts.

Tapeworm (Beef tapeworm Taenia saginata)

Cestode transmitted via undercooked beef; cattle harbor cysts in muscle; humans ingest cysts; worms mature in the intestine and can cause malnutrition or obstruction.

Scolex

Head of a tapeworm with hooks and suckers used to anchor to the intestinal lining.

Proglottids

Tape-like segments of a tapeworm containing eggs; shed in feces and spread infection.

Cysts in beef muscle

Larval cysts (metacestodes) in cattle muscle; transmitted to humans by eating undercooked beef.

Roundworms (Ascaris lumbricoides)

Ingest eggs; larvae migrate to intestines and lungs; may cause mild GI symptoms or pneumonia-like symptoms in heavy infections.

Guinea worm disease (Dracunculus medinensis)

Parasitic infection acquired from water containing copepod larvae (water fleas); adult worm forms a blister and is slowly withdrawn; near eradication efforts by CDC.

Pinworms (Enterobius vermicularis)

Most common human parasite; eggs laid around the anus; infection common in children; eggs are easily spread and survive ~2 weeks; itching is a common symptom.

Scotch Tape method

Simple diagnostic test for pinworms: apply sticky tape to the perianal area and examine for eggs under a microscope.

Rice-water stool

Profuse, watery stool characteristic of cholera caused by Vibrio cholerae.