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Lab Test > Direct Microscopic > Flashcards

Direct Microscopic Flashcards

1
Q

What does the direct microscopic method allow analysts to examine in milk?

A

Numbers of bacterial clumps or somatic cells

This method is also known as the direct microscopic clump (DMC) count.

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2
Q

What can be evaluated simultaneously with the counting of bacterial clumps?

A

Morphology and arrangement of bacteria

This evaluation helps identify quality problems.

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3
Q

What do large numbers of bacterial clumps indicate?

A

Mastitis or other abnormal conditions of the udder

This is a significant indicator of udder health.

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4
Q

What term has come to replace ‘leucocytes’ in the context of somatic cells?

A

Somatic cells

This change reflects a more meaningful expression of body cells associated with the udder.

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5
Q

What is the official term for the microscopic method that counts somatic cells?

A

Direct microscopic somatic cell count (DMSCC)

This method is recognized for its research findings and application.

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6
Q

How were somatic cell counts previously estimated before the DMSCC?

A

By one of several other testing methods

These previous methods were less direct than the current microscopic approach.

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7
Q

What is the primary limitation of the direct microscopic method in pasteurized milk?

A

It is not used to determine compliance with finished standards

This is due to the generally low numbers of bacteria in pasteurized milk.

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8
Q

Why might the direct microscopic method still be useful in quality control?

A

Large numbers of bacteria in uncultured milk indicate unsanitary conditions

This applies regardless of whether the bacteria are viable.

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9
Q

Fill in the blank: The direct microscopic clump count is used to assess the _______ of milk.

A

Quality

This assessment can help identify potential health issues in dairy cows.

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10
Q

What does DMC stand for in the context of milk analysis?

A

Direct Microscopic Count

DMC is used to evaluate the bacterial contamination of raw milk or cream samples.

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11
Q

What is the primary purpose of evaluating the morphology of cells in milk samples?

A

To suggest the causes of high bacterial counts

This evaluation includes assessing the configuration of clumps and the presence of somatic cells.

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12
Q

True or False: Most dry milk contains a high number of viable bacteria.

A

False

Most dry milk contains relatively few viable bacteria.

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13
Q

What can microscopic examination of reconstituted dry milk samples provide?

A

Meaningful information on the previous sanitary history of the product

This examination can serve as a quality control measure.

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14
Q

What is the relative standard deviation (RSDR) in counts made on the same sample of milk?

A

3.7

This indicates potential for wide interlaboratory differences.

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15
Q

Fill in the blank: The number of somatic cells in raw milk provides a measure of the presence and extent of _______.

A

mastitis

Somatic cell counts help assess one aspect of raw milk quality.

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16
Q

What are the two types of counts mentioned in the context of milk analysis?

A
  • Direct Microscopic Counts
  • Direct Microscopic Somatic Cell Counts

These counts measure bacteria and somatic cells per milliliter or gram of dairy product.

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17
Q

What is the principle behind direct microscopic counts?

A

Bacteria or somatic cells are transferred to a slide, stained, and counted

This yields the number of cells per milliliter or gram of dairy product.

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18
Q

What type of immersion oil is preferred for microscopy in this context?

A

Type B (medium viscosity)

The refractive index should be 1.51 to 1.52 at 20°C.

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19
Q

What is the significance of using clear glass slides with etched surfaces?

A

They allow for confirmation of the correct reading area during analysis

This is important for achieving high accuracy.

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20
Q

How should slides be cleaned for repeated use?

A

Submerge in hot detergent solution and rinse thoroughly

Alternatively, use appropriate commercial alkaline and/or acid cleaners.

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21
Q

What instrument is mentioned for transferring 0.01-mL quantities?

A

Metal syringe

This instrument allows for rapid and convenient transfer but can create artifacts in milk films.

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22
Q

What should be done immediately after using a metal syringe?

A

Disassemble and clean the measuring tube and piston

This prevents residues from drying on the instrument.

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23
Q

What should be avoided when cleaning the syringe barrel and finger grip?

A

Do not submerge in detergents or solvents.

Proper maintenance prevents contamination and artifacts.

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24
Q

How should the interior of a syringe be cleaned?

A

Use forced suction or pressure with a rubber bulb and soapless detergent, then rinse with clean water and air-dry.

Acids, alkalis, and ordinary soap solutions should not be used.

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25
Q

What pH level should chemical cleaners be at when used for syringes?

A

At or near pH 7.0.

This ensures compatibility and safety for the syringe materials.

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26
Q

What is the first step before reassembling a syringe?

A

Ensure all detergent and milk residues are removed.

Proper cleaning is crucial for accurate results.

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27
Q

What precaution should be taken regarding syringe parts?

A

Do not interchange parts from one syringe with parts from another.

This prevents compatibility issues and maintains accuracy.

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28
Q

How often should syringes be tested for accuracy?

A

Annually.

Certification may be required by regulatory agencies.

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29
Q

What should be done if a syringe does not conform to specified milk deliveries?

A

Replace the syringe.

