MILK MICROBIOLOGY

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MILK MICROBIOLOGY          

• MILK MICROBIOLOGY

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Problems

• Does not reach as many people as water, but more
  of a hazard because
• milk comes from another living organism and
  naturally contains bacteria
• milk is a good growth medium
• milk is handled much more than water
• milk can contain antibiotic resistant organisms

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1. Humans to milk to humans

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• Milk is contaminated by human contact
• Used to be more of a problem before automation
• Tuberculosis, Cholera, Typhoid, Diptheria,
  Enteroviruses, others

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2. Cow to milk to humans

• On the cow the cow may have organisms on their
  skin or teat
• In the cow the cow is ill or carrying pathogens,
  may be symptomatic or asymptomatic

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Examples

• Mastitis infection in the mammary glands of the
  cow
• may be asymptomatic
• usually caused by Staphylococcus or
  Streptococcus
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• Brucellosis "Undulent Fever" caused by Brucella
  abortus
• cow can intermittently shed these organisms in
  their milk
• have been cases recently associated with raw
  milk
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• Campylobacter jejuni
• shed in the mammary gland, also found in feces
• has been a problem in raw milk since it is a
  low dose organism
• cows can be asymptomatic
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More Examples

• Salmonella
• mostly intestinal, but can get into milk
  (dairies have large amounts of feces around)
• cows can also be "intermittent mammary gland
  shedders" and be asymptomatic
• it is because of Salmonella dublin (low dose
  org.) that raw milk has a warning label
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• Listeria monocytogenes
• intestinal organism
• may survive pasteurization by protection of the
  white blood cells
• can grow at refrigeration temperatures
• high death rate
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• Yersinia entercolitica
• intestinal organism
• may grow at refrigeration temperatures
• has been found in chocolate milk even after
  passing current tests
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• Enterotoxigenic and Enteropathogenic E. coli OR
  E. coli 0157H7
• has been known to pass current tests

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Other

• Dairy cleanliness
• Improper pasteurization
• Raw milk
• Mishandling

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Tests for Pasteurization

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• Pasteurization kills all pathogens, not all
  bacteria

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1. Phosphatase Test

• Detects the presence of phosphatase enzyme, an
  enzyme found in milk that is destroyed by heat
• If phosphatase is found, then milk must not have
  been heated thoroughly
• Fast method, but unable to detect some
  contamination

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2. Total coliform test

• Similar to water testing only directly into
  brilliant green bile
• Grade A pasteurized milk may contain 10
  coliforms/ml (glass of milk approx. 300 ml)
• Certified Raw milk may contain only 1 coliform/ml

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3. Aerobic plate count (same as heterotrophic
plate count for water)

• does not detect pathogens but indicates
  mishandling or gross contamination
• Grade A pasteurized milk must contain lt
  30,000/ml
• before pasteurization Grade A must contain lt
  200,000/ml
• Certified Raw milk may contain only 10,000/ml

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4. Antibiotic Zonal Assay

• Look for residual antibiotics in milk,
  especially penicillin or other frequent
  sensitizers
• Similar to Kirby-Bauer method only use milk
  discs instead of antibiotic discs to see if
  inhibition occurs

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5. Direct microscopic analysis

• to look for gross contamination of bacteria or
  excessive white blood cells
• Psychrophiles and thermophiles
• to find organisms that may grow in refrigerator
  or survive pasteurization