Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Lab Test > Raw Milk Bacteria > Flashcards

Raw Milk Bacteria Flashcards

1
Q

What is the maximum allowable Standard Plate Count (SPC) for Grade ‘A’ raw milk?

A

100,000 cfu/ml

SPC measures the overall bacterial quality of a sample.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the maximum allowable Somatic Cell Count (SCC) for Grade ‘A’ raw milk?

A

750,000 cells/ml

SCC is an indicator of milk quality and udder health.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

List three quality standards that raw milk must meet.

A
  • Free of drug residues
  • Free of added water
  • Free of sediment, contaminants, and other abnormalities

These standards are crucial for ensuring high-quality milk.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Why do dairy farmers seek to meet more stringent standards than regulatory requirements?

A

To receive substantial monetary premiums

Higher quality milk often commands better prices in the market.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What does the Standard Plate Count (SPC) measure?

A

The total number of aerobic bacteria present in milk

SPC is used extensively in regulatory and premium testing programs.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What other bacteriological tests are often performed in addition to SPC?

A
  • Preliminary Incubation Count (PIC)
  • Lab Pasteurization Count (LPC)
  • Coliform Bacteria Count

These tests help identify specific groups of bacteria associated with poor dairy practices.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

At what temperature and duration are milk samples incubated for SPC testing?

A

48 hours at 32°C (90°F)

This incubation encourages bacterial growth for accurate counting.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What does a high Standard Plate Count (SPC) indicate?

A

Contaminating bacteria are entering the milk

High SPC values suggest issues in milk production practices.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Fill in the blank: Aseptically collected milk from clean, healthy cows generally has SPC values of less than ______.

A

1,000

Low SPC values are a sign of good milking practices.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is one of the most frequent causes of high SPCs in raw milk?

A

Poor cleaning of the milking system

Residual milk on equipment provides nutrients for bacterial growth.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

True or False: Regulatory requirements alone ensure the highest quality of raw milk.

A

False

Many in the dairy industry advocate for more stringent standards beyond regulatory requirements.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What practices might contribute to increased bulk-tank SPCs?

A

Milking soiled cows, maintaining an unclean milking and housing environment, failing to rapidly cool the milk to or maintain it at less than 4.4°C (40°F)

Mastitic cows that shed infectious bacteria can also contribute to high SPCs.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What does the Preliminary Incubation Count (PIC) reflect?

A

Milk production practices

The PIC involves holding milk at 12.8°C (55°F) for 18 hours prior to plating.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How is the Preliminary Incubation Count (PIC) determined?

A

By comparing the bacterial counts of incubated milk with un-incubated milk using the SPC procedure

A significant increase is often considered 3-4 fold higher.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is generally considered a concerning PIC count?

A

> 50,000

This is regardless of the SPC.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What factors can lead to high Preliminary Incubation Counts (PICs)?

A

Failure to clean and sanitize the milking system, marginal cooling, prolonged storage times

Psychotrophic bacteria are often associated with high PICs.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the Lab Pasteurized Count (LPC)?

A

It estimates the number of bacteria that can survive the pasteurization process

LPC is determined by heating milk to 62.8°C (145°F) for 30 minutes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What are thermoduric bacteria?

A

Bacteria that survive the pasteurization heat treatment

LPCs are generally much lower than SPCs, with counts > 200-300 deemed high.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are common causes of high Lab Pasteurized Counts (LPCs)?

A

Chronic cleaning failures, significant levels of contamination from soiled cows, leaky pumps, old pipeline gaskets

Milkstone deposits can also contribute.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What does the Coliform Count procedure indicate?

A

It selects for bacteria associated with manure or environmental contamination

Coliforms may indicate fecal contamination but can also exist in the environment.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is a concerning Coliform Count?

A

> 50

Counts above this level indicate poor milking hygiene or other contamination sources.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

True or False: High coliform counts can only result from milking soiled cows.

A

False

They can also result from dirty equipment or environmental coliform mastitis.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Fill in the blank: The Preliminary Incubation Count (PIC) encourages the growth of bacteria that grow well at _______.

A

cool temperatures

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What are the suggested bacterial test standards for quality premiums?

A

Standards include Standard Plate Count, Laboratory Pasteurization Count, Preliminary Incubation Count, and Coliform Bacteria Count

Refer to Table 1 for specific values.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is the regulatory standard for Standard Plate Count?

