Enterobacteriaceae

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Enterobacteriaceae

  1. 1. ENTEROBACTERIA & Pathogenic E. coli Prof. Abbas Hayat Gram negative bacteria which belong to the family Enterbacteriaceae. Also called coli forms.
  2. 2. MacConkey Medium :
  3. 3. Rapid presumptive identification of Gram negative bacteria. Lactose fermenters Pink colonies on Mac Conkeys media 1. Escherichia coli Metallic sheen on EMB, Motile No viscous colonies 2. Enterobacter species Raised colonies .Non viscous colonies 3. Klebseilla species Very viscous mucoid Non motile
  4. 4. Slow lactose fermenters on Mac Conkeys media 48 hours . •Citrobacter •Serratia •Providencia • Arizona. etc. ``opportunist pathogens``
  5. 5. Non Lactose fermenters Colorless colonies on Mac Conkeys • Shigella species: Non motile • Salmonella species: Motile • Proteus species: Swarming, urea hydrolyzed. • Pseudomonas species: Green pigment sweetish smell.
  6. 6. 1. Morphology and staining Gram negative rods , motile or non motile, peritrichous flagella, non sporing. 2. Culture: a. Mac Conkeys medium b. EMB (Eosin Methylene Blue agar) c. Blood agar d. CLED (Cystien Lactose Electrolyte Deficient Medium)
  7. 7. 3. Biochemical characteristics: • a. Lactose fermentation • b. Reduce nitrates to nitrites • c. Ferment glucose • d. Oxidase negative
  8. 8. • 1. Indole test: E. coli produces indole • 2. Methyl red: indicates pH of culture if below 4.5 positive. • 3. Voges –Proskere reaction: Depends on production of acetylmethylcarbinol from dextrose gives pink color positive in Enterobacter. • 4. Citrate test: Utilization of sodium citrate as sole source of carbon Klebseilla positive.
  9. 9. MNEMONIC FORMULA: • IMViC for E. coli is ++--, • Enterobacter is --++. Other tests: 1. Triple Sugar Iron or TSI medium 2. Urease production
  10. 10. • TRIPLE SUGAR IRON (TSI ) AGAR REACTION One such medium is TSI. • Medium contains 0.1 % glucose 1 % sucrose 1 % lactose ,Ferrous sulphate ( for detection of H2S, production ) and a pH indicator ( phenol red ). • Pored into test tube to produce a slant and a deep butt If only glucose is fermented , the slant and butt initially turn yellow from the small amount of acid produced ; as the fermented products are subsequently oxidized the slant turns Alkaline ( RED). • If lactose or sucrose is fermented so much acid is produced that slant and butt remain Acid (YELLOW).
  11. 11. TSI(Medium reactions) Escherichia coli - a facultative anaerobe, ferments both glucose and lactose as a carbon source, produce gas, but does not produce hydrogen sulfide
  12. 12. Salmonella enteritidis (serotype typhimurium) can ferment glucose but not lactose as carbon source and produces both hydrogen sulfide and gas.
  13. 13. Coliforms and Public Health: • Contamination of Public water by sewerage is detected by presence of E. coli Klebsiella and Enterobacter • Mainly E. coli is used as an indicator of unaccepted faecal contamination. Colony count > 4 dL.
  14. 14. Washing hands with sewerage water
  15. 15. End of Introduction to Enterobacteracaie. SMS sent by someone `` A perfect lecture should be like a girls skirt. Which iz long enough to cover the subject and short enough 2 create interest``
  16. 16. Should we continue with E. coli ?
  17. 17. Diseases Caused by E. COLI
  18. 18. • Habitat: E. coli is the head of the large bacterial family the Enterbacteriacae. Which consists of enteric bacteria, which are facultative anaerobic Gram-negative rods that live in the intestinal tracts of animals in health and disease.
  19. 19. Pathogenesis of E. coli Over 700 antigenic types or serotypes of E. coli have been recognized based on O, H, and K antigens. E. coli is responsible for three types of infections in humans: • 1. Urinary tract infections (UTI). • 2. Neonatal meningitis. • 3. Intestinal diseases (gastroenteritis) and Sepsis. These diseases depend on a specific array of pathogenic (virulence) determinants
