Enterobacteriaceae

1. Enterobacteriaceae

2. Enterobacteriaceae • The most important bacterial family in human medicine • Well-defined diseases with typical clinical symptoms: • Typhoid fever, dysentery and plague • Nosocomial infections: • Urinary tract infections, pneumonias, wound infections and sepsis

3. Definition and significance • 41 genera with hundreds of species • Gram-negative, facultatively anaerobic rod • Natural habitat: intestinal tract of humans and animals

4. The Most Important Genera/Species/Vars of Enterobacteriaceae and the Corresponding Clinical Pictures

6. Virulence and pathogenicity • The most important pathogenicity factors: • Colonizing factors • Invasins • Endotoxin • Exotoxins • Enterobacteriaceae are the most significant contributors to intestinal infections

7. Identification of Enterobacteriaceae • Gram-negative rod • Usually motile (with few exceptions) • Facultative anaerobes • Grow on simple nutrient media • Oxidase test negative • Ferment glucose with acid or acid and gas

8. Sero-typing based on antigenic structure • O antigens: Somatic antigens (polysaccharide) • H antigens: Flagellar antigens (protein) • K antigens: Capsular antigens (carbohydrate) • e.g., serovar O18:K1:H7

9. Escherichia coli Klebsiella and Proteus

10. Escherichia coli

11. Escherichia coli on ChromID CPS agar

12. Natural habitat • Intestinal tract of humans and animals • indicator organism for fecal contamination of water and foods

13. Infections • Extraintestinalinfections • Intestinal infections (Diarrhoealdiseases)

14. Extraintestinal infections • Urinary tract infections • Wound infections • Peritonitis • Cholecystitis • Appendicitis • Sepsis and endotoxin induced shock • Neonatal meningitis

15. Diarrheagenicpathovars • EnteropathogenicE. coli (EPEC) • EnterotoxigenicE. coli (ETEC) • EnteroinvasiveE. coli (EIEC) • EnterohaemorrhagicE. Coli (EHEC) • EnteroaggressiveE. coli (EaggEC)

16. EPEC • Frequently cause diarrhea in infants • Vomiting, fever and prolonged diarrhoea • Infants mainly • Many serotypes

17. ETEC • Enterotoxins that cause watery diarrhoea similar to cholera • Infants and adults • Traveler diarrhea • Many serotypes

18. EIEC • Cause a dysentery like infection of the large intestine (similar to shigellosis) • Fever and colitis • Many serotypes

19. EHEC • Produce verocytotoxins and cause a hemorrhagic colitis (damage to vascular endothelia ) • Causes life-threatening haemorrhagicdiarrhoea • All ages

20. EHEC • No pus cells and no fever • It can progress to Haemolytic Uremic Syndrome → Renal failure • O157:H7 or verocytotoxin-producing E. coli • Contaminated meat products, unpasteurized milk and diary products

21. EaggEC • Chronic watery diarrhoea • Mainly in children

24. Klebsiella species

25. Klebsiella species

26. Klebsiellapneumoniae • Four subspecies: • K.p.pneumoniae • K.p. aerogenes • K.p. ozaenae • K.p. rinhoscleromatis

27. Infections caused by Klebsiellaspecies • UTI • Wound infections • Chest infections

28. Proteus species

29. Proteusspecies on Blood Agar

30. Medically important Proteus species • P. mirabilis • UTI • Wound infection • Septiceamia • Occasionally meningitis and chest infections • P. vulgaris • UTI and wound infections

31. Other enterobacteria

32. Other enterobacteria • Enterobacter • Citrobacter • Serratia • Opportunistic pathogens: • UTI • Wound infections • Septiceamia • Pulmonary infections

33. Laboratory diagnosis • Specimens: • Urine, pus, faeces, CSF, blood, sputum • Direct examination: • Gram –ve bacilli • Few capsulated • Culture aerobically at 36-37° C: • Blood agar • MacConkey agar • CLED • XLD and DCA

34. UTI • Midstream urine • Bacterial count • CFU/ml • ≥105/ml indicate an infection • 104/ml doubtful significance • ≤103/ml indicate a contamination

35. MacConkey agar showing lactose and non-lactose fermenting colonies

36. Escherichia coli (Gram negative)

37. Oxidase test