Salmonella

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Salmonella

  1. 1. Salmonellae <ul><li>Are often pathogenic for humans or animals when acquired by oral route </li></ul><ul><li>Transmitted from animals and animal products to humans, cause enteritis, systemic infection and enteric fever </li></ul><ul><li>Classification </li></ul><ul><li>Is complex, organisms are a continuum rather than a defined species </li></ul>
  2. 2. Salmonellae, cont. <ul><li>Family: enterobacteriaceae </li></ul><ul><li>On the basis of epidemiology, host range, biochemical reactions and structures of O, H, and Vi (when present) antigens  Kauffmann-White classification system </li></ul><ul><ul><li>E.g. Salmonella typhi, Salmonella typhimurium </li></ul></ul>
  3. 3. Salmonellae, cont. <ul><li>O Group Serotype Antig. Formula </li></ul><ul><li>D S. Typhi 9,12 (Vi):d:- </li></ul><ul><li>A S. paratyphi A 1,2, 12:1- </li></ul><ul><li>C 1 S. choleraesuis 6,7 :c:1,5 </li></ul><ul><li>B S. Typhimurium 1,4,5,12 :i:1,2 </li></ul><ul><li>D S. Enteritidis 1,9, 12 :g, m:- </li></ul><ul><li>O antigens: boldface numerals </li></ul><ul><li>(Vi): Vi antigen if present </li></ul><ul><li>Phase 1 H antigen: lower-case letter </li></ul><ul><li>Phase 2 antigen: numeral </li></ul>
  4. 4. Salmonellae, cont. <ul><li>Based on DNA-DNA hybridization studies </li></ul><ul><ul><li>7 evolutionary groups </li></ul></ul><ul><li>DNA hybridization Group I </li></ul><ul><ul><li>Nearly all salmonella serotypes that infect humans </li></ul></ul><ul><ul><ul><li>Salmonella enterica subspecies enterica </li></ul></ul></ul>
  5. 5. Salmonellae, cont.
  6. 6. Salmonellae, cont. <ul><li>Species name Salmonella enterica widely acceptable nomenclature </li></ul><ul><ul><li>Salmonella enterica subspecies enterica serotype Typhimurium  Salmonella Typhimurium </li></ul></ul><ul><li>Rare human infections with groups IIIa and IIIb </li></ul>
  7. 7. Salmonellae, cont. <ul><li>> 2500 serotypes of salmonellae </li></ul><ul><li>Including >1400 in DNA hybridization group I that can infect humans </li></ul><ul><li>4 serotypes that cause enteric fever identified in clinical laboratory by biochemical and serologic tests </li></ul>
  8. 8. Salmonellae, cont. <ul><li>Should be routinely identified because of clinical significance </li></ul><ul><ul><li>Salmonella Paratyphi A (serogroup A) </li></ul></ul><ul><ul><li>Salmonella Paratyphi B (serogroup B) </li></ul></ul><ul><ul><li>Salmonella Choleraesuis (serogroup C1) and </li></ul></ul><ul><ul><li>Salmonella Typhi (serogroup D) </li></ul></ul>
  9. 9. Salmonellae, cont. <ul><li>>1400 other salmonellae are serogrouped by O antigens as A, B, C 1 , C 2 , D, and E; some nontypeable </li></ul><ul><li>Isolates sent to reference laboratories for definitive serologic identification </li></ul>
  10. 10. Salmonellae, cont. <ul><li>Morphology and Identification </li></ul><ul><li>Vary in length </li></ul><ul><li>Most isolates are motile with peritrichous flagella </li></ul><ul><li>Grow readily on simple media </li></ul><ul><li>Almost never ferment lactose or sucrose </li></ul><ul><li>Form acid and sometimes gas from glucose and mannose </li></ul>
  11. 11. Salmonellae, cont. <ul><li>Usually produce H 2 S </li></ul><ul><li>Survive freezing in water for long periods </li></ul><ul><li>Resistant to brilliant green, sodium tetrathionate, sodium deoxycholate that inhibit other enteric bacteria </li></ul><ul><li>Useful for inclusion in media to isolate salmonellae from feces </li></ul>