  20. 20. Urinary tract infections • Uropathogenic E. coli causes 90% of the urinary tract infections (UTI) in anatomically-normal, unobstructed urinary tracts. • Bladder infections are 30-times more common in females of child bearing age than males by virtue of the shortened urethra.
  21. 21. • The typical patient with uncomplicated cystitis is a sexually-active first colonized in the intestine with an Uropathogenic E. coli strain. • Organisms propelled into the bladder from the peri urethral region during sexual intercourse. With the aid of specific adhesins they are able to colonize the bladder.
  22. 22. • Neonatal meningitis affects1/2,000-4,000 infants. Eighty percent of E. coli strains involved synthesize K-1 capsular antigens (K-1 is only present 20-40% of the time in intestinal isolates). • E. coli strains invade the blood stream of infants from the nasopharynx or GI tract and are carried to the meninges.
  23. 23. E. coli strains invade the blood stream of infants from the nasopharynx or GI tract and are carried to the meninges.
  24. 24. • E. coli strains invade blood stream of infants from the nasopharynx or GI tract and carried to the meningitis. • Epidemiologic studies show that pregnancy associated with increased rates of colonization by K-1 strains involved in the subsequent cases of meningitis in the newborn. GI tract is the portal of entry into the bloodstream. • Colonization is fairly common, invasion and the catastrophic sequelae are rare. • Neonatal meningitis requires antibiotic therapy that usually includes ampicillin and a third- generation cephalosporin
  25. 25. Gastrointestinal Disease
  26. 26. Intestinal diseases caused by E. coli As a pathogen, E. coli, of course, is best known for its ability to cause intestinal diseases. Five classes of E. coli that cause diarrhea are now recognized: • Enterotoxigenic E. coli (ETEC), • Enteroinvasive E. coli (EIEC), • Enterohemorrhagic E. coli (EHEC), • Enteropathogenic E. coli (EPEC), and • (EAggEC). Each class falls within a serological subgroup and manifests distinct features in pathogenesis.
  27. 27. • ETEC an imp. cause of diarrhea in infants and travelers in underdeveloped countries. • EIEC resemble Shigella in their pathogenic mechanisms and illness they produce. • EPEC induce watery diarrhea similar to ETEC. • The distinguishing feature of EAggEC strains is their ability to attach to tissue culture cells in an aggregative manner. These strains are associated with persistent diarrhea in young children. • EHEC causes a diarrheal syndrome, there is copious bloody discharge and no fever. Frequent life-threatening situation is its toxic effects on the kidneys (hemolytic uremia). EHEC has recently been recognized as a cause of serious disease (e.g. the Jack-in-the-Box outbreak in the Northwest).Pediatric diarrhea caused by this strain can be fatal due to acute kidney failure (hemolytic uremic syndrome [HUS]).
  28. 28. Treatment: • Depends on site of disease and resistance pattern. • Uncomplicated UTI 1-3 days with oral Trimethoprim- Sulfamethaxazole or an oral Penicillin, Amoxil /Ampicillin. • E. coli sepsis: Parental antibiotics e.g. Amino glycoside gentamicin or a cephalosporin. • Neonatal meningitis: Combination of ampicillin and gentamicin or a third or fourth generation cephalosporin. • E. coli diarrheal disease: Antibiotics usually not indicated. Timethoprim – Sulfamethaxazole may shorten duration. • Rehaydration more imp. Self limiting.
  29. 29. Lab Diagnosis: • Specimens: Stool, Urine, Blood, Pus, C.S.F. Food, and Water. • Culture: Blood agar and a differential medium like Mac Conkeys medium • Biochemical Tests; IMViC,. T.S.I reactions Citrate utilization, Sugar fermentations etc.
  30. 30. Prevention and Control. 1. No specific prevention No active or Passive Vaccination. 2. General measures: Removal of catheters, Prophylaxis with urinary antiseptics like Nitrofurantoin. 3. Caution regarding food and water.

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