GI pathogens

Enterobacteriaceae Morphology?

Small Gram-negative rods.

Enterobacteriaceae Oxygen requirement?

Facultative anaerobes.

Enterobacteriaceae Motility?

Most are motile (exceptions: Shigella, Klebsiella).

Enterobacteriaceae Glucose fermentation?

Nearly all ferment glucose and other monosaccharides.

Enterobacteriaceae Nitrate reduction?

Reduce nitrate (NO3-) to nitrite (NO2-).

Enterobacteriaceae Oxidase test result?

Oxidase negative.

Triple Sugar Iron (TSI) Agar Purpose of TSI test?

Tests bacterial ability to ferment sugars and produce H2S or gas.

Triple Sugar Iron (TSI) Agar Key components?

Phenol red (pH indicator), lactose, sucrose, glucose, sodium thiosulfate, ferrous sulfate.

Triple Sugar Iron (TSI) Agar Result K/A?

Glucose fermentation only (yellow butt, red slant).

Triple Sugar Iron (TSI) Agar Result A/A?

Fermentation of lactose/sucrose and glucose (all yellow).

Triple Sugar Iron (TSI) Agar Black precipitate in TSI?

H2S production (iron sulfides formed).

Triple Sugar Iron (TSI) Agar Gas bubbles or splitting?

CO2 or H2 gas production.

Shigella spp. Morphology?

Gram-negative rods; closely related to E. coli.

Shigella spp. Oxygen requirement?

Facultative intracellular pathogen.

Shigella spp. Major species?

S. dysenteriae, S. flexneri, S. boydii, S. sonnei.

Shigella spp. Diseases caused?

Shigellosis (diarrhea to dysentery).

Shigella spp. Symptoms of dysentery?

Fever, abdominal pain, bloody and mucus-filled stool, and frequent defecation.

Shigella spp. Complication of S. dysenteriae type 1?

Hemolytic Uremic Syndrome (HUS): hemolytic anemia, thrombocytopenia, renal failure.

Shigella spp. Virulence factor?

Shiga toxin (Stx).

Shigella spp. Mechanism of Shiga toxin?

Cleaves 28S rRNA → inhibits protein synthesis → endothelial damage → kidney failure.

Shigella spp. Treatment?

Ciprofloxacin (5–7 days).

Shigella spp. Post-infectious sequelae?

Reiter’s syndrome (urethritis, conjunctivitis, arthritis).

Shigella – Laboratory Diagnosis MacConkey Agar?

No lactose fermentation (pale colonies).

Shigella – Laboratory Diagnosis XLD Agar?

No xylose fermentation (red colonies).

Shigella – Laboratory Diagnosis Gram stain appearance?

Small Gram-negative rods.

Shigella – Laboratory Diagnosis Motility?

Non-motile.

Escherichia coli Normal role?

Part of normal gut flora; produces vitamins B12 and K.

Escherichia coli Pathogenic types (pathovars)?

ETEC, EPEC, EHEC, EIEC, EAEC, UPEC.

Escherichia coli E. coli antigens?

O (LPS), H (flagella), K (capsule).

Uropathogenic E. coli (UPEC) Diseases?

Cystitis (bladder) and pyelonephritis (kidney).

Uropathogenic E. coli (UPEC) Virulence factors?

Type 1 pili (bladder colonization), P pili (kidney colonization).

Uropathogenic E. coli (UPEC) Lab tests?

Gram-negative rods; lactose fermentation (pink on MacConkey).

Uropathogenic E. coli (UPEC) Urease test?

Negative.

Uropathogenic E. coli (UPEC) Indole test?

Positive.

Uropathogenic E. coli (UPEC) Treatment?

Antibiotics (based on susceptibility).

Enterotoxigenic E. coli (ETEC) Main disease?

Traveler’s diarrhea, childhood diarrhea.

Enterotoxigenic E. coli (ETEC) Toxins?

Heat-labile (LT) and heat-stable (ST) enterotoxins.

Enterotoxigenic E. coli (ETEC) Mechanism?

Stimulate loss of water/electrolytes → watery diarrhea.

Enterotoxigenic E. coli (ETEC) Type of diarrhea?

Large-volume watery diarrhea.

Enteropathogenic E. coli (EPEC) Population affected?

Infants and young children.

Enteropathogenic E. coli (EPEC) Virulence factor?

Attaching and effacing (AE) lesions; destruction of microvilli.

