Microbiology

• Gram negative rods


  • Oxidase negative
  • Oxidase Positive
• Oxidase negative


  • Enterobacteriaceae
  • Lactose-fermenters
  • Non-lactose fermenters
• Lactose-fermenters


  • Escherichia spp.
  • Klebsiella spp.
  • Enterobacter spp.
  • Citrobacter spp.
• Non-lactose fermenters


  • Salmonella spp.
  • Shigella spp.
  • Proteus spp.
  • Yersinia spp.
• Oxidase Positive


  • Pseudomonas
  • Vibrio
  • Campylobacter
  • Helicobacter
• Enterobacteriaceae


  • Found as normal flora in intestinal tract of humans and animals
  • Gram-negative, non-spore forming, aerobic and facultative anaerobic bacteria
  • Most are motile
  • Grow over a wide range of temperature in ordinary media
  • All ferment glucose with acid production
  • Oxidase negative
  • Release endotoxin from their cell wall
  • Some release exotoxin
  • Possess three types of antigens: H antigen (flagellar protein), K antigen (capsular polysaccharide or protein), O antigen (outer membrane lipopolysaccharide)
• Escherichia coli


  • Normal flora in human and animal gastrointestinal tract
  • Found in soil, water and vegetation
  • Most are motile; some are capsulated
• E.coli-associated diarrheal disease


  • Enteropathogenic E.coli (EPEC)
  • Enteroinvasive E.coli (EIEC)
  • Enterotoxigenic E.coli (ETEC)
  • Entero haemorrhagic E.coli (EHEC)
  • Enteroaggressive E.coli (EAEC)
• Enteropathogenic E.coli (EPEC)


  Causes outbreaks of self-limiting infantile diarrhea, also causes severe diarrhea in adults
• Enteroinvasive E.coli (EIEC)


  Non-motile, non-lactose fermenting E.coli invade the mucosa of the ileum and colon, and causes shigellosis-like dysentery in children in developing countries and travelers to these countries
• Enterotoxigenic E.coli (ETEC)


  Colonization factor of the organism promote adherence to epithelial cells of small intestine followed by release of enterotoxin which causes toxin-mediated watery diarrhea in infants and young adults, an important cause of traveler's diarrhea
• Entero haemorrhagic E.coli (EHEC)


  Cytotoxic verotoxin producing E.coli causes haemorrhagic colitis (severe form of diarrhea), and hemolytic uremic syndrome characterized by acute renal failure, hemolytic anemia and low platelet count
• Enteroaggressive E.coli (EAEC)


  Adhere to human intestinal mucosal cells and produce ST-like toxin and hemolysin, and causes acute and chronic diarrhea in persons in developing countries, also produce food-borne illness in developed countries
• E. coli resistance


  Commonly resistant to penicillin and ampicillin by production of b-lactamase enzymes, production of extended spectrum β-lactamases which inactivate many penicillins and cephalosporins is an increasing problem
• Antibiotics used to treat E. coli

  Cephalosporins, trimethoprim, ciprofloxacin and aminoglycosides
• Klebsiella


  • Non-motile, lactose-fermenting, capsulated, gram-negative rods
• Klebsiella species of medical importance

  • K. pneumoniae
  • K. rhinoscleromatis
  • K. ozenae
• K.pneumoniae


  Found as a commensal in the intestinal tract, and also found in moist environment in hospitals, an important nosocomial pathogen causing pneumonia, urinary tract infection, septicaemia and meningitis (especially in neonates), wound infection and peritonitis
• K. rhinoscleromatis


  Causes rhinoscleroma of nose and pharynx to extensive destruction of nasopharynx (hebra nose)
• K. ozaenae


  Causes ozena manifesting with foul smelling nasal discharge leading to chronic atrophic rhinitis
• Klebsiella resistance


  Often produce β-lactamases and are resistant to ampicillin, cephalosporins (e.g. cefotaxime), β -lactamase-inhibitor/penicillin combinations (e.g. co-amoxiclav) and aminoglycosides (e.g. gentamicin) can be used, but multiply resistant strains may limit antibiotic choice
• Enterobacter


  • Gram-negative lactose fermenting motile rods, found as a commensal in the intestinal tract of humans and animals and moist environments, closely related to Klebsiella spp.
• Enterobacter aerogens


  Associated with urinary tract infection, wound infection and septicemia in immunocompromised and chronically debilitated patients, hospital cross-infection with antibiotic-resistant strains is a particular problem
• Citrobacter


  • Gram-negative lactose fermenting motile rods, opportunistic pathogen
• Citrobacter freundii


  Associated with urinary tract infection, wound infection and septicaemia in immunocompromised and chronically debilitated patients
• Salmonella species of medical importance

  • S. typhi
  • S. paratyphi
  • S. choleraesuis
  • S. enteritidis
  • S. typhimurium
• Enteric fever


  Caused by S.typhi and S.paratyphi, transmitted by fecal-oral route via contaminated food and drinks, characterized by persistent fever, headache, malaise, chills, enlargement of liver and spleen, and skin rashes, paratyphoid fever is milder than typhoid fever, complications include intestinal perforation, lower gastrointestinal bleeding, dissemination to different body organs including meninges and brain, mortality rate is 10-15% for untreated cases and <1% for treated cases
• Bacteremia with focal lesions

  Caused by S. choleraesuis, manifests with blood stream invasion with focal lesions in lungs, bones and meninges, intestinal manifestation are often absent
• Gastroenteritis


  Caused by S. enteritidis and S. typhimurium, characterized by initial watery diarrhea, and later bloody mucoid diarrhea associated with crampy abdominal pain and tenesmus, bacteremia is rare (2-3 % of cases), usually resolves in 2-3 days
• Salmonella treatment


  For cases: Chloramphenicol, Fluoroquinolones, 3rd generation cephalosporins, for carriers: Ampicillin followed by cholecystectomy
• Salmonella prevention and control


  Sanity measures like hygienic food and drink handling, avoid carriers from food handling until properly treated, provision of injectable acetone-killed S. typhi suspensions vaccine or oral live, avirulent mutant strain of S. typhi vaccine in high endemic areas
• Shigella species of medical importance

  • S. dysenteriae
  • S. flexneri
  • S. boydii
  • S. sonnei
• Shigellosis (bacillary dysentery)


  Caused by S. flexneri and S. dysenteriae, transmitted by fecal-oral route, characterized by sudden onset of bloody mucoid diarrhea, abdominal cramp, tenesmus, fever, generalized muscle ache and weakness, complications include dehydration and electrolyte and acid-base disturbance, high prevalence in areas with poor sanitation, poor personal hygiene, and polluted water supply, young children are frequently affected
• Shigella treatment


  Ciprofloxacin, Cotrimaxazole, to suppress acute clinical attacks of dysentery and shorten the duration of symptoms
• Shigella prevention and control

  Sanitary control of water, food and milk, sewage disposal and fly control, antibiotic treatment of infected individuals
• Proteus


  • Found in the intestinal tract of humans and animals, soil, sewage and water, gram-negative, motile, non-capsulated, pleomorphic rods
• Proteus species of medical importance

  • P. mirabilis
  • P. vulgaris
• P. mirabilis


  Causes urinary tract infection, septicemia, abdominal and wound infection, secondary invader of ulcer, burn, pressure sores and chronic discharging ear
• P. vulgaris


  Important nosocomial pathogen, isolated in wound infection and urinary tract infection
• Yersinia


  • Animals are natural hosts, humans are accidental hosts, short, pleomorphic microaerophilic or facultatively anaerobic gram negative rods exhibiting bipolar staining with special stains