How do microorganisms get into milk

1
How do microorganisms get into milk ?

• Bhushan Jayarao
• Department of Veterinary Science
• Pennsylvania State University

2
CONTAMINATION OF RAW MILK ON THE FARM

• Udder
• Exterior of the teats and udder
• Milker
• Aerial contamination
• Milking equipment bulk tank

3
Udder-1

• Healthy udder - 0 to lt 100 bact./ ml
• Mastitis
• Subclinical mastitis - lt 10,000 bact./ ml
• Clinical mastitis quarters - gt 10,000,000
  bact./ ml
• Streptococcus agalactiae
• Staphylococcus aureus

4
Udder-2

• Mastitis organisms can increase the bulk tank
  count by 100,000 organisms/ ml.
  
  
  
  
  
• Usually observed with Streptococcal and Coliform
  mastitis.

5
Udder-3

• Most mastitis organisms grow at body temperature
  (37 C)
  
  
  
  
• Many mastitis organisms grow very slowly in bulk
  tank milk (5 C). THEY ARE STILL ALIVE.
  
  
  
  
  
• ON PASTEURIZATION MOST OF THE MASTITIC PATHOGENS
  ARE KILLED

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Udder-4

• mastitis organisms are usually put into two
  groups
• Contagious
• Staph. aureus
• Strep. agalactiae
• Environmental
• Coliforms
• Strep. dysgalactiae
• Strep. uberis

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Udder -4

• CONSUMPTION OF RAW MILK
  
  
  
  
  
• MYCOBACTERIUM TUBERCULOSIS
• BRUCELLA ABORTUS
• STREPTOCOCCUS AGALACTIAE
• S. AUREUS
• LISTERIA MONOCYTOGENES
• SALMONELLA

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EXTERIOR OF UDDERS AND TEATS-1

• Feces/ Manure
• Soil
• Bedding
• Feed

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EXTERIOR OF UDDER AND TEATS-2

• Between milkings, cows teats may become soiled
  with dung, mud, bedding materials.
  
  
  
  
  
• If not removed, microorganisms present in the
  dirt, are washed into the milk.

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EXTERIOR OF UDDER AND TEATS-3

• Milk from cows with unwashed teats and heavily
  soiled dung may have a bacterial counts gt 100,000
  bact. /ml

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EXTERIOR OF UDDER AND TEATS-4

• Clipping cows around the flanks and udders
  reduces amount of
  contamination.
  
  
  
  
  
• Average bacteria/ml raw milk
• _____________________________________________
• Farm of cows not clipped
  clipped
• _____________________________________________
• A 80 20,000 5,000
• B 45 48,000 10,000
• C 35 200,000 80,000
• D 20 350,000 200,000
• ______________________________________________

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EXTERIOR OF UDDER AND TEATS-5

• Wash the udder with warm sanitizer solution.
• Iodophors commonly used.
• Udder is dried with single use paper towel.
• Average bacteria/ml raw milk
• _________________________________________
• Farm of cows Not washed washed
• _________________________________________
• A 80 20,000 6,800
• B 45 48,000 20,000
• C 35 200,000 100,000
• D 20 350,000 230,000
• _________________________________________

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EXTERIOR OF UDDER AND TEATS-6
Level of bacteria in bedding materials. __________
____________________________________
Bacillus Bedding Total Count Coliforms
spores ___________________________________________
___ Straw 108 105
105 Wood Shavings 1010 105 106
Sand 109 105 106
______________________________________________
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EXTERIOR OF UDDERS AND TEATS -7
Types of organisms on udders and teats.

1. Micrococci. 2. Coagulase-negative
staphylococci. 3. Fecal enterococci. 4. Coliforms.
5. Bacillus spores 1) B. lichenformis 2) B.
subtilis 3) B. cereus 4) B. pumilus 6. Clostridi
um spp. from silage. 1) Cl. sporogenes 2) Cl.
tyrobutyricum
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Aerial contamination

• Least important source of bacteria in milk
• Few bacteria carried into milk by air entering
  the milking machine.
• Cowsheds/ parlors do not exceed 200 bacteria /
  litre of air.
• Organisms in parlor air
  1) Micrococci, 2) Coryneforms,
  3) Bacillus spores.
• Few numbers of Streptococci and Gram-negative
  bacteria also observed.

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Milker

• Risk of contamination from the milker are
  much less with machine milking.
  
  
  
  
  
• Milkers with infectious diseases contaminating
  the milk is not ruled out.

