bacte

• Family Enterobacteriaceae


  • Largest heterogeneous collection of 27 genera and 7 enteric groups (also called as tribes)
  • Called enterics because they reside in gastrointestinal tract
  • Some found in normal microbiota
  • Feces composed of enteric bacteria

  
• Enterobacteriaceae


  • Gram negative bacilli or coccobacilli (plump bacilli)
  • Non-spore forming
  • Ferment glucose (anaerobic breakdown of carbohydrates and complex carbohydrates), with acid production
  • Aerobic → some are facultative anaerobe
  • Most are motile with peritrichous flagella
  • Non-motile: Shigella, Klebsiella, Yersinia (SKY)
  • Virulence factors: capsule, slime layer, or neither
  • Possess fimbriae (pilli)
  • Complex cell wall

  
• Monomers


  Smaller units from which larger molecules are made
• Polymers


  Molecules made from a large number of monomers joined together in a chain
• Synthetic polymers


  • nylon
  • polyethylene
  • polyester
  • Teflon
  • epoxy
• Enzymes


  • They increase the rate of chemical reactions without themselves being consumed or permanently altered by the reaction
  • They increase reaction rates without altering the chemical equilibrium between reactants and products
• As temperature increases


  The rate of reaction increases
• E. blattae: found in the intestine of cockroaches
• Members of the family Enterobacteriaceae

  • Opportunistic (take advantage of immunocompromised hosts)
  • Overt (obvious) pathogens
  • In between opportunistic and overt

  
• Opportunistic members

  Citrobacter spp., Enterobacter spp., Klebsiella spp., Proteus., Serratia

  
• Overt (obvious) pathogens

  Salmonella, Shigella spp., Yersinia spp.

  
• In between opportunistic and overt

  Escherichia coli
• Escherichia coli is part of normal microbiota and helpful in preventing harmful pathogens from growing in the GIT, however some strains like 0157:H7 are associated with food poisoning
• Pathogenic factors


  • Endotoxin (gram -)
  • KI antigen (from the capsule of E. coli)
  • Capsule of klebsiella pneumoniae
  • Vi antigen of salmonella typhi
  • Various surface antigen like fimbriae

  
• In the urinary tract, most frequently isolated are

  E. coli, P. mirabilis, K. pneumoniae
• Gram (-) pneumonia associated with

  Klebsiella pneumoniae
• Central Nervous System: Escherichia coli causes

  neonatal meningitis
• Lower respiratory tract: Most commonly, infections are caused by


  Klebsiella, Enterobacter spp., and Escherichia coli
• Blood stream (Sepsis): All members of Enterobacteriaceae


  The primary site of infection helps to determine the infecting organism

  
• Gastrointestinal Tract Infection

  • Salmonella spp
  • Shigella spp
  • Yersinia enterocolitica
  • Escherichia coli (Specific strains only)

  
• Urinary tract: All members of Enterobacteriaceae

  E. coli causes >80% of simple urinary tract infections
• Bacterial Species and Infections they commonly produce

  • Escherichia coli: Bacteriuria, septicemia, neonatal sepsis, meningitis, diarrheal syndrome
  • Shigella spp.: Diarrhea, dysentery
  • Edwardsiella spp.: Diarrhea, wound infection, septicemia, meningitis, enteric fever
  • Salmonella spp.: Septicemia, enteric fever, diarrhea
  • Citrobacter spp.: Opportunistic and hospital-acquired infections (wound, urinary)
  • Klebsiella spp.: Bacteriuria, pneumonia, septicemia
  • Enterobacter spp.: Opportunistic and hospital-acquired infection, wound infections, septicemia, bacteriuria
  • Serratia spp.: Opportunistic and hospital-acquired infection, wound infections, septicemia, bacteriuria
  • Proteus spp.: Bacteriuria, wound infection, septicemia
  • Providencia spp: Opportunistic and hospital-acquired infection, wound infections, septicemia, bacteriuria
  • Morganella spp.
  • Yersinia: Y. pestis (Plague), Y. pseudotuberculosis (Mesenteric adenitis, diarrhea), Y. enterocolitica (Mesenteric adenitis, diarrhea)
  • Erwinia spp.: Wounds contaminated with soil or vegetation
  • Pectobacterium spp.: Wounds contaminated with soil or vegetation

  
• Colony morphology

  • Gram negative coccobacilli or rods
  • Facultatively anaerobic → aerobic by nature
  • Macroscopic morphology broth: Large moist, gray colonies growth, some have mucoid colony due to presence of capsule

