Microbiology of the Gastrointestinal Tract

Introduction• GI defenses• Normal flora

Mouth and Esophagus• Dental infections• Candida infection

Stomach• Helicobacter infection

Intestine• Food poisoning• Non-food-related diarrhea

LECTURE OUTLINE

Food Poisoning

• Main bug details• gram stain, morphology

• pathogenic features

• food of choice

• Clinical setting

• Diagnosis

• Frequency of food poisoning is increasing!• more fresh fruit/vegetables• more pre-cooked foods• more kinds of food

• 5,000 deaths, 325,000 hospitalizations, 76 million illnesses

• FDA resources can’t keep up!

Food Poisoning

E. coli

Clostridium

Staphylococcus

Campylobacter

Yersinia

Listeria

Vibrio

Salmonella

Bacillus

Eating

Contaminated

Stuff

Causes

You

Lots of

Very

Smelly

Barf

Food Poisoning

• Staphylococcus• Salmonella• Shigella• Campylobacter• E. coli• Yersinia• Vibrio• Bacillus• Listeria• Clostridium

The bugs:

Food Poisoning

• gram-positive cocci

• enterotoxins • made in food• survive high temps

• nose, skin

Staphylococcus

Food Poisoning

Staphylococcus on blood agar plate

Staphylococcus

Staphylococcus surrounding hair shaft

• gram-negative rod• motile • injects proteins, causing “ruffles”• replicates in host cells• sensitive to stomach acid

Salmonella

Food Poisoning

Salmonella

Salmonella

Ruffles

Ruffles

Ruffles

• gram-negative rod• microaerophilic • likes warm places• C. jejuni (diarrhea), C. fetus (sepsis)• cells eat bugs, then die• monocytes can carry bugs into blood

Campylobacter

Food Poisoning

Campylobacter

Campylobacter

• gram-negative rod• motile • EHEC strains• O and H antigens• cytotoxins damage vessels

E. coli

Food Poisoning

E. coli

E. coli outbreak: raw spinach

• October 2006

• 3 died, over 200 became ill

• Traced to spinach grown in central California

• Grazing deer or water contaminated with cattle feces

E. coli outbreak: Taco Bell

• November-December 2006

• 70+ became ill

• Green onions vs. lettuce

• Contamination at packing plant?

• Diarrhea• Hemolytic uremic syndrome (HUS)

E. coli diseases

Food Poisoning

hemorrhagic colitis

Microangiopathic hemolytic anemia

• gram-negative rod• grows in cold temperatures • mesenteric lymphadenitis

Yersinia

Food Poisoning

Yersinia

Yersinia: “safety-pin” appearance

Plague

Y. pestis transmitted by tick

mesenteric lymphadenitis

mesenteric lymphadenitis

mesenteric lymphadenitis

• gram-negative rod• single flagellum • likes water• can tolerate acid• makes toxins

Vibrio

Food Poisoning

Vibrio

Vibrio

• gram-positive rod• spores • makes toxins (in food)

Bacillus

Food Poisoning

Bacillus

Bacillus: “box-car” appearance

Bacillus

• gram-positive rod• heat resistant• hides out in host cell cytoplasm• mild GI illness in most• meningitis, sepsis in fetuses, elderly

Listeria

Food Poisoning

Listeria

Listeria inside neutrophil

• gram-positive rod• anaerobic• spores• toxins• C. botulinum: progressive paralysis

• adults usually recover• babies may not

• C. perfringens: diarrhea

Clostridium

Food Poisoning

Clostridium

Clostridium

Clostridium

Clostridium

before after

Botox

• enterocolitis• self-limited, usually• serious complications rare• incubation time varies• fever, tenderness on exam

Clinical

Food Poisoning

• culture• gram stain• other tests

Diagnosis

Food Poisoning

Introduction• GI defenses• Normal flora

Mouth and Esophagus• Dental infections• Candida infection

Stomach• Helicobacter infection

Intestine• Food poisoning• Non-food-related diarrhea

LECTURE OUTLINE

• Important cause of death worldwide

• Here, more bothersome than deadly

• Three categories: • secretory diarrhea• invasive diarrhea• antibiotic-associated diarrhea

Non-Food-Related Diarrhea

• loss of fluids, electrolytes from small intestine

• mild (traveler’s diarrhea) to severe (cholera)

Definition

Secretory Diarrhea

• Enterobacteriaceae (E. coli, others)

• Vibrionaceae (Vibrio, Campylobacter)

Pathogens

Secretory Diarrhea

• environment (vibrio)

• humans (salmonella)

Reservoirs

Secretory Diarrhea

Transmission

• fecal-oral route

• … feces, food, fluids, fingers, flies, fomites, fornication

• some bugs require only a small inoculum!

• No matter how clean we think we are…if sh*t was red, the world would be pink.

