CH19 Enterobacterales

Yersinia pestis

• Only transmitted to humans through flea bites.

• not intestinal, causative agent of plague

Yersinia enterolitica

• foodborne

Escherichia coli

• Most Common Cause of Healthcare-associated Infections

• Leading Cause of CA UTI

• Highly diverse due to horizontal gene transfer (plasmids,transposons, bacteriophages)

• Pathogenic strains classified as intestinal or extraintestinal

Salmonella spp.

• foodborne

• intestinal pathogens

• cause of typhoid fever

Shigella spp.

• foodborne

• intestinal pathogen

• cause of dysentery

Opportunistic Pathogens (Citrus Enters K Professional Sir)

Citrobacter, Enterobacter, Klebsiella, Proteus, Serratia

• produce enterotoxins

Diuretic strains of E. coli

• ETEC (enterotoxigenic)

• EIEC (enteroinvasive)

• EPEC (enteropathogenic)

• EAEC (enteroaggregative)

• EHEC (enterohemorragic)

  • VTEC (verocytotoxin-producing)

  • STEC (Shigalike toxin-producing)

• DAEC (diffusive aggregative)

• AIEC (adherent invasive)

• DAEC (diffusive aggregative)

• AIEC (adherent invasive)

cause diarrheal illness

• ETEC (enterotoxigenic)

• EIEC (enteroinvasive)

• EPEC (enteropathogenic)

• EAEC (enteroaggregative)

express potent toxins and cause GI infections

• EHEC (enterohemorragic)

  • VTEC (verocytotoxin-producing)

  • STEC (Shigalike toxin-producing)

• systemic infections

E. coli Cultural Characteristics

• NA: circular, smooth, moist, grayish colonies

• MacConkey: Pink Colonies (lactose fermenter)

• EMB: Metallic Green Sheen (acidic fermentation)

E. coli Microscopic Morphology

• Motile

• Non-spore forming

E. coli Oxidase Test

• Oxidase - (no cytochrome c)

Intestinal Infection Strains of E. coli

ETEC, EPEC, EIEC, STEC, and EAEC

How can Intestinal Infections of E. coli be classified?

O and H antigen

O antigen

• Repeating polysaccharide chain of the LPS outer membrane

• Somatic

H antigen

• flagellar structure

What are the reservoirs of intestinal pathogenic E. coli?

Human and Animal intestines

Major Reservoir of STEC

Cattle

Transmission of E. coli (intestinal)

• Fecal-Oral

• Person-to-Person

• Ingestion of Undercooked Meat

E. coli Catalase Test

• Catalase + (breaks down H₂O₂)

E. coli IMViC Test

• Indole + (degrades tryptophan to indole)

• MR + (mixed acid fermentation)

• VP - (no acetoin)

• Citrate Utilization -

E. coli TSI Test

• TSI A/A (Ferments Glucose, Sucrose, Lactose, no H₂S)

Occurrence of Extraintestinal Infections of E. coli

when normal gut flora translocates to sterile body sites or via nosocomial spread.

Extraintestinal E. coli infections are common in

Long term

Leading Gram-negative for causing Extraintestinal Infections

E. coli

Associated Extraintestinal Infections

• UTI

• Abdominal and Pelvic Infections

• Pneumonia

• Bacteremia

• Meningitis

Virulence Factors of E. coli

endotoxin, capsule production, pili

ETEC Virulence

Pili, Heat-labile (LT), Heat-stable (ST) enterotoxins

ETEC Infections

Traveler and Childhood diarrhea

EIEC Virulence

Invades Enterocytes

EIEC Infecrtion

Dysentery in Young Children due to poor sanitation

EPEC Virulence

Bundle-forming pilus, intimin (changes cell surface)

EPEC Infection

Diarrhea in infants of low income nations

STEC Virulence

Shiga like toxin (S. dysenteriae)

Associated with E. coli O157:H7

STEC Disease

Inflammation and bleeding of the mucosa of the large intestine

(i.e., hemorrhagic colitis), hemolytic uremic

syndrome

Transimitted by undercooked ground beef or raw

milk.

EAEC Virulence

Pili, ST-like, hemolysin-lyke toxins

EAEC Infections

Watery Diarrhea