Raw Milk Bacteria Flashcards
What is the maximum allowable Standard Plate Count (SPC) for Grade ‘A’ raw milk?
100,000 cfu/ml
SPC measures the overall bacterial quality of a sample.
What is the maximum allowable Somatic Cell Count (SCC) for Grade ‘A’ raw milk?
750,000 cells/ml
SCC is an indicator of milk quality and udder health.
List three quality standards that raw milk must meet.
- Free of drug residues
- Free of added water
- Free of sediment, contaminants, and other abnormalities
These standards are crucial for ensuring high-quality milk.
Why do dairy farmers seek to meet more stringent standards than regulatory requirements?
To receive substantial monetary premiums
Higher quality milk often commands better prices in the market.
What does the Standard Plate Count (SPC) measure?
The total number of aerobic bacteria present in milk
SPC is used extensively in regulatory and premium testing programs.
What other bacteriological tests are often performed in addition to SPC?
- Preliminary Incubation Count (PIC)
- Lab Pasteurization Count (LPC)
- Coliform Bacteria Count
These tests help identify specific groups of bacteria associated with poor dairy practices.
At what temperature and duration are milk samples incubated for SPC testing?
48 hours at 32°C (90°F)
This incubation encourages bacterial growth for accurate counting.
What does a high Standard Plate Count (SPC) indicate?
Contaminating bacteria are entering the milk
High SPC values suggest issues in milk production practices.
Fill in the blank: Aseptically collected milk from clean, healthy cows generally has SPC values of less than ______.
1,000
Low SPC values are a sign of good milking practices.
What is one of the most frequent causes of high SPCs in raw milk?
Poor cleaning of the milking system
Residual milk on equipment provides nutrients for bacterial growth.
True or False: Regulatory requirements alone ensure the highest quality of raw milk.
False
Many in the dairy industry advocate for more stringent standards beyond regulatory requirements.
What practices might contribute to increased bulk-tank SPCs?
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.
What does the Preliminary Incubation Count (PIC) reflect?
Milk production practices
The PIC involves holding milk at 12.8°C (55°F) for 18 hours prior to plating.
How is the Preliminary Incubation Count (PIC) determined?
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.
What is generally considered a concerning PIC count?
> 50,000
This is regardless of the SPC.
What factors can lead to high Preliminary Incubation Counts (PICs)?
Failure to clean and sanitize the milking system, marginal cooling, prolonged storage times
Psychotrophic bacteria are often associated with high PICs.
What is the Lab Pasteurized Count (LPC)?
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.
What are thermoduric bacteria?
Bacteria that survive the pasteurization heat treatment
LPCs are generally much lower than SPCs, with counts > 200-300 deemed high.
What are common causes of high Lab Pasteurized Counts (LPCs)?
Chronic cleaning failures, significant levels of contamination from soiled cows, leaky pumps, old pipeline gaskets
Milkstone deposits can also contribute.
What does the Coliform Count procedure indicate?
It selects for bacteria associated with manure or environmental contamination
Coliforms may indicate fecal contamination but can also exist in the environment.
What is a concerning Coliform Count?
> 50
Counts above this level indicate poor milking hygiene or other contamination sources.
True or False: High coliform counts can only result from milking soiled cows.
False
They can also result from dirty equipment or environmental coliform mastitis.
Fill in the blank: The Preliminary Incubation Count (PIC) encourages the growth of bacteria that grow well at _______.
cool temperatures
What are the suggested bacterial test standards for quality premiums?
Standards include Standard Plate Count, Laboratory Pasteurization Count, Preliminary Incubation Count, and Coliform Bacteria Count
Refer to Table 1 for specific values.
What is the regulatory standard for Standard Plate Count?
< 200 - 300
No official standard set for Standard Plate Count.
What is the suggested standard for Coliform Bacteria Count?
< 50
California regulatory standard is < 750.
What are the three main sources of microbial contamination in raw milk?
- From within the udder
- From the exterior of the udder
- From milk handling and storage equipment
These sources influence the total bacteria count.
What factors influence microbial contamination of raw milk?
- 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.
What is the typical bacterial count in raw milk from healthy cows?
Less than 1000 total bacteria per ml
This count is considered low and typical for healthy cows.
How does mastitis affect bacterial counts in bulk milk?
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.
Which mastitis organisms most influence the total bulk milk count?
- Streptococcus agalactiae
- Streptococcus uberis
Other pathogens may also influence the bulk count.
True or False: The udder of healthy cows contributes significantly to the total bacteria count in bulk milk.
False
Healthy udders generally contribute very little to total bacteria count.
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.
cleaning and sanitizing
Proper procedures are essential to minimize contamination.
What is Staphylococcus aureus’s role in bulk tank counts?
Not thought to be a frequent contributor, though counts as high as 60,000/ml have been documented.
Reference: Gonzalez et al., 1986.
Does the presence of implied pathogens in milk indicate they originated from cows with mastitis?
No, they can occur due to factors like dirty cows and poor equipment cleaning.
Potential environmental mastitis pathogens can also contribute.
What does an increase in somatic cell count (SCC) indicate?
It can serve as supportive evidence that a mastitis bacterium may have caused an increase in milk.
Reference: Fenion et al., 1995.
How are correlations between somatic cell responses and environmental mastitis organisms described?
Correlations are found to be poor.
Includes coliform bacteria, streptococci, and certain coagulase-negative Staphylococcus spp.