  
• MacConkey (MAC) agar


  • Selective (can inhibit growth of one organism while allowing the growth of other organisms) and differential (differentiate 2 characteristics of organism)
  • Inhibitory substance (Selective) → Bile salts and crystal violet (inhibits the growth of gram +)
  • Lactose fermentation (Differential) → Lactose (pink) vs non-lactose (white or colorless)
• Hektoen enteric (HE) agar

  • Selective and differential
  • Bile salts inhibit gram + and some gram – (Selective)
  • Lactose and sucrose fermentation (Differential) → Most nonpathogens ferment lactose and sucrose show orange color (low pH - ACIDIC), Pathogens (Salmonella and Shigella) green to blue-green color
  • Blue-green with black dot → Able to produce Hydrogen sulfide (H2S) production → Salmonella & Proteus
• Xylose lysine deoxychocolate (XLD) agar

  • Selective (not as selective as MAC and HE) and differential
  • Inhibitory substance (Selective) → Sodium deoxycholate (Inhibits gram + and some gram -)
  • Three carbohydrates sucrose and lactose in excess, and xylose with a phenol red (pH) indicator (Differential) → Acidic pH → Yellow → Fermentation took place, Alkaline pH → Red or Pink → No fermentation
  • Lysine present to detect lysine decarboxylation
  • Thiosulfate (indicator) present to detect H2S
  • Black spot → hydrogen sulfide (Salmonella)
• Lactose fermenters


  • Produce β-galactosidase
  • Ferment galactose to produce a simpler carbohydrate → lactose
  • Rapid LF - produce enzyme in high concentration, rapid manner
  • Slow/late lactose fermenter (SLF/LLF) - produce enzyme in low concentrations, slow manner
• Non-lactose fermenters


  Does not ferment lactose
• Triple Sugar Iron (TSI)


  • Has 3 sugars → Glucose, Lactose, Sucrose
  • Has Ferrous Ammonium Sulfate (NH4 SO4) → Hydrogen sulfide (H2S) indicator
  • TSI colors: Yellow → A, Red → K, Black → w H2S, Crack or space → gas production
  • A/A with gas: 3 sugars are fermented
  • K/A: only glucose is fermented
  • K/A with H2S
  • K/K: no sugar is fermented → isolated a non-fermenter
• Escherichia coli


  • Colon bacillus
  • Dry pink colonies on mac plates
  • Beta-hemolysis on BAP
  • Motile → Sex pili, fimbria
  • Possess O,H,K, antigen
  • Normal flora
  • Some strains are pathogenic

  
• Biochemical Reactions of Escherichia coli


  • Fermentation of glucose, lactose, trehalose, and xylose
  • Indole production from tryptophanase
  • Glucose fermentation via mixed acid pathway positive
  • Does not produce H2S, DNase, urease or Phenylalanine deamination (PAD)
  • Citrate negative
• IMVC result of Escherichia coli


  • Indole (+) – red ethereal layer
  • methyl red (+) – deep red color
  • Voges-Proskauer (-) – negative (yellow) | positive (red)
  • Citrate (-) – negative (green) | positive (prussian blue)

  
• Features of pathogenic E.coli


  • EPEC – causes non-bloody stool
  • EHEC – causes bloody stool, most common strain O157:H7
  • EIEC – causes mucoid bloody stool | dysentery (painful diarrhea) → may resemble shigella
  • ETEC – causes non-bloody stool
• Clinical types of E.coli


  • Enteropathogenic (EPEC) - Infantile diarrhea children <1 Year; nurseries and daycares
  • Enterotoxigenic (ETEC) - Diarrhea in infants and Adults in tropics and subtropics, Traveler's diarrhea
  • Enteroinvasive (EIEC) - Affects adults and children, Dysentery with direct penetration, invasion, and destruction of intestinal mucosa
  • Enterohemorrhagic (EHEC) - Hemorrhagic diarrhea, colitis, Hemolytic-uremic syndrome (HUS)
• E. coli O157:H7


  • Toxins produced: Verotoxin I (phage mediated cytotoxin), Verotoxin II
  • Can screen O157:H7 E. coli on SMAC plate (Sorbitol containing MacConkey plate) as it does not ferment sorbitol

  
• E. coli O157:H7


  Enterohemorrhagic (EHEC)
• E. coli O157:H7


  • Does not ferment lactose
  • Nonmotile
• E. coli O157:H7 causes hemorrhagic diarrhea, colitis
• E. coli O157:H7 can cause hemolytic-uremic syndrome (HUS)
• Hemolytic-uremic syndrome (HUS)


  • Low platelets, hemolytic anemia, kidney failure