Yersinia 2007


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Yersinia 2007

  1. 1. Yersinia <ul><li>Are short, pleomorphic gram negative rods that can exhibit bipolar staining </li></ul><ul><li>Are catalase positive, oxidase negative and microaerophilic or facultative anaerobic </li></ul><ul><li>Most have animals as their natural hosts, but they can produce serious human disease in humans </li></ul>
  2. 2. Yersinia <ul><li>The genus includes: </li></ul><ul><li>Yersinia pestis – plague </li></ul><ul><li>Yersinia pseudotuberculosis and Yersinia enterocolitica – human diarrhoeal diseases </li></ul>
  3. 3. Yersinia Pestis <ul><li>Gram negative rod with striking bipolar staining with special stains </li></ul><ul><li>Nonmotile </li></ul><ul><li>Grows as facultative anaerobe on many bacteriologic media </li></ul><ul><li>Growth is more rapid in media containing blood or tissue fluids and fastest at 30  C </li></ul>
  4. 4. Yersinia Pestis <ul><li>In cultures of blood agar at 37  C, colonies may be very small at 24 hours </li></ul><ul><li>A virulent inoculum, derived from infected tissue, produces gray and viscous colonies but after passage in the laboratory the colonies become irregular and rough </li></ul>
  5. 5. Yersinia Pestis <ul><li>Has little biochemical activity, is somewhat variable </li></ul><ul><li>Antigenic structure </li></ul><ul><li>All yersiniae possess lipopolysaccharides that have endotoxic activity when released </li></ul><ul><li>Produce many antigens and toxins that act as virulence factors </li></ul>
  6. 6. Yersinia Pestis <ul><li>The envelope contains a protein (fraction I) produced mainly at </li></ul><ul><li>37  C and confers antiphagocytic properties </li></ul><ul><li>Virulent, wild-type Y. pestis carries V-W antigens, which are encoded by genes on plasmids </li></ul><ul><li>A 72-kb plasmid is essential for virulence </li></ul>
  7. 7. Yersinia Pestis <ul><li>Avirulent strains lack the plasmid </li></ul><ul><li>Some stable avirulent strains have served as live vaccines </li></ul><ul><li>Produces coagulase at 28  C (normal temperature of the flea) but not at 35  C (transmission via fleas is low or absent in very hot weather) </li></ul>
  8. 8. Yersinia Pestis <ul><li>Among several exotoxins produced, one is lethal for mice in amounts of 1 µ g </li></ul><ul><li>This homogenous protein (MW 74,000) produces beta-adrenergic blockage and is cardiotoxic in animals </li></ul>
  9. 9. Yersinia Pestis <ul><li>Its role in human infection is unknown </li></ul><ul><li>Produces a bacteriocin (pesticin); the enzyme isocitrate lyase which is said to be distinctive and other products </li></ul><ul><li>Some antigens cross-react with other yersiniae </li></ul><ul><li>Bacteriophage may lyse other yersiniae </li></ul>
  10. 10. Yersinia Pestis <ul><li>Pathogenesis and Pathology </li></ul><ul><li>When a flea feeds on a rodent infected with Y. pestis , the ingested organisms multiply in the gut of the flea and helped by coagulase, block its proventriculus so that no food can pass through </li></ul>
  11. 11. Yersinia Pestis <ul><li>Subsequently the blocked and hungry flea bites ferociuosly and the aspirated blood contaminated with Y. pestis from the flea, is regurgitated into the bite wound </li></ul><ul><li>Inoculated organisms may be phagocytosed by polymorphonuclear cells and monocytes </li></ul>
  12. 12. Yersinia Pestis <ul><li>The organisms are killed by the polymorphonuclear cells but can multiply in the monocytes because bacteria are multiplying at 37  C, they produce antiphagocytic proteins and subsequently are able to resist phagocytosis </li></ul>
  13. 13. Yersinia Pestis <ul><li>The pathogens rapidly reach the lymphatics and an intense hemorrhagic inflammation develops in the enlarged lymph nodes, may undergo necrosis and become fluctuant </li></ul><ul><li>Often reach bloodstream and become widely disseminated </li></ul>
