Microbiology chapter 25
What is the 2nd most common illness category in the U.S.?
Digestive system diseases (mostly fecal‑oral transmission).
What breaks the fecal‑oral cycle?
Proper sewage disposal, water disinfection, and safe food handling.
Where are the highest bacterial counts in the GI tract?
Large intestine (>100 billion/g; up to 40% of fecal mass is bacteria).
Why do the stomach and small intestine have few microbes?
Acidity of the stomach.
What organism is the primary cause of dental caries?
Streptococcus mutans — forms dextran from sucrose; produces lactic acid → enamel destruction.
Which sugars do NOT promote caries?
Starch, mannitol, sorbitol (not used to make dextran).
What is gingivitis vs periodontitis?
What causes acute necrotizing ulcerative gingivitis (“Trench Mouth”)?
Prevotella intermedia + spirochetes (Borrelia vincentii).
Infection vs intoxication — key differences?
What is dysentery?
Severe diarrhea with blood or mucus.
What food poisoning toxin is heat‑stable (not destroyed by boiling 30 min)?
Staph aureus enterotoxin.
Classic foods for Staph food poisoning?
Custards, cream pies, ham (high osmotic pressure).
What Shigella species produces Shiga toxin and causes severe dysentery?
Shigella dysenteriae.
What finding suggests invasive diarrhea (not toxin‑mediated)?
WBCs in stool.
Common sources of Salmonella?
Chicken and eggs.
What causes fever in Salmonella gastroenteritis?
Endotoxin.
What organism causes typhoid fever?
Salmonella typhi — human‑only pathogen.
Who is the classic chronic carrier?
Typhoid Mary (gallbladder colonization).
What does cholera toxin do?
Activates secretion of Cl⁻ and HCO₃⁻, causing massive watery diarrhea. Mortality untreated: 50%.
What foods are associated with V. parahaemolyticus and V. vulnificus?
What strain causes hemorrhagic colitis and HUS?
E. coli O157:H7 — produces Shiga‑like toxin.
What is the 2nd most common cause of diarrhea in the U.S.?
Campylobacter jejuni.
What syndrome is associated with Campylobacter?
Guillain‑Barré syndrome.
What enzyme allows H. pylori to survive stomach acid?
Urease → produces ammonia.
What foods commonly cause C. perfringens gastroenteritis?
Meats left at room temperature (spores germinate).
What food is classically associated with B. cereus?
Fried rice. Two toxins:
What gland is swollen in mumps?
Parotid glands. Orchitis may occur in post‑pubertal males.
Which hepatitis viruses are fecal‑oral?
Hepatitis A virus , Hepatitis E virus
Which hepatitis requires HBsAg to infect?
Hepatitis D (HDV) — coinfection or superinfection.
Which hepatitis is most associated with chronic infection and cirrhosis?
HCV (slow, progressive liver damage).
Most common cause of viral gastroenteritis in children?
Rotavirus.
What virus causes outbreaks on cruise ships?
Norovirus (Norwalk agent) — highly infectious, hardy.
What protozoan causes foul‑smelling, greasy diarrhea?
Giardia lamblia — cysts resist chlorine; treat with metronidazole.
What stain identifies Cryptosporidium oocysts?
Acid‑fast stain (oocysts stain red).
What foods commonly transmit Cyclospora?
Imported berries and produce.
What organism causes amoebic dysentery?
Entamoeba histolytica — eats Red blood cells ; can cause liver abscess.
Which tapeworm causes neurocysticercosis?
Taenia solium (pork tapeworm).
What organism causes hydatid cysts?
Echinococcus granulosus — dog definitive host; sheep intermediate. Cysts can reach 15 liters; rupture → anaphylaxis.
How is Enterobius vermicularis diagnosed?
Tape test (perianal eggs).
How do hookworms infect?
Larvae penetrate skin → blood → lungs → swallowed → intestine. Causes iron‑deficiency anemia + pica.
What is the migration pattern of Ascaris lumbricoides?
Eggs → intestine → blood → lungs → throat → swallowed → intestine. Adults up to 1 foot long.
What causes trichinosis?
Trichinella spiralis — larvae encyst in muscle (esp. diaphragm, eye). Symptoms: fever, periorbital edema, myalgia, eosinophilia.