Lab Test Flashcards
What is one of the best tools available for the dairy fieldman?
The microscope
The microscope is used to study bacterial types in milk.
What can careful study of bacterial types in milk tell you?
Much about its bacterial quality
This analysis is important for assessing milk safety and quality.
What type of reference have dairy fieldmen often requested?
A collection of photomicrographs
These images assist in the microscopic evaluation of milk.
What do stained smears indicate in milk evaluation?
The history of a milk sample
They are useful but should not be the sole criterion for quality.
True or False: No single test can provide a complete picture of the bacteriological history of milk.
True
Multiple tests are necessary for thorough evaluation.
What can affect the meaningfulness of deductions about milk quality?
Accurate sampling and proper care of milk samples
Poor practices can lead to misleading results.
What are vacuoles in milk caused by?
The removal of fat droplets from the dried milk solids
They appear as white circular areas against a blue background.
What should good quality milk never show in large numbers?
Leucocytes or bacterial cells
Occasional presence is acceptable, but not in large quantities.
What is a characteristic of mastitis milk?
Presence of long-chain Streptococcus agalactiae and associated leucocytes
These indicate infection and poor milk quality.
What can the use of a strip cup reveal in mastitis milk?
Flaky particles (garget)
This is a sign of milk quality issues due to udder damage.
Fill in the blank: Good quality milk may contain an occasional _______ or bacterial cell.
leucocyte
Good quality milk should not have large numbers of these cells.
What type of streptococci is associated with massive numbers of leucocytes in milk?
Short-chain streptococci and long-chain Streptococcus agalactiae
These organisms indicate an infection that may affect milk production in cows.
What is phagocytosis?
The actual engulfing of bacterial chains by leucocytes
This process is part of the immune response to destroy pathogens.
In mastitis-infected cows, how many quarters may yield infected milk?
One or two quarters
The remainder of the udder may still produce normal milk.
What characteristic grouping is typical of staphylococci?
Irregular groupings resembling a clump of grapes
This morphology is indicative of staphylococcal infection.
What are the common sources of staphylococci contamination in milk?
Contact with residues in open seams and crevices of utensils
Poor sanitation practices lead to contamination from milking equipment.
What may cause the presence of clumps of staphylococci in milk?
Improperly cleaned milking machines or rubber parts
Hygiene practices are crucial to prevent bacterial contamination.
What type of cell growth is associated with contaminated utensils?
Mixed cell growth
This includes clumps of staphylococci, diplococci, yeasts, rods, and chains.
What can cause the same bacterial picture as contaminated utensils in milk?
Contamination by dust
Environmental factors can also contribute to milk contamination.
What do paired round cells (diplococci) or short chains of round cells (streptococci) indicate in milk?
Poor cooling
This is typically associated with Streptococcus lactis, the sour-milk organism.
What does a milk sample on the verge of souring show under the microscope?
Many pairs of cells, double pairs, and short chains with a high bacterial count
This indicates that the milk is almost sour.
What does a mixed bacteria field in milk suggest?
Poor production methods
It shows clumps of micrococci, short chains, and paired bacilli, indicating contamination.
What impact does contamination have on milk quality?
It can ruin the quality of a large volume of milk
The lowered quality persists in pasteurized or manufactured products.
Fill in the blank: The presence of _______ in milk usually indicates poor cooling.
paired round cells (diplococci)
True or False: A sample showing a variety of bacteria is a good sign of milk quality.
False
A variety of bacteria suggests poor production methods.
What is indicated by the presence of large numbers of paired cells or diplococci in milk?
Evidence of poor cooling and mixed bacteria
This condition leads to actively growing organisms and off-flavors.
What type of organisms are indicated by contamination from hay and dirt?
Heavy, paired, rod-shaped organisms
These are spore-formers and quite heat resistant.
True or False: Poor cooling in milk can lead to quick spoilage.
True
Poor cooling allows for contamination and growth of spoilage organisms.
What do filter pads remove from milk?
Visible particles of manure or manure-contaminated soil or bedding
However, organisms can still pass through the filter.
What is the consequence of manure contamination in milk?
Breakdown of milk proteins leading to off-flavors and sweet curdling
Short rods from manure can separate from solid particles.
Fill in the blank: The presence of _______ in milk indicates contamination by organisms from hay and soil.
large bacilli
What characteristic of heavy, paired rod-shaped organisms indicates they are spore-formers?
Heat resistance
This trait allows them to survive in various conditions.
What happens when milk is contaminated with actively growing organisms?
It develops off-flavors
This is often a result of poor cooling and mixed bacteria.
What type of contamination is indicated by heavy sediment in milk?
Dust contamination
This can come from manure and affects milk quality.
What is the typical arrangement of four micrococci often associated with milkstone called?
Tetrads
Tetrads are heat loving and may originate from the teat canal.
How resistant are tetrads to germicidal agents?
Relatively resistant
Tetrads are generally considered inert and cause little if any damage to the milk.
What type of bacteria are short, rod-shaped with rounded ends commonly associated with?
Soil
These bacteria may enter milk through a contaminated water supply.
What indicates poor production practices in milk?
Large numbers of short, rod-shaped bacteria
A few of these bacteria are normally present in raw milk.
What condition can be caused by some short, rod-shaped bacteria?
Acute and chronic mastitis
These bacteria may produce an acute form of mastitis and occasionally chronic infections.
What is the mild form of mastitis associated with staphylococci called?
Nonspecific mastitis
Laboratory analyses are needed to determine the pathogenicity of staphylococci.
What do mastitic staphylococci appear like under the microscope?
Similar to those in milk contaminated by dirty utensils
They are typically accompanied by more leucocytes than normal.
What are yeast cells typically like in shape?
Normally spherical or slightly elongated
Yeast cells frequently show small buds and are larger than bacteria cells.
Why are yeasts normally present in milk?
Due to contamination by dirty rubber parts in milking machines
Yeasts may also invade in cases of mastitis, though this is not common.
What effect do yeasts have in cheese and milk?
They produce a gassy, yeasty breakdown
This breakdown occurs more frequently in cheese than in milk.
What are the characteristics of mold contamination in fresh milk?
Not commonly found unless in contact with moldy scum of milk solids
Neglected rubber parts can also cause mold contamination.
What are the advantages of direct microscopic examination of milk?
Rapid, inexpensive, and slides can be preserved for review
Dead bacterial cells stain differently than live ones, providing insights into milk quality.
What can be deduced by reviewing a series of fields of a milk sample under a microscope?
Valuable index of the relative number of several types of bacteria present
This helps evaluate a producer’s quality program.
True or False: It is common to obtain milk samples with only one type of bacteria present.
False
Under farm conditions, milk samples usually contain multiple types of bacteria.
What is essential to know in order to evaluate the evidence obtained with a microscope?
All of the conditions under which milk is produced at a farm
This knowledge is crucial for accurate evaluation.
Fill in the blank: Properly used, the microscope can greatly decrease the time spent on each _______.
quality call
This efficiency is important for laboratory workers and fieldmen.
