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