  12. 12. Salmonellae, cont. <ul><li>Variation </li></ul><ul><li>May lose H antigens and become nonmotile </li></ul><ul><li>Loss of antigen is associated with a change from smooth to rough colony form </li></ul><ul><li>Vi antigen may be lost partially or completely </li></ul><ul><li>Antigens may be acquired or lost in the process of trunsduction </li></ul>
  13. 13. Salmonellae, cont. <ul><li>Pathogenesis and Clinical Findings </li></ul><ul><li>S. Typhi, S. Choleraesuis, S. Paratyphi A and S. Paratyphi B are primarily infective for humans </li></ul><ul><ul><li>Infection implies acquisition from a human source </li></ul></ul><ul><li>Vast majority chiefly pathogenic in animals that constitute reservoir for human infection </li></ul><ul><ul><li>Poultry, pigs, rodents, cattle, pets (turtles to parrots) </li></ul></ul>
  14. 14. Salmonellae, cont. <ul><li>Almost always enter via oral route usually with contaminated food or drink </li></ul><ul><li>Mean ID 10 5 – 10 8 salmonellae, perhaps as few as 10 3 </li></ul><ul><li>Host factors that contribute to resistance to infection </li></ul><ul><ul><li>Gastric acidity </li></ul></ul><ul><ul><li>Normal intestinal microbial flora and </li></ul></ul><ul><ul><li>Local intestinal immunity </li></ul></ul>
  15. 15. Salmonellae, cont. <ul><li>Produce 3 main types of disease in humans </li></ul><ul><ul><li>Enteric fever (typhoid fever) </li></ul></ul><ul><ul><li>Bacteremia with focal lesions and </li></ul></ul><ul><ul><li>enterocolitis </li></ul></ul>
  16. 16. Salmonellae, cont. <ul><li>Enteric Fevers Septicemias Enterocolitis </li></ul><ul><li>IP 7-20 days Variable 8-48 hrs </li></ul><ul><li>Onset Insidious Abrupt Abrupt </li></ul><ul><li>Fever Gradual, high Rapid rise, Usually low </li></ul><ul><li>plateau spiking septic T  </li></ul><ul><li>Durn Several wks Variable 2-5 days </li></ul><ul><li>of dis. </li></ul>
  17. 17. Salmonellae, cont. <ul><li>Enteric Fevers Septicemias Enterocolitis </li></ul><ul><li>GI sy. Early constipation, Often none Nausea, vomiting </li></ul><ul><li>bloody diarrhoea diarrhoea at onset </li></ul><ul><li>Blood +ve in 1 st to 2 nd +ve during Negative </li></ul><ul><li>Culture wk of dis. high fever </li></ul><ul><li>Stool -ve earlier dis.; Infrequently +ve soon after </li></ul><ul><li>Culture+ve 2 nd wk on +ve onset </li></ul>
  18. 18. Salmonellae, cont. <ul><li>Diagnostic Laboratory Tests </li></ul><ul><li>Specimens </li></ul><ul><li>Blood for culture must be taken repeatedly </li></ul><ul><ul><li>In enteric fevers and septicemia, blood cultures often +ve in 1 st wk of disease </li></ul></ul><ul><li>Bone marrow cultures may be useful </li></ul><ul><li>Urine cultures may be +ve after 2 nd wk </li></ul>
  19. 19. Salmonellae, cont. <ul><li>Stool specimens must be taken repeatedly </li></ul><ul><li>In enteric fevers, stools yield +ve results from 2 nd or 3 rd wk on </li></ul><ul><ul><li>In enterocolitis, during 1 st wk </li></ul></ul><ul><li>A +ve culture of duodenal drainage establishes presence of salmonellae in the biliary tract in carriers </li></ul>
  20. 20. Salmonellae, cont. <ul><li>Bacteriologic Methods for Isolation </li></ul><ul><li>Differential medium cultures </li></ul><ul><li>EMB, MacConkey’s or deoxycholate medium permits rapid detection of lactose non-fermenters </li></ul><ul><li>Gram +ve organisms are somewhat inhibited </li></ul>
  21. 21. Salmonellae, cont. <ul><li>Bismuth sulfite medium permits rapid detection of salmonellae </li></ul><ul><ul><li>form black colonies because of H 2 S production </li></ul></ul><ul><li>Many salmonellae produce H 2 S </li></ul><ul><li>Selective medium cultures </li></ul><ul><li>On SSA, Hektoen agar, XLD or DCA, favor growth of salmonellae and shigellae over other enterobacteriaceae </li></ul>
  22. 22. Salmonellae, cont.
