E. Coli

• Enterobacteriaceae

  The most common group of gram-negative rods cultured in clinical laboratories both as normal flora and as agents of disease
• Along with staphylococci and streptococci, Enterobacteriaceae are the most common bacteria that cause disease
• Enterobacteriaceae


  A large diverse family of bacteria that exhibit a considerable degree of relatedness
• Revisions in bacterial taxonomy and nomenclature, and recognition and acknowledgement of novel bacteria are published in the International Journal of Systematic and Evolutionary Microbiology

  
• Enterobacteriaceae

  • Gram-negative bacilli
  • Non-spore-forming
  • Most are motile (peritrichous); Plesiomonas has lophotrichous flagellation; some are nonmotile (Klebsiella; Shigella; Yersinia at 35-37 oC, motile at room temperature)
  • Some are encapsulated (Klebsiella), others are non-encapsulated
  • Facultative anaerobes
  • Are oxidase negative, EXCEPT Plesiomonas
  • Ferment glucose but otherwise vary in the utilization of other carbohydrates
  • Most reduce nitrates to nitrites
• O antigen (somatic antigen)


  Associated with the outer membrane (OM) of the cell wall found in all species of enteric bacilli; Repeating units of polysaccharides that consist the outer region of the lipopolysaccharides (LPS); Heat-stable, i.e., the bacteria keep their immunogenicity, agglutinating, and antibody-binding capacity after boiling; Alcohol-stable
• K antigen (capsular antigen or fimbrial antigen)


  Mostly associated with the capsule (others are associated with the fimbriae) found in some, not all, enteric bacilli; Polysaccharides (capsular) or proteins (fimbrial) in nature; Heat-labile, that is inactivated by boiling
• H antigen (flagellar antigen)


  Found in the flagella of motile enteric bacilli; Consists of proteins; Heat- and alcohol labile
• Serotyping

  Bacterial suspension in saline is mixed with a solution of antibodies called antiserum, which is usually commercially available; In a positive test, the bacteria agglutinate (or clump) when mixed with antibodies that were produced in response to the specific antigen; In a negative test, the bacteria are still evenly distributed in the saline and antiserum
• Coliforms

  Defined as all the aerobic and facultative anaerobic, nonspore-forming, gram-negative rods that are cytochrome-oxidase negative, capable of growth in the presence of bile salts, and ferment lactose at either 35 or 37 oC with the production of acid, gas and aldehyde within 24-48 hours (lactose fermenters)
• Coliforms

  • Escherichia
  • Klebsiella
  • Enterobacter
  • Citrobacter
• Fecal coliforms

  Ferment lactose at 44.5 oC, thus are also termed the thermotolerant coliforms; Refer to Escherichia coli
• Nonfecal coliforms


  Do NOT ferment lactose at 44.5 oC; Include species of Klebsiella, Enterobacter, and Citrobacter
• Noncoliforms

  • Proteus
  • Morganella
  • Providencia
  • Edwardsiella
  • Serratia
  • Hafnia
• Pathogenic enterics (true enteropathogens)

  • Salmonella
  • Shigella
  • Yersinia enterocolitica
  • Y. pseudotuberculosis
• The Enterobacteriaceae and related bacteria is a large, heterogeneous group of bacteria whose natural habitat is the intestinal tract of humans and animals
• Many members of this group are ubiquitous in nature — in soil, water, and vegetation
• The Enterobacteriaceae and related enterobacteria is the most frequently encountered bacterial isolates recovered from clinical specimens - both as normal flora and as agents of disease
• Similar to the K antigens, being outer to the O antigens, the H antigens may also interfere with the determination of O antigens
• Determination of O antigen

  Heat-labile H antigen must be inactivated by heat treatment first
• Pathogenic enterics (true enteropathogens)

  • Salmonella
  • Shigella
  • Yersinia enterocolitica
  • Y. pseudotuberculosis
• Pathogenic, non-enteric

  • Yersinia pestis
• Enterobacteriaceae and related bacteria

  • Large, heterogeneous group of bacteria whose natural habitat is the intestinal tract of humans and animals
  • Often commonly called the enteric bacteria or the enterobacteria
• This Enterobacteriaceae and related enterobacteria is the most frequently encountered bacterial isolates recovered from clinical specimens - both as normal flora and as agents of disease
• The diseases caused by these agents usually involve systems other than the gastrointestinal tract, such as the lungs and urinary tract
• Enterics

  • Pathogens within and outside the GIT
  • Pathogens within the GIT
  • Pathogens outside the GIT
• Pathogens within and outside the GIT

  • Escherichia coli
  • Salmonella species
  • Plesiomonas shigelloides
  • Yersinia enterocolitica
  • Yersinia pseudotuberculosis
• Pathogens within the GIT

  • Shigella species
• Pathogens outside the GIT

  • Klebsiella-Enterobacter-Serratia
  • Proteus-Morganella-Providencia
  • Citrobacter species
  • Edwardsiella tarda
• Non-enterics

  • Yersinia pestis
• Escherichia coli

  Colon bacillus
• Habitat and transmission of E. coli

  • Normal flora in the large intestine; may colonize the vagina and urethra
  • Acquired during birth and by fecal-oral route
• Urinary tract infection caused by E. coli

  • Commonly caused by E. coli, in approximately 90% of cases
  • Results from endogenous spread of the bacteria from the large intestine as resident flora, and mechanically introduced into the urethra
  • Occurs primarily in women, attributed to short urethra, proximity of urethra to anus, and colonization of vagina by fecal flora
• Signs and symptoms of E. coli UTI

  • Urinary frequency
  • Dysuria
  • Hematuria
  • Pyuria
  • Flank pain
• None of the symptoms or signs is specific for E coli infection
• Virulence factors of E. coli for UTI

  • P pili (P fimbriae) - primary virulence factor, allow attachment to urinary epithelial mucosa
  • Endotoxin - resides in cell wall, responsible for morbidity and mortality
  • Hemolysin - cytolysin that creates pores in eukaryotic cell membranes
  • Aerobactin - siderophore that enables E. coli to bind and transport iron
  • Capsular polysaccharide - antiphagocytic and inhibits opsonizing and lytic activities of complement
• E. coli as a cause of neonatal meningitis and septicemia

  • Acquired by newborns by vertical transmission from birth canal or contamination of amniotic fluid
  • Virulence factors: K1 antigen (capsular polysaccharide) - antiphagocytic, S fimbriae - bind to brain tissues, siderophore - allows chelation of iron
• E. coli is also an important cause of extraintestinal infections, mostly nosocomial, i.e., in hospitalized patients whose normal defense mechanisms have been breached
• Diarrheagenic E. coli pathotypes

  • Enterotoxigenic E. coli (ETEC)
  • Enteropathogenic E. coli (EPEC)
• Enterotoxigenic E. coli (ETEC)

  • Associated with weanling diarrhea and traveler's diarrhea
  • Causes watery, non-inflammatory diarrhea resembling cholera
  • Virulence factors: pili (fimbriae) - facilitate attachment, heat-labile toxin (LT) - activates adenylate cyclase, heat-stable toxin (ST) - stimulates guanylate cyclase