  14. 14. Yersinia Pestis <ul><li>Hemorrhagic and necrotic lesions may develop in all organs </li></ul><ul><li>Meningitis, pneumonia and serosanguineous pleuropericarditis are prominent features </li></ul><ul><li>Primary pneumonic plague results from inhalation of infective drops (from a coughing patient), with hemorrhagic consolidation, sepsis and death </li></ul>
  15. 15. Yersinia Pestis <ul><li>Clinical Findings </li></ul><ul><li>After an IP of 2 – 7 days, there is high fever and painful lymphadenopathy commonly with greatly enlarged, tender nodes (buboes) in the groin or axillae </li></ul><ul><li>Vomiting and diarrhoea may develop with early sepsis </li></ul>
  16. 16. Yersinia Pestis <ul><li>Later, DIC leads to hypotension, altered mental status, renal and cardiac failure </li></ul><ul><li>Terminally, signs of pneumonia and meningitis can appear </li></ul><ul><li>Y. pestis multiplies intravascularly and can be seen in blood smears </li></ul>
  17. 17. Yersinia Pestis <ul><li>Diagnostic Lab Tests </li></ul><ul><li>Plague should be suspected in febrile patients who have been exposed to rodents in known endemic areas </li></ul><ul><li>Rapid recognition and lab confirmation of disease are essential in order to institute lifesaving therapy </li></ul>
  18. 18. Yersinia Pestis <ul><li>Specimens </li></ul><ul><li>Blood for culture </li></ul><ul><li>Aspirates of enlarged lymph nodes for smear and culture </li></ul><ul><li>Acute and convalescent sera for antibody levels </li></ul><ul><li>Sputum for culture </li></ul><ul><li>CSF for smear and culture </li></ul>
  19. 19. Yersinia Pestis <ul><li>Smears </li></ul><ul><li>Examined after staining with Giemsa’s stain and with specific immunofluorescent stains </li></ul><ul><li>With Wayson’s stain, may show striking bipolar appearance </li></ul><ul><li>CSF and sputum smears should also be stained </li></ul>
  20. 20. Yersinia Pestis <ul><li>Culture </li></ul><ul><li>On BA, MCA plates and in infusion broth </li></ul><ul><li>Growth on solid media may be slow but blood culture are often +ve in 24 hrs </li></ul><ul><li>Tentatively identified by biochemical reactions </li></ul>
  21. 21. Yersinia Pestis <ul><li>Definite identification is best done by immunofluorescence </li></ul><ul><li>All cultures are highly infectious and must be handled with extreme caution </li></ul><ul><li>Serology </li></ul><ul><li>In previously unvaccinated, a convalescent serum antibody titre of 1:16 or greater is presumptive evidence of infection </li></ul><ul><li>A titre rise in two sequential specimens confirms the serologic diagnosis </li></ul>
  22. 22. Yersinia Pestis <ul><li>Treatment </li></ul><ul><li>Unless promptly treated, have a mortality rate of about 50%; pneumonic plague nearly 100% </li></ul><ul><li>Drug of choice is streptomycin </li></ul><ul><li>Tetracycline is an alternative drug and is sometimes given in combination with streptomycin </li></ul><ul><li>Drug resistance has not been reported </li></ul>
  23. 23. Yersinia Pestis <ul><li>Epidemiology and Control </li></ul><ul><li>Plague is an infection of wild rodents (field mice, gerbils, moles, skunks, and other animals) that occurs in many parts of the world </li></ul><ul><li>Chief enzootic areas are India, Southeast Asia (Vietnam), Africa, North and South America </li></ul>
  24. 24. Yersinia Pestis <ul><li>The Western states of US and mexico alway contain reservoirs of infection </li></ul><ul><li>Epizootics with high mortality rates occur intermitently; at such times, the infection can spread to domestic rodents (rats) and other animals (cats) and humans can be infected by flea bites or by contact </li></ul>
  25. 25. Yersinia Pestis <ul><li>The commonest vector is the rat flea Xenopsylla cheopis but other fleas may also transmit the infection </li></ul><ul><li>Control requires surveys of infected animals, vectors and human contacts </li></ul><ul><li>All patients with suspected plague should be isolated particularly if pulmonary involvement has not been ruled out </li></ul>
  26. 26. Yersinia Pestis <ul><li>All specimens must be treated with extreme caution </li></ul><ul><li>Contacts of patients with suspected plague pneumonia should receive tetracycline as chemoprophylaxis </li></ul><ul><li>A formalin-killed vaccine is available for travelers to hyperendemic areas and for persons at special high risk </li></ul>
  27. 27. Yersinia enterocolitica and Y. pseudotuberculosis <ul><li>Non-lactose fermenting gram negative rods that are urease-positive and oxidase negative </li></ul><ul><li>Grow best at 25  C and are motile at </li></ul><ul><li>25  C but nonmotile at 37  C </li></ul><ul><li>Found in intestinal tract of a variety of animals in which they cause disease </li></ul>
  28. 28. Yersinia enterocolitica and Y. pseudotuberculosis <ul><li>and are transmissible to humans in whom they can produce a variety of clinical syndromes </li></ul><ul><li>Y. enterocolitica exists in >50 serotypes </li></ul><ul><li>Most isolates from human disease belong to serotypes O3, O8 and O9 </li></ul>
  29. 29. Yersinia enterocolitica and Y. pseudotuberculosis <ul><li>There are striking geographic differences in the distribution of Y. enterocolitica serotypes </li></ul><ul><li>Y. pseudotuberculosis exists in at least six serotypes, but serotypes O1 accounts for most human infections </li></ul>
  30. 30. Yersinia enterocolitica and Y. pseudotuberculosis <ul><li>Y. enterocolitica can produce a heat-stable enterotoxin but the role of toxin in diarrhoea associated infection is not well defined </li></ul><ul><li>Y. enterocolitica has been isolated from rodents and domestic animals and water contaminated by them </li></ul>
  31. 31. Yersinia enterocolitica and Y. pseudotuberculosis <ul><li>Transmission to humans occurs by contamination of food, drink or fomites </li></ul><ul><li>Y. pseudotuberculosis occurs in domestic and farm animals and birds which excrete the organisms in feces </li></ul><ul><li>Human infection probably results from ingestion of materials contaminated with animal feces </li></ul><ul><li>Person to person transmission with either of these organisms is probably rare </li></ul>
  32. 32. Yersinia enterocolitica and Y. pseudotuberculosis <ul><li>Pathogenesis and Clinical Findings </li></ul><ul><li>An inoculum of 10 8 – 10 9 yersiniae must enter the alimentary tract to produce infection </li></ul><ul><li>During IP of 5 – 10 days, yersiniae multiply in the gut mucosa particularly the ileum </li></ul>
  33. 33. Yersinia enterocolitica and Y. pseudotuberculosis <ul><li>Leads to inflammation and ulceration and leukocytes appear in feces </li></ul><ul><li>The process may extend to mesenteric lymph nodes and rarely to bacteremia </li></ul><ul><li>Early symptoms include fever, abdominal pain, and diarrhoea </li></ul><ul><li>Diarrhoea ranges from watery to bloody and may be due to an enterotoxin or to invasion of the mucosa </li></ul>
  34. 34. Yersinia enterocolitica and Y. pseudotuberculosis <ul><li>At times abdominal pain is severe and located in the right lower quadrant suggesting appendicitis </li></ul><ul><li>1 to 2 weeks after onset some pts develop arthalgia, arthritis and erythema nodosum suggesting immunologic reaction to the infection </li></ul><ul><li>Very rarely, it produces pneumonia, meningitis or sepsis; in most cases, it is self-limited </li></ul>
  35. 35. Yersinia enterocolitica and Y. pseudotuberculosis <ul><li>Diagnostic Lab Tests </li></ul><ul><li>Specimens </li></ul><ul><li>Stool, blood, or material obtained at surgical exploration </li></ul><ul><li>Culture </li></ul><ul><li>No. in stool may be small and can be increased by cold enrichment </li></ul>
  36. 36. Yersinia enterocolitica and Y. pseudotuberculosis <ul><li>A small amount of feces or a rectal swab is placed in buffered saline, pH 7.6, and kept at 4  C for 2-4 weeks; many fecal organisms do not survive but Y. enterocolitica will multiply </li></ul><ul><li>Subcultures made at intervals on MCA may yield yersiniae </li></ul>