  23. 23. Salmonellae, cont.
  24. 24. Salmonellae, cont. <ul><li>Enrichment cultures </li></ul><ul><li>On selenite F or tetrathionate broth, inhibit replication of normal intestinal bacteria </li></ul><ul><li>Permit multiplication of salmonellae </li></ul><ul><li>After incubation for 1-2 days, plated on differential and selective media </li></ul>
  25. 25. Salmonellae, cont.
  26. 26. Salmonellae, cont. <ul><li>Final identification </li></ul><ul><li>Suspect colonies from solid media identified by biochemical reaction patterns and slide agglutination tests with specific sera </li></ul>
  27. 27. Salmonellae, cont. <ul><li>Serologic Methods </li></ul><ul><li>Agglutination test </li></ul><ul><li>Known sera and unknown culture mixed on a slide </li></ul><ul><li>Clumping, when occurs, can be observed within a few minutes </li></ul><ul><li>Useful for rapid preliminary identification of cultures </li></ul>
  28. 28. Salmonellae, cont. <ul><li>Commercial kits available to agglutinate and serogroup salmonellae by their O antigens A, B, C 1 , C 2 , D and E </li></ul><ul><li>Tube dilution agglutination test (Widal test) </li></ul><ul><li>Serum agglutinins rise sharply during 2 nd and 3 rd wks of infection </li></ul>
  29. 29. Salmonellae, cont. <ul><li>At least 2 serum specimens at intervals 7-10 days needed to prove a rise in antibody titer </li></ul><ul><li>Serial (twofold) dilutions of unknown serum tested against antigens from representative salmonellae </li></ul>
  30. 30. Salmonellae, cont. <ul><li>Results interpreted as </li></ul><ul><ul><li>High or rising titer of O ( > 1:160) suggests that active infection is present </li></ul></ul><ul><ul><li>High titer of H ( > 1:160) suggests past immunization or past infection </li></ul></ul><ul><ul><li>High titer of Ab to Vi antigen occurs in some carriers </li></ul></ul>
  31. 31. Salmonellae, cont. <ul><li>Results must be interpreted cautiously </li></ul><ul><li>Possible presence of cross-reactive Ab limits use of serology in diagnosis of salmonella infection </li></ul><ul><li>Immunity </li></ul><ul><li>Infection of S Typhi or S Paratyphi usually confer a certain degree of immunity </li></ul>
  32. 32. Salmonellae, cont. <ul><li>Reinfection may occur but often milder than 1 st infection </li></ul><ul><li>Circulating Ab to O and Vi related to resistance to infection and disease </li></ul><ul><li>Relapses occur in 2-3 wks after recovery inspite of Ab </li></ul><ul><li>Secretory IgA Ab may prevent attachment to intestinal epithelium </li></ul>
  33. 33. Salmonellae, cont. <ul><li>Persons with S/S hemoglobin (sickle cell disease) are exceedingly susceptible to salmonella infections particularly osteomyelitis </li></ul><ul><li>Persons with A/S hemoglobin (sickle cell trait) may be more susceptible than normal individuals (those with A/A hemoglobin) </li></ul>
  34. 34. Salmonellae, cont. <ul><li>Treatment </li></ul><ul><li>Vast majority of enterocolitis do not require antimicrobial treatment </li></ul><ul><ul><li>Antimicrobial treatment of salmonella enteritis in neonates is important </li></ul></ul><ul><li>In enterocolitis, clinical symptoms and excretion of salmonellae may be prolonged by antimicrobial therapy </li></ul>
  35. 35. Salmonellae, cont. <ul><li>In severe diarrhoea replacement of fluids and electrolytes is essential </li></ul><ul><li>Invasive salmonella infections </li></ul><ul><ul><li>Ampicillin, trimethoprim-sulfamethoxazole or 3 rd generation cephalosporin </li></ul></ul><ul><li>Multiple drug resistance transmitted genetically by plasmids among enteric bacteria is a problem </li></ul>