A

< 200 - 300

No official standard set for Standard Plate Count.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is the suggested standard for Coliform Bacteria Count?

A

< 50

California regulatory standard is < 750.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What are the three main sources of microbial contamination in raw milk?

A
  • From within the udder
  • From the exterior of the udder
  • From milk handling and storage equipment

These sources influence the total bacteria count.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What factors influence microbial contamination of raw milk?

A
  • Health and hygiene of the cow
  • Environment of housing and milking
  • Cleaning and sanitizing procedures
  • Temperature and length of storage

These factors affect both total bacteria count (SPC) and types of bacteria present.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is the typical bacterial count in raw milk from healthy cows?

A

Less than 1000 total bacteria per ml

This count is considered low and typical for healthy cows.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

How does mastitis affect bacterial counts in bulk milk?

A

Cows with mastitis can shed in excess of 10^5 bacteria per ml

The total bulk tank count can significantly increase based on the infection status of cows.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Which mastitis organisms most influence the total bulk milk count?

A
  • Streptococcus agalactiae
  • Streptococcus uberis

Other pathogens may also influence the bulk count.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

True or False: The udder of healthy cows contributes significantly to the total bacteria count in bulk milk.

A

False

Healthy udders generally contribute very little to total bacteria count.

33
Q

Fill in the blank: The health and hygiene of the cow, the environment in which the cow is housed, and the procedures used in _______ are key factors influencing microbial contamination.

A

cleaning and sanitizing

Proper procedures are essential to minimize contamination.

34
Q

What is Staphylococcus aureus’s role in bulk tank counts?

A

Not thought to be a frequent contributor, though counts as high as 60,000/ml have been documented.

Reference: Gonzalez et al., 1986.

35
Q

Does the presence of implied pathogens in milk indicate they originated from cows with mastitis?

A

No, they can occur due to factors like dirty cows and poor equipment cleaning.

Potential environmental mastitis pathogens can also contribute.

36
Q

What does an increase in somatic cell count (SCC) indicate?

A

It can serve as supportive evidence that a mastitis bacterium may have caused an increase in milk.

Reference: Fenion et al., 1995.

37
Q

How are correlations between somatic cell responses and environmental mastitis organisms described?

A

Correlations are found to be poor.

Includes coliform bacteria, streptococci, and certain coagulase-negative Staphylococcus spp.

38
Q

What is significant about S. agalactiae and S. aureus in relation to milking equipment?

A

They are not thought to grow significantly on soiled milking equipment or under conditions of poor cooling.

39
Q

What does the presence of specific mastitis organisms in bulk tank milk indicate?

A

Considered strong evidence that they originated from infected cows.

References: Gonzalez et al., 1986; Bramley and McKinnon, 1990.

40
Q

Do mastitis organisms influence LPCs or PICs?

A

Generally, they do not influence LPCs or PICs, though coliform counts may be elevated in cases of coliform mastitis.

41
Q

What microorganisms can contribute to microbial contamination from the exterior of the udder?

A

Microorganisms associated with skin and those derived from the cow’s environment.

Includes manure, mud, feeds, or bedding.

42
Q

What is the impact of dirty cows on total bacteria counts?

A

Depends on the extent of soiling of the teat surface and wash procedures used before milking.

43
Q

How can teat soil significantly affect total bacteria count in milk?

A

If one gram of teat soil with 108 bacteria enters the milk, it can exceed 7,000 cfu/ml.

Based on a cow producing approximately 30 lb. (~13,400 gm) of milk.

44
Q

What is an effective method for reducing microorganisms in milk from soiled teats?

A

Thorough cleaning of the teat with a sanitizing solution followed by drying with a clean towel.

45
Q

What were the findings regarding coliform bacteria counts in untreated cows?

A

Coliform counts were relatively low, suggesting higher counts are likely due to other factors.

Factors include equipment and mastitis.

46
Q

What factor is thought to influence total bulk milk bacteria count significantly?

A

The degree of cleanliness of the milking system.

Reference: Olson and Mocquat, 1980.

47
Q

What can milk residues left on equipment contact surfaces do?

A

Support the growth of bacteria associated with contagious mastitis.

48
Q

What is a significant source of microorganisms in dairy farming?

A

Water used on the farm

Particularly psychotrophs that may contaminate soiled equipment and milk.

49
Q

What types of bacteria are often associated with environmental mastitis?