What is significant about S. agalactiae and S. aureus in relation to milking equipment?
They are not thought to grow significantly on soiled milking equipment or under conditions of poor cooling.
What does the presence of specific mastitis organisms in bulk tank milk indicate?
Considered strong evidence that they originated from infected cows.
References: Gonzalez et al., 1986; Bramley and McKinnon, 1990.
Do mastitis organisms influence LPCs or PICs?
Generally, they do not influence LPCs or PICs, though coliform counts may be elevated in cases of coliform mastitis.
What microorganisms can contribute to microbial contamination from the exterior of the udder?
Microorganisms associated with skin and those derived from the cow’s environment.
Includes manure, mud, feeds, or bedding.
What is the impact of dirty cows on total bacteria counts?
Depends on the extent of soiling of the teat surface and wash procedures used before milking.
How can teat soil significantly affect total bacteria count in milk?
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.
What is an effective method for reducing microorganisms in milk from soiled teats?
Thorough cleaning of the teat with a sanitizing solution followed by drying with a clean towel.
What were the findings regarding coliform bacteria counts in untreated cows?
Coliform counts were relatively low, suggesting higher counts are likely due to other factors.
Factors include equipment and mastitis.
What factor is thought to influence total bulk milk bacteria count significantly?
The degree of cleanliness of the milking system.
Reference: Olson and Mocquat, 1980.
What can milk residues left on equipment contact surfaces do?
Support the growth of bacteria associated with contagious mastitis.
What is a significant source of microorganisms in dairy farming?
Water used on the farm
Particularly psychotrophs that may contaminate soiled equipment and milk.
What types of bacteria are often associated with environmental mastitis?
Coliforms
Certain strains can grow to significant numbers on milk contact surfaces.
What environmental contaminants are more likely to grow on soiled equipment surfaces?
Bedding, manure, feeds
These contaminants can lead to increased microbial growth.
What is the impact of old cracked rubber parts in dairy equipment?
Higher levels of thermoduric bacteria
These bacteria can persist despite cleaning efforts.
What cleaning practices tend to select for faster-growing organisms?
Less efficient cleaning, lower temperatures, absence of sanitizers
This leads to higher PICs and elevated LPCs.
Which sanitizers have been associated with reduced levels of psychotrophic bacteria?
Chlorine or iodine sanitizers
Effective use of these sanitizers minimizes bacterial growth.
What is the significance of psychotrophic bacteria in milk?
Associated with high PICs and found in higher count milk
Often due to neglect of proper cleaning or sanitizing procedures.
What effect does refrigeration storage have on milk?
Prevents growth of non-psychotrophic bacteria, selects for psychotrophic microorganisms
Contamination sources include soiled cows and dirty equipment.
What happens to psychotrophic bacteria populations if raw milk is held too long before processing?
They increase in numbers
Particularly if held near the legal limit of 7.2°C (45°F).
What is the result of holding milk at temperatures greater than 7.2°C (45°F)?
Rapid growth of bacteria other than psychotrophs
These bacteria can dominate raw milk.
What type of bacteria are historically associated with poor cooling of milk?
Streptococci
They appear as pairs or chains of cocci on microscopic examination.
What defect can certain strains of bacteria cause in milk?
A ‘malty defect’ with a distinct odor
This is associated with increased acidity in milk.
At what storage temperature do contaminants tend to proliferate?
Greater than 15°C (60°F)
This temperature encourages growth of specific bacterial contaminants.
Fill in the blank: Holding milk near _______ allows quicker growth of psychotrophic bacteria.
7.2°C (45°F)
This temperature threshold is critical for bacterial growth.
True or False: All psychotrophic bacteria are thermoduric.
False
Most psychotrophic bacteria do not survive pasteurization.
What is the effect of cooler temperatures of 1-2°C (34-36°F) on psychotrophic bacteria?
Delays the shift in microbial dominance
However, it does not prevent it indefinitely.
What is microbial contamination of raw milk?
Contamination from a variety of microorganisms from different sources.
What can high bacteria counts in raw milk result from?
A combination of factors such as dirty equipment and poor cooling.
What does SPC stand for in the context of raw milk testing?
Standard Plate Count.
What are some testing procedures used to evaluate the quality of raw milk?
LPC, PIC, coliform count.
What do the LPC and PIC tests target?
Bacteria that are contaminants, not the natural flora of the cow.
What is the purpose of bacterial culturing in the context of raw milk?
To identify mastitis bacteria.
What is the significance of a SPC greater than 10,000?
Indicates possible contamination from dirty cows, dirty equipment, or poor cooling.
True or False: High SPC counts are always due to mastitis.
False.
Fill in the blank: High coliform counts in raw milk are _______.
Possible but not likely.
What is the relationship between mastitis and bacterial counts in bulk tank milk?
High somatic cell counts can indicate mastitis bacteria presence.
List some sources of microbial contamination as detected by bacteriological procedures.
- Mastitis
- Dirty cows
- Dirty equipment
- Poor cooling
What does a high LPC count indicate?
Possible contamination.
What is the potential source of contamination when SPC is high but PIC does not increase?
Possible contamination from other sources.
Who authored the reference titled ‘Milk Under the Microscope’?
Atherton, H.V., and W.A. Dodge.
What does a coliform count being high indicate?
Possible contamination but not likely from mastitis.
Fill in the blank: The microbiology of raw milk is discussed in the book edited by _______.
R.K. Robinson.