  36. 36. Salmonellae, cont. <ul><li>Susceptibility testing is important adjunct to select a proper antibiotic </li></ul><ul><li>In most carriers, organisms persist in gall bladder (part. if gallstones are present) and biliary tract </li></ul><ul><li>Some chronic carriers cured by ampicillin alone </li></ul><ul><ul><li>Most cases cholecystectomy must be combined with drug treatment </li></ul></ul>
  37. 37. Salmonellae, cont. <ul><li>Epidemiology </li></ul><ul><li>Faeces of persons with unsuspected subclinical disease or are carriers are a more important source of contamination than frank clinical cases that are promptly isolated </li></ul><ul><ul><li>Carriers working as food handlers shedding organisms </li></ul></ul>
  38. 38. Salmonellae, cont. <ul><li>Many animals cattle, rodents, and fowl naturally infected with a variety of salmonellae </li></ul><ul><ul><li>Have bacteria in their meat, excreta or eggs </li></ul></ul><ul><li>High incidence in commercially prepared chickens widely publicized </li></ul>
  39. 39. Salmonellae, cont. <ul><li>Incidence of TF  but incidence of other salmonella infections  markedly in USA </li></ul><ul><ul><li>Aggravated by widespread use of animal feeds containing antimicrobial drugs that favor proliferation of drug-resistant salmonellae and potential transmission to humans </li></ul></ul>
  40. 40. Salmonellae <ul><li>Carriers </li></ul><ul><li>After manifest or subclinical infection, some individuals continue to harbor salmonellae in their tissues for variable length of time </li></ul><ul><li>Convalescent or healthy permanent carriers </li></ul>
  41. 41. Salmonellae, cont. <ul><li>3% of survivors of typhoid become permanent carriers </li></ul><ul><ul><li>Harboring organisms in gallbladder, biliary tract or rarely intestine or urinary tract </li></ul></ul><ul><li>Sources of Infection </li></ul><ul><li>Are food and drink contaminated with salmonellae </li></ul>
  42. 42. Salmonellae, cont. <ul><li>Following sources are important: </li></ul><ul><li>Water – contamination of feces often results in explosive epidemics </li></ul><ul><li>Milk and other diary products (ice cream, cheese, custard) </li></ul><ul><ul><li>Contamination with feces and inadequate pasteurization or improper handling </li></ul></ul><ul><ul><li>Some outbreaks traceable to source of supply </li></ul></ul>
  43. 43. Salmonellae, cont. <ul><li>Shellfish – from contaminated water </li></ul><ul><li>Dried or frozen eggs – from infected fowl or contaminated during processing </li></ul><ul><li>Meats and meat products </li></ul><ul><ul><li>From infected animals (poultry) or contamination with feces by rodents or humans </li></ul></ul>
  44. 44. Salmonellae, cont. <ul><li>Recreational drugs – Marijuana and other drugs </li></ul><ul><li>Animal dyes - Dyes such as carmine used in drugs, foods and cosmetics </li></ul><ul><li>Household pets – turtles, dogs, cats </li></ul><ul><li>Prevention and Control </li></ul><ul><li>Sanitary measures must be taken to prevent contamination of food and water by rodents or other animals that excrete salmonellae </li></ul>
  45. 45. Salmonellae, cont. <ul><li>Infected poultry, meats and eggs must be thoroughly cooked </li></ul><ul><li>Carriers must not be allowed to work as food handlers and should observe strict hygienic precautions </li></ul><ul><li>2 inj. of acetone-killed bacteria suspensions of S. Typhi followed by a booster inj. some months later </li></ul><ul><ul><li>Give partial resistance to small infectious inocula of typhoid bacilli but not to large ones </li></ul></ul>
  46. 46. Salmonellae, cont. <ul><li>Oral administration of a live avirulent mutant strain of S. Typhi  significant protection in high endemicity </li></ul><ul><li>Vaccines against others not recommended </li></ul>

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