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The Gram-Negative Bacilli of Medical Importance 2/2

The Gram-Negative Bacilli of Medical Importance 2/2. Professor Sudheer Kher. Learning Objectives. Enlist medically important GNBs Explain the basis of classification of GNBs General properties of enterobacteriaceae Discuss the role of toxins and other virulence factors in pathogenesis

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The Gram-Negative Bacilli of Medical Importance 2/2

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  1. The Gram-Negative Bacilli of Medical Importance 2/2 Professor Sudheer Kher

  2. Learning Objectives • Enlist medically important GNBs • Explain the basis of classification of GNBs • General properties of enterobacteriaceae • Discuss the role of toxins and other virulence factors in pathogenesis • Describe the mechanism of action of various toxins6. • List pathogenicity Resources - Ananthnarayan

  3. Yersinia pestis • Nonenteric…tiny, gram-negative rod • virulence factors – *capsular & envelope proteins that protect against phagocytosis & foster intracellular growth *coagulase *endotoxin

  4. Yersinia pestis Yersia pestis in blood

  5. Yersinia pestis • humans develop plague through contact with wild animals (sylvatic plague) or domestic or semidomestic animals (urban plague) or infected humans • found in 200 species of mammals – rodents without causing disease • flea vectors – bacteria replicates in gut, coagulase causes blood clotting that blocks the esophagus; flea becomes ravenous

  6. Yersinia pestis Infection cycle

  7. Pathology of plague • 3-50 bacilli • bubonic – bacillus multiplies in flea bite, enters lymph, causes necrosis & swelling called a bubo in groin or axilla • septicemic – progression to massive bacterial growth; virulence factors cause intravascular coagulation & subcutaneous hemorrhage. Necrosis and skin blackening occur – black plague • pneumonic – infection localized to lungs, highly contagious; fatal without treatment • treatment: streptomycin, tetracycline or chloramphenicol • Killed or attenuated vaccine that gives a short-term protection exists

  8. Classic bubo (painful nodule that can rupture to the surface)

  9. Pasteruella multocida • zoonotic genus • opportunistic infections • animal bites or scratches cause local abscess that can spread to joints, bones, & lymph nodes (septicemia) • treatment: penicillin & tetracycline

  10. Hemophilus • tiny gram-negative pleomorphic rods • sensitive to drying, temperature extremes, & disinfectants • Fastidious. can’t grow on blood agar without special techniques. • some species are normal colonists of upper respiratory tract or vagina (H. aegyptius, H. parainfluenzae) • others are virulent species responsible of conjunctivitis, childhood meningitis, & chancroid

  11. Hemophilus • H. influenzae– acute bacterial meningitis, epiglottitis, otitis media, sinusitis, pneumonia, & bronchitis • meningitis symptoms: fever, vomiting stiff neck neurological impairment. High fatality is untreated • subunit vaccine Hib • H. aegyptius–conjunctivitis, pink eye • H. ducreyi– chancroid STD • H. parainfluenzae & H. aphrophilus– normal oral & nasopharyngeal flora; infective endocarditis

  12. Bacterial meningitis from H. influenzae

  13. Pinkeye (infectious conjunctivitis) H. aegyptius

  14. Serratia marcescens: common nosocomial pathogen in urinary and respiratory systems

  15. Bacteroides fragilis Strict intestinal anerobe Causes – Wound infections, UTI

  16. Vibrios Gram negative rods comma shaped facultative anaerobes oxidase positive simple nutritional requirements readily cultivated

  17. Occurrence -cholera third world 7 Pandemics so far. uncommon traveler ingestion of sea-food

  18. Transmission - V. cholerae feces • water • fresh • salt • food

  19. Cholera - attachment Gut lumen

  20. Cholera toxin- Choleragen B binds to gangliosides provides channel for A A catalyses ADP-ribosylation regulator complex activates adenylate cyclase

  21. Cholera -therapy • massive secretion of ions/water into • gut lumen • dehydration and death • therapy • fluid replacement • antibiotic therapy • vaccination • partially effective • not generally used • international travelers

  22. Vibrio parahemolyticus • raw sea-food • grows best in high salt • diarrhea

  23. CAMPYLOBACTER & HELICOBACTER • Gram negative rods • curved or spiral • genetically related

  24. Campylobacter jejuni pleomorphic

  25. Transmission infects the intestinal tract of animals chickens, cattle, sheep Transmitted milk meat products

  26. Campylobacter Gut lumen

  27. Isolation - Campylobacter microaerophilic grows best 42oC

  28. Campylobacter - symptoms • diarrhea • malaise • fever • abdominal pain • usually self-limiting • antibiotics occassionally • bacteremia • small minority

  29. stomach mucosa ulcers Helicobacter pylori Urease Important in neutralizing stomach acid

  30. Diagnosis -Helicobacter • Culture • - urease NH4+ CO2 • Direct detection of urease • CO2 derivedfrom labeled urea Therapy –HelicobacterAntibioticscures ulcers

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