Enterobacteriaceae - Microbiology - Lecture Slides, Slides of Microbiology

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Enterobacteriaceae

Morphology & Identification

• Gram-negative non-spore forming rods. When motile, by peritrichous flagella.
• Primarily normal flora of gastrointestinal tract. E. coli > Klebsiella > Proteus > Enterobacter
• Free living, also transient colonizers of skin.
• Facultative anaerobes: mixed acid fermentation
• All ferment glucose; all reduce nitrates to nitrites; all oxidase negative.
• Lactose fermentation: normal flora positive and pathogens negative.
• Primary isolation media include eosin-methylene-blue (EMB) and MacConkey agar.
• Differential selective media for specific organisms including dyes and bile salts. (Salmonella-Shigella (SS) medium, bismuth sulfite media.)

Antigenic Structure

• Most are motile by peritrichous flagella --H antigens.
• Capsule – K antigen ( Vi for Salmonella).
• Cell envelope (wall)
• LPS (endotoxin) – O antigen.
• various outer membrane proteins.
• Pili - various antigen types, some encoded by plasmids

• septicemia,
• pneumonia,
• meningitis
• urinary tract infections

Citrobacter Enterobacter Escherichia Hafnia Morganella Providencia Serratia

Opportunistic diseases

- Enterobacteriaceae

• Histocompatibility antigen (HLA) B
  • Enterobacteriaceae
    • Salmonella
    • Shigella
    • Yersinia
• Not Enterobacteriaceae

• Campylobacter
• Chlamydia

Reiter's syndrome

• community acquired
• otherwise healthy people
  • Klebsiella pneumoniae
    • respiratory diseases
    • prominent capsule
  • urinary tract infection
    • fecal contamination
    • E. coli
    • Proteus
      • urease (degrades urea)
      • alkaline urine

Enterobacteriaceae

• E. coli
  • lactose positive
  • not usually identified
  • lactose positive sp. common, healthy intestine
• Shigella , Salmonella , Yersinia
  • lactose negative
  • identified

Feces

• other sites
  • identified biochemically

Enterobacteriaceae

Escherichia coli

• Toxins: two types of enterotoxin; Shiga-type toxin; Enteroaggregative ST-like toxin; Hemolysins; Endotoxin
• Type III secretion system
• Adhesions – colonization factors ; both pili or fimbriae ;non-fimbrial factors involved in attachment. There are at least 21 different types of adhesions.
• Virulence factors that protect the bacteria from host defenses: Capsule/Iron capturing ability (enterochelin)
• Outer membrane proteins

E.coli-Meningitis and Sepsis

• Neonatal meningitis – is the leading cause of

neonatal meningitis and septicemia with a

high mortality rate. Usually caused by strains

with the K1 capsular antigen.

Enterotoxigenic E. coli

• A watery diarrhea, nausea, abdominal

cramps and low-grade fever for 1-5 days.

• Travellers diarrhea and diarrhea in

children in developing countries

• Transmission is via contaminated food or

water.

Enterotoxigenic E. coli

• diarrhea like cholera
• milder
• nursery travellers diarrhea
• caused by LT, ST, or LT/ST.

E.coli-Enteroinvasive (EIEC)

• The organism attaches to the intestinal mucosa via

pili

• Outer membrane proteins are involved in direct

penetration, invasion of the intestinal cells, and destruction of the intestinal mucosa.

• There is lateral movement of the organism from

one cell to adjacent cells.

• Symptoms include fever,severe abdominal cramps,

malaise, and watery diarrhea followed by scanty stools containing blood, mucous, and pus.

• resembles shigellosis

Enteroinvasive E. coli (EIEC)

• Dysentery
  • resembles shigellosis
  • elder children and adult

diarrhea