A

Coliforms

Certain strains can grow to significant numbers on milk contact surfaces.

50
Q

What environmental contaminants are more likely to grow on soiled equipment surfaces?

A

Bedding, manure, feeds

These contaminants can lead to increased microbial growth.

51
Q

What is the impact of old cracked rubber parts in dairy equipment?

A

Higher levels of thermoduric bacteria

These bacteria can persist despite cleaning efforts.

52
Q

What cleaning practices tend to select for faster-growing organisms?

A

Less efficient cleaning, lower temperatures, absence of sanitizers

This leads to higher PICs and elevated LPCs.

53
Q

Which sanitizers have been associated with reduced levels of psychotrophic bacteria?

A

Chlorine or iodine sanitizers

Effective use of these sanitizers minimizes bacterial growth.

54
Q

What is the significance of psychotrophic bacteria in milk?

A

Associated with high PICs and found in higher count milk

Often due to neglect of proper cleaning or sanitizing procedures.

55
Q

What effect does refrigeration storage have on milk?

A

Prevents growth of non-psychotrophic bacteria, selects for psychotrophic microorganisms

Contamination sources include soiled cows and dirty equipment.

56
Q

What happens to psychotrophic bacteria populations if raw milk is held too long before processing?

A

They increase in numbers

Particularly if held near the legal limit of 7.2°C (45°F).

57
Q

What is the result of holding milk at temperatures greater than 7.2°C (45°F)?

A

Rapid growth of bacteria other than psychotrophs

These bacteria can dominate raw milk.

58
Q

What type of bacteria are historically associated with poor cooling of milk?

A

Streptococci

They appear as pairs or chains of cocci on microscopic examination.

59
Q

What defect can certain strains of bacteria cause in milk?

A

A ‘malty defect’ with a distinct odor

This is associated with increased acidity in milk.

60
Q

At what storage temperature do contaminants tend to proliferate?

A

Greater than 15°C (60°F)

This temperature encourages growth of specific bacterial contaminants.

61
Q

Fill in the blank: Holding milk near _______ allows quicker growth of psychotrophic bacteria.

A

7.2°C (45°F)

This temperature threshold is critical for bacterial growth.

62
Q

True or False: All psychotrophic bacteria are thermoduric.

A

False

Most psychotrophic bacteria do not survive pasteurization.

63
Q

What is the effect of cooler temperatures of 1-2°C (34-36°F) on psychotrophic bacteria?

A

Delays the shift in microbial dominance

However, it does not prevent it indefinitely.

64
Q

What is microbial contamination of raw milk?

A

Contamination from a variety of microorganisms from different sources.

65
Q

What can high bacteria counts in raw milk result from?

A

A combination of factors such as dirty equipment and poor cooling.

66
Q

What does SPC stand for in the context of raw milk testing?

A

Standard Plate Count.

67
Q

What are some testing procedures used to evaluate the quality of raw milk?

A

LPC, PIC, coliform count.

68
Q

What do the LPC and PIC tests target?

A

Bacteria that are contaminants, not the natural flora of the cow.

69
Q

What is the purpose of bacterial culturing in the context of raw milk?

A

To identify mastitis bacteria.

70
Q

What is the significance of a SPC greater than 10,000?

A

Indicates possible contamination from dirty cows, dirty equipment, or poor cooling.

71
Q

True or False: High SPC counts are always due to mastitis.

A

False.

72
Q

Fill in the blank: High coliform counts in raw milk are _______.

A

Possible but not likely.

73
Q

What is the relationship between mastitis and bacterial counts in bulk tank milk?

A

High somatic cell counts can indicate mastitis bacteria presence.

74
Q

List some sources of microbial contamination as detected by bacteriological procedures.

A
  • Mastitis
  • Dirty cows
  • Dirty equipment
  • Poor cooling
75
Q

What does a high LPC count indicate?

A

Possible contamination.

76
Q

What is the potential source of contamination when SPC is high but PIC does not increase?

A

Possible contamination from other sources.

77
Q

Who authored the reference titled ‘Milk Under the Microscope’?

A

Atherton, H.V., and W.A. Dodge.

78
Q

What does a coliform count being high indicate?

A

Possible contamination but not likely from mastitis.

79
Q

Fill in the blank: The microbiology of raw milk is discussed in the book edited by _______.

A

R.K. Robinson.

Lab Test (13 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions