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