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Salmonella

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Salmonella Powered By Docstoc
					Food Microbiology 636 - Spring 2005

              j. gramp
characteristics
•   Gram negative rod
•   Facultative anaerobe
•   Some serovars are pathogenic
•   Biochemical properties:
      •   glucose fermentation, acid and gas produced
      •   most do not ferment lactose or sucrose
      •   lysine and ornithine decarboxylation
      •   H2S production
Salmonellosis , the Disease
• Incubation:          12-36 hours
• Duration:            1-4 days
• Symptoms:            diarrhea, abdominal pain,
                       chills, moderate fever,
                       vomiting, dehydration,
                       headache
• Infectious dose:     as little as 1-10 cells

• Identification/detection more important than
  enumeration
use fresh
food        TODAY             resuscitation of injured cells
sample of
same type
of food                       selection for Salmonella
            FRIDAY



                     MONDAY
selective enrichment
• Selenite Cystine (SC) broth
  – selective agent: sodium acid selenite
  – Salmonella more resistant than most bacteria


• Tetrathionate (TT) broth
  – selective agent: tetrathionate
  – Salmonella have an enzyme to detoxify
Conventional Method


      streak for isolation of
      presumptive Salmonella
      colonies


      further biochemical
      testing on typical
      Salmonella colonies
isolation media
• BS – Bismuth Sulfite agar
     • selective: brilliant green (inhibits G+)
     • selective: bismuth (coliforms and G+)
     • differential: sulfite (desulfhydrase  H2S  reacts
                     with ferrous sulfate to form FeS black ppt)

     • Salmonella: black to green, with or w/o dark halo,
                   often w/ metallic sheen
isolation media cont.
• HE – Hektoen Enteric agar
     • selective: bile salts, bromothymol blue, acid fuchsin
                     (inhibits G+)
     • differential: pH indicators bromothymol blue, acid
                     fuchsin; detect acid production from
                     sugars (lactose, sucrose)  yellow
     • detection of desulfhydrase: ferric ammonium citrate
                     and sodium thiosulfate  black ppt

     • Salmonella: greenish blue w/ black center
isolation media cont.
• XLD – Xylose Lysine Desoxycholate
    • selective: desoxycholate (inhibits non-enterics)
    • differential: pH indicator phenol red detects acid
                    production from sugars (xylose, lactose,
                    sucrose)  yellow; decarboxylation of
                    lysine produces alkaline products 
                    reversion back to red
    • detection of desulfhydrase: ferric ammonium citrate
                    and sodium thiosulfate  black ppt

    • Salmonella: red w/ black centers
biochemical screening
• TSI – Triple Sugar Iron agar
     • glucose (0.1x), lactose, sucrose + protein
     • detection of desulfhydrase: sodium thiosulfate and
       ferrous sulfate  black ppt
     • Salmonella: red slant/yellow butt w/ black ppt K/A+
• LIA – Lysine Iron agar
     • glucose (sm amount), lysine, pH indicator
     • detection of desulfhydrase: ferric ammonium citrate
       and sodium thiosulfate  black ppt
     • Salmonella: purple slant/purple butt w/black ppt K/K+
Rapid method
• ELISA – Enzyme Linked Immunosorbent Assay
  – kits precoated with antibodies to Salmonella
    antigens
  – post-enrichment step – M broth (mannose)



  **Follow directions on website not lab book
Lab report
• disregard questions in lab book
• 4 questions from Salmonella

• contact me with any questions
  gramp.1@osu.edu

				
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posted:5/8/2013
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