Enteropathogenic E. coli (EPEC) Symptoms?

Persistent watery diarrhea.

Enteropathogenic E. coli (EPEC) Mortality?

High infant mortality in developing countries.

Enterohemorrhagic E. coli (EHEC) Main serotype?

O157:H7.

Enterohemorrhagic E. coli (EHEC) Reservoir?

Healthy cattle.

Enterohemorrhagic E. coli (EHEC) Transmission?

Undercooked beef, fecal-oral.

Enterohemorrhagic E. coli (EHEC) Virulence factor?

Shiga-like toxin (similar to S. dysenteriae Stx).

Enterohemorrhagic E. coli (EHEC) Symptoms?

Abdominal cramps, watery diarrhea (early), bloody diarrhea (late).

Enterohemorrhagic E. coli (EHEC) Complication?

Hemolytic Uremic Syndrome (HUS).

Enterohemorrhagic E. coli (EHEC) EHEC vs Shigella?

EHEC ferments lactose; Shigella does not.

E. coli Laboratory Diagnosis TSI result?

A/A, gas production, no H2S.

E. coli Laboratory Diagnosis Urease test?

Negative.

E. coli Laboratory Diagnosis Indole test?

Positive.

E. coli Laboratory Diagnosis MacConkey agar?

Lactose fermenter (pink colonies).

Salmonella enterica Morphology?

Gram-negative motile bacillus with peritrichous flagella.

Salmonella enterica Transmission?

Fecal-oral via poultry and dairy products.

Salmonella enterica Fermentation?

Does not ferment lactose.

Salmonella enterica TSI result?

K/A, gas, H2S positive.

Salmonella enterica Urease test?

Negative.

Salmonella enterica Indole test?

Negative.

Salmonella enterica Post-infectious sequelae?

Reiter’s syndrome.

Proteus species Morphology?

Gram-negative rods; motile; swarming motility on Blood agar with fishy odor.

Proteus species Most common species?

Proteus mirabilis and Proteus vulgaris.

Proteus species Infections?

Urinary tract infections (UTIs).

Proteus species TSI results?

P. mirabilis: K/A + H2S; P. vulgaris: A/A + H2S.

Proteus species Urease test?

Positive.

Proteus species Indole test?

P. mirabilis negative; P. vulgaris positive.

Campylobacter jejuni Morphology?

Gram-negative curved or spiral-shaped bacillus (“comma shaped”).

Campylobacter jejuni Motility?

Motile with peritrichous flagella.

Campylobacter jejuni requirement?

Microaerophilic (5% O2, 10% CO2).

Campylobacter jejuni Optimal growth temperature?

42°C.

Campylobacter jejuni Major source?

Poultry.

Campylobacter jejuni Disease?

Bloody diarrhea, fever, abdominal pain.

Campylobacter jejuni Post-infectious sequelae?

Guillain-Barré syndrome, Reiter’s syndrome.

Campylobacter jejuni Lab diagnosis?

CAMPY Blood Agar, 42°C incubation, microaerophilic, oxidase +, catalase +, hippurate +.

Helicobacter pylori Morphology?

Gram-negative, spiral or comma-shaped, highly motile.

Helicobacter pylori Oxygen requirement?

Microaerophilic.

Helicobacter pylori Site of infection?

Stomach (gastric mucosa).

Helicobacter pylori Diseases?

Chronic gastritis, peptic ulcers, gastric carcinoma.

Helicobacter pylori Virulence factors?

Urease, VacA (vacuolating toxin), mucinase.

Helicobacter pylori Function of urease?

Neutralizes stomach acid (NH3 + HCl → NH4Cl).

Helicobacter pylori Function of mucinase?

Degrades mucus layer; exposes epithelium to acid.

Helicobacter pylori Function of VacA?

Disrupts epithelial cells; promotes apoptosis and T-cell dysfunction.

Helicobacter pylori Lab diagnosis?

Skirrow’s medium (Blood agar + antibiotics), microaerophilic (5% O2, 10% CO2).

Helicobacter pylori Rapid Urease Test?

Positive (turns magenta/bright pink).

Helicobacter pylori Cancer association?

10–20% lifetime risk of ulcers; 1–2% risk of gastric cancer.

Watery diarrhea pathogens?

ETEC, EPEC.

Bloody diarrhea pathogens?

EHEC, EIEC, EAEC, Shigella, Campylobacter.

UTI pathogens?

UPEC, Proteus, occasionally Klebsiella.