Secretory Diarrhea

Pathogenesis

• proximal small intestine• different bugs have different mechanisms

Secretory Diarrhea

V. cholerae

• virulence genes switch on in intestine• cholera toxin binds to epithelium, gets eaten• toxin activates adenylate cyclase cAMP → Na+ absorption, Cl- excretion• water moves into gut by osmosis, leading to diarrhea

Secretory Diarrhea

normal enterocyte enterocyte in secretory diarrhea

ETEC

• Enterotoxins change fluid transport in the gut…• …so instead of absorbing, the gut is secreting.• like cholera toxin, but less serious

Secretory Diarrhea

EPEC

• complex mechanisms – no toxin

• actin-rich pedestals

• beyond that, unclear mechanisms

Secretory Diarrhea

Clinical

• most cases acute, self-limiting• except V. cholera and EPEC illnesses,

which can be fatal

Secretory Diarrhea

Stool culture

• selective media• differential media Further testing

• strains, virulence factors• useful for epidemiology

Secretory Diarrhea

Treatment

• usually not necessary• except for which diseases?

Secretory Diarrhea

Definition

• cause: bugs that invade the intestine• result: bloody diarrhea or dysentery• bugs: Shigella and EHEC

Invasive Diarrhea

Shigella: characteristics

• gram-negative rod

• species: S. dysenteriae (dysentery) S. flexneri S. boydii S. sonnei (secretory diarrhea)

Invasive Diarrhea

Shigella

Shigella

Shigella: transmission

• person-to-person

• small inoculum!

Invasive Diarrhea

Shigella: pathogenic features

• changeable phenotype!• Acid-resistant in stomach, invasive in intestine• Pure selfishness: whatever works best. • Acidity turns on the genes for acid resistance!

Invasive Diarrhea

• Approach.

• Sneakiness.

• Eating.

• Prodding.

• Escape.

• Finger.

• Ulcer.

Shigella: pathogenic features

Invasive Diarrhea

Shigella

• Shiga toxin stops protein synthesis• decreases Na+ absorption (watery stools)• damages endothelial cells (bloody stools)• worst result: HUS

Shigella: toxin

Invasive Diarrhea

Diseases caused by E. coli:

• Diarrhea• Urinary tract infection• Neonatal sepsis• Gram-negative sepsis

E. coli transmitted in DUNG-contaminated water

Invasive Diarrhea

Enterohemorrhagic E. coli (EHEC): characteristics

• gram-negative rod

• many strains cause invasive diarrhea

• O (cell wall) and H (flagellar) antigens

• O157:H7 most common

Invasive Diarrhea

EHEC: transmission

• food (beef, spinach, green onions…)

• small inoculum!

Invasive Diarrhea

hemorrhagic colitis

microangiopathic hemolytic anemia

EHEC: pathogenic features

• toxins (inactivate RNA, like Shiga toxin)• endothelial damage (toxin + cytokines)• end result: bloody diarrhea and/or HUS

Invasive Diarrhea

EHEC: diseases• GI complications

• sometimes, asymptomatic• often, bloody diarrhea (hemorrhagic colitis)• usually resolves in a week

• HUS• 1 in 10 people with severe diarrhea get HUS• #1 cause of acute renal failure in children• triad: MAHA, thrombocytopenia, renal failure• can be fatal (especially in children, elderly)

Invasive Diarrhea

Diagnosis

• stool exam

• stool culture

• fancy stuff

Invasive Diarrhea

• Common in hospitalized patients!

• Broad-spectrum antibiotics:• reduce normal flora• interfere with carb breakdown

• Clostridium difficile underlies most cases

Antibiotic-Associated Diarrhea

Mnemonic for C. difficile infection:

It’s difficult to be in a closet with someone having

explosive foul-smelling diarrhea,

because it smells and there is no air in there.

Antibiotic-Associated Diarrhea

Bug characteristics

• gram-positive rod

• obligate anaerobe

• forms spores

• hard (‘difficile’) to grow!

• makes exotoxins

Antibiotic-Associated Diarrhea

Clostridium

Pathology

• exotoxins cause cell death, shallow ulcers, pseudomembranes

• early lesions superficial

• may eventually invade

Antibiotic-Associated Diarrhea

Pseudomembranous colitis

Epidemiology

• 30% of hospitalized patients!

• elderly at greater risk

• associated with antibiotics

• also with chemotherapy, enemas, enteric feeding

• spread patient to patient by hospital personnel

Antibiotic-Associated Diarrhea

Disease severity

• wide spectrum

• asymptomatic to fulminant colitis

• usually: just diarrhea

• amount of toxin is unrelated

Antibiotic-Associated Diarrhea

Forms of disease

• Diarrhea

• Pseudomembranous colitis

• Osmotic diarrhea

• Fulminant colitis

Antibiotic-Associated Diarrhea

Diagnosis

• stool smear

• forget culture

• toxin detection

• scope dangerous

Antibiotic-Associated Diarrhea

Treatment

• oral metronidazole

• vancomycin

• relapse: metronidazole

• severe disease: bowel resection

Antibiotic-Associated Diarrhea