17
Water supply

• Many farms rely on untreated water supplies.
• The number and types of bacteria in untreated
  waters vary considerably
• Organisms could originate from
• feces
• soil or vegetation

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Water supply -2

• fecal origin
• coliforms
• fecal streptococci
• clostridia
• Soil or vegetation
• Pseudomonas
• Coliforms
• Bacillus spores

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Water supply -3

• Washing equipment with untreated water may not
  significantly increase bacterial numbers in raw
  milk.
  
  
  
  HOWEVER
• Multiplication of bacteria in residual water in
  the equipment will result in more serious
  contamination and problems.
  
  
  
  
  ALSO
• Lead to establishment and development of some
  undesirable types such as gram-negative
  psychrotrophic bacteria.

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Milking equipment-1

• Major source of contamination is unsanitized
• or poorly sanitized milk contact surfaces.
• Complexity of milking machines and some of
  
  
  
  
  their components, cleaning
  disinfection may
  
  
  
  not be fully effective
• Milk residues are not completely removed from
  
  
  
  
  the equipment and tend to accumulate
  daily.
  
  
  
  
• Bacterial numbers increase rapidly between
  
  
  
  
  milkings

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Milking equipment -2

• Growth of contaminating bacteria possible if
  temperature control not maintained.
  
  
  
  
  
• Milk should be cooled to lt40 F within 2 hours and
  not warmed above 50 F when next milking's milk
  is added.

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Milking equipment-3

• Milking equipment is seldom uniformly
  contaminated
  
  
  
  
  
• The bacteria and milk residues accumulate in
  difficult-to-clean areas
  
  
  
  
  
• CIP systems give rinse counts of lt 5 x 104
  bacteria /feet of equipment

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Milking equipment-4

• Bulk tanks are more easily cleaned than milking
  machines.
  
  
  
  
  
• Agitator, dipstick, plug or outlet cock, could
  cause problems.
  
  
  
  
  
• Mechanical cleaning more effective than manual
  cleaning.

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Milking equipment-5
Increase in bacteria/ml in "clean" milk over a
12-h period. Storage Temp. Increase 40 F
None 50 F 5X 60 F 15X 70 F
700X 80 F 3,000X
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Milking equipment-6

• If milking machines alone are responsible for
  counts
• gt 5.0 x 104, cleaning sanitation must be
  seriously
• deficient.
• ______________________________________________
• of distribution of counts/m2
• Equipment tests gt105 gt106 gt107 gt108
  gt109
• __________________________________________________
  ____
• Milking Machines 702 98.3 91.0 66.7
  26.1 7.4
• Hand brushed tank 284 77.7 56.2 26.5
  4.9 1.1
• Auto. Sprayed tank 194 56.0 33.7 14.0
  2.6 0.0
• Tank outlet plug 755 82.5 67.9 46.7
  23.8 8.9
• __________________________________________________
  ____

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Milking equipment -7

• Mastitis pathogens do not form a part of the
  microflora of milking equipment.
  
  
  
  
  
• Application of very hot detergent-disinfectant
  solutions allow selection of Micrococci,
  Streptococci and Bacillus.
  
  
  
  
  
• Use of lower temp. (40-50 C) allow several
  different kinds of bacteria to survive.

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Milking equipment -8

• The microflora is relatively restricted with one
  particular group or two.
  
  
  
  
  
• The groups are
• Micrococci, Streptococci, Gram-negative rods,
  and asporogenous gram positive rods
  
  
  
  
  
• In any one milking machine, the microflora can be
  consistent or vary from time to time.

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Milking equipment -9

• Organisms that grow at refrigeration
  tempereatures are of concern in the Bulk tank
  
  
  
  
  
  
• These organisms are mainly
• gram-negative rods e.g. Pseudomonas
• gram positive rods e.g. Bacillus

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Processing plant

• Pseudomonas and Bacillus spp. are frequently
  isolated from bulk tank milk.
  
  
  
  
  
• When milk is received at the processing plant (in
  Netherlands) it is thermised.
• heated to 63 C for 15 s on arrival and then
  cooled immediately to 5-6 C.

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Putting it all together
__________________________________________________
_____ Milk Production
Storage SPC/ml
Conditions Temp. Fresh 24
hours 48 hours _______________________________
________________________ 1. Clean cows
40 F 4,300 4,100
4,600 environment, 50 F 4,300
14,000 130,000 and utensils 60 F
4,300 1,600,000 33,000,000 2. Clean
cows, 40 F 39,000 88,000
120,000 dirty environment, 50 F 39,000
180,000 830,000 and utensils 60
F 39,000 4,500,000 99,000,000 3. Dirty
cows, 40 F 140,000 280,000
540,000 environment, 50 F 140,000
1,200,000 14,000,000 and utensils
60 F 140,000 25,000,000 640,000,000 _________
_______________________________________________