  37. 37. Yersinia enterocolitica and Y. pseudotuberculosis <ul><li>Serology </li></ul><ul><li>In paired serum specimens taken 2 or more weeks apart, a rise in agglutinating antibodies can be shown </li></ul><ul><li>However, cross reactions between yersiniae and other organisms such as vibrios, salmonellae, brucellae may confuse the results </li></ul>
  38. 38. Yersinia enterocolitica and Y. pseudotuberculosis <ul><li>Treatment </li></ul><ul><li>Most yersinia infections with diarrhoea are self-limited </li></ul><ul><li>Y. enterocolitica is generally susceptible to aminoglycosides, chloramphenicol, tetracycline, trimethoprim-sulphamethoxazole,piperacillin, 3 rd generation cephalosporins and fluoroquinolones </li></ul>
  39. 39. Yersinia enterocolitica and Y. pseudotuberculosis <ul><li>Typically resistant to ampicillin and 1 st generation cephalosporins </li></ul><ul><li>Proved yersinia sepsis or meningitis has a high mortality rate but deaths occur mainly in immunocompromised patients </li></ul><ul><li>Yersinia sepsis can be successfully treated with 3 rd generation cephalosporins possibly in combination with aminoglycosides or a fluoroquinolone possibly with another antimicrobial </li></ul>
  40. 40. Yersinia enterocolitica and Y. pseudotuberculosis <ul><li>Prevention and Control </li></ul><ul><li>Contact with farm and domestic animals, their feces or materials contaminated by them probably accounts for most human infections </li></ul><ul><li>Meat and dairy products have occasionally been indicated as sources of infection, and group outbreaks have been traced to contaminated food or drink </li></ul><ul><li>Conventional sanitary precautions are probably helpful </li></ul>
  41. 41. Pasteurella <ul><li>Species are primarily animal pathogens but can produce a range of human diseases </li></ul><ul><li>Pasteurella formerly included all yersiniae and francisellae </li></ul><ul><li>Are nonmotile gram negative coccobacilli with a bipolar appearance on stained smears </li></ul>
  42. 42. Pasteurella <ul><li>Are aerobes or facultative anaerobes that grow readily on ordinary bacteriologic media at 37  C </li></ul><ul><li>Are all oxidase positive and catalase positive but diverge in other biochemical reactions </li></ul><ul><li>P. multocida occurs worldwide in the respiratory and GI tracts of many domestic and wild animals </li></ul>
  43. 43. Pasteurella <ul><li>Perhaps most common organism in human wounds inflicted by bites from cats and dogs </li></ul><ul><li>One of the common causes of hemorrhagic septicaemia in a variety of animals including rabbits, rats, horses, sheep, fowl, cats and swine </li></ul><ul><li>Can also produce human infections in many systems and may at times be part of normal human flora </li></ul>
  44. 44. Pasteurella <ul><li>P. haemolytica occurs in the URT of cattle, sheep, swine, horses and fowl </li></ul><ul><li>Prominent cause of epizootic pneumonia in cattle and sheep and of fowl cholera in chickens and turkeys causing major economic losses </li></ul><ul><li>Human infection appears to be rare </li></ul>
  45. 45. Pasteurella <ul><li>P. pneumotropica is a normal inhabitant of the RT and gut of mice and rats </li></ul><ul><li>Can cause pneumonia or sepsis when the host-parasite balance is disturbed </li></ul><ul><li>A few human infections have followed animal bites </li></ul><ul><li>P. ureae has rarely been found in animals but occurs as part of a mixed flora in human chronic respiratory disease or other suppurative infections </li></ul>
  46. 46. Pasteurella <ul><li>Most common presentation is a history of animal bite followed within hrs by an acute onset of redness, swelling and pain </li></ul><ul><li>Regional lymphadenopathy is variable and fever is often low grade </li></ul><ul><li>Infections sometimes present as bacteremia or chronic respiratory infection without an evident connection with animals </li></ul>
  47. 47. Pasteurella <ul><li>P. multocida is susceptible to most antibiotics </li></ul><ul><li>Pen G is considered the drug of choice for P. multocida infections resulting from animal bites </li></ul><ul><li>Tetracycline and fluoroquinolones are alternative drugs </li></ul>