Food Microbiology 636 - Spring 2005

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• Food Microbiology 636 - Spring 2005
• j. gramp

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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

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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

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use fresh food sample of same type of food
TODAY
resuscitation of injured cells
selection for Salmonella
FRIDAY
MONDAY
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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

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Conventional Method
streak for isolation of presumptive Salmonella
colonies
further biochemical testing on typical Salmonella
colonies
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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

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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

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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

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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

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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

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Lab report

• disregard questions in lab book
• 4 questions from Salmonella
• contact me with any questions gramp.1_at_osu.edu