Ensures reliability in measurements.

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30
Q

How is the calibration of the volumetric load of a syringe determined?

A

By weight measurements of a representative test charge of milk.

This method ensures precision in delivery.

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31
Q

What is the average weight difference expected in a correctly calibrated syringe after multiple weighings?

A

0.0103 + 0.0005 g.

This value indicates proper calibration.

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32
Q

What are micro pipeters used for?

A

Measuring the 0.01-mL milk test portion.

They are preferred instruments due to their precision.

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33
Q

What is the purpose of a bent-point needle in milk testing?

A

Used for spreading milk or cream over a square centimeter area.

This facilitates even distribution for analysis.

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34
Q

What temperature range is recommended for drying films?

A

40° to 45°C.

Uniform heat distribution is important for consistent results.

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35
Q

What type of microscope is preferred for milk analysis?

A

A binocular microscope with a 1.8-mm oil-immersion objective.

Additional features include an Abbe condenser and a numerical aperture of 1.25 or higher.

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36
Q

What is the recommended magnification for oculars in milk testing microscopes?

A

10x magnification is recommended, with 12.5x to 15x permitted.

This ensures sufficient detail for analysis.

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37
Q

What is the significance of the microscopic factor (MF) in milk analysis?

A

It determines the amount of milk that can be examined in any one field.

MFs are used to calculate bacterial clumps or somatic cells per field.

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38
Q

What should be ensured about the surface for drying films?

A

It should be clean, dust-free, and level.

A regulated heat source is also necessary.

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39
Q

Fill in the blank: Syringes should be cleaned before _______.

A

first use.

40
Q

True or False: It is acceptable to use ordinary soap solutions for cleaning syringes.

A

False.

Ordinary soap solutions can damage the syringe.

41
Q

What should be adjusted for individuals using paired oculars in microscopy?

A

Diaphragms must be specially adjusted for the individual

Counts must be corrected based on the diameter of the field observed.

42
Q

What is the significance of constant tube length in microscopes?

A

It keeps the resultant calibrated field and magnification constant regardless of changes in interpupillary settings.

43
Q

What is the MF in microscopy?

A

Magnification Factor

It is calculated based on the field diameter observed.

44
Q

How is the Magnification Factor (MF) calculated?

A

MF = 3.1416 x d² / 40,000

‘d’ is the diameter measured under the oil-immersion objective.

45
Q

What is the formula to express the MF?

A

Express the MF to 2 significant figures.

46
Q

What does the reciprocal of the MF represent?

A

The fraction of 1 mL of milk observed in 1 microscopic field.

47
Q

What is the purpose of the ocular disc in microscopy?

A

To subdivide the field for counting purposes.

48
Q

What type of stage is required for microscopy?

A

A regular mechanical stage or a special stage for specific slide sizes.

49
Q

What is a stage micrometer slide used for?

A

To measure field diameter accurately.

50
Q

What is a hand tally used for in microscopy?

A

To count cells or particles observed.

51
Q

At what temperature should samples be warmed before testing for DMSCC?

A

40°C.

52
Q

How should samples be mixed before preparing films?

A

Shake 25 times in 7 seconds with a 1-foot movement.

53
Q

What is the maximum time to allow foam to disperse after mixing?

A

No more than 3 minutes.

54
Q

What is essential for cleanliness when preparing films?

A

Instruments and glassware must be scrupulously clean.

55
Q

What is the drying temperature range for films?

A

40° to 45°C.

56
Q

What should be done with the measuring tube before each use?

A

Rinse it in fresh tap water.

57
Q

What is the correct technique for using a 0.01-mL syringe?

A

Dip the tip slightly below the surface and repeatedly draw in and expel water.

58
Q

What should be avoided when wiping the tip of the syringe?

A

Do not wipe over the tip.

59
Q

What is the procedure for using micro pipeters?

A

Use a separate tip for each sample and avoid foam.

60
Q

What should be done with used tips from micro pipeters?

A

Discharge into disinfectant or biohazard bags.

61
Q

What is a key consideration during film preparation to prevent contamination?

A

Protect films from exposure to dirt, dust, and insects.

62
Q

What should be done with a clean bent-point dissecting needle between samples?

A

Wipe the needle on a clean, dry tissue or towel

63
Q

At what temperature should the milk film be dried?

A

40° to 45°C

64
Q

What is the recommended method for handling multiple slides during staining?

A

Use holders of glass, stainless steel, or other suitable material

65
Q

What should be avoided when preparing stains?

A

Using liquid reagents that contain suspended foreign matter

66
Q

Which three stains may be used for cow’s milk?

A
  • LW/NL-T stain
  • LW/NL-X stain
  • LW/NL-F stain
67
Q

What is the issue with the LW/NL-T stain when used for goat’s milk?

A

It has produced highly variable results and is unreliable for somatic cell count

68
Q

What is a suitable replacement for staining somatic cells in goat’s milk?

A

Pyronin Y methyl green stain with Carnoy’s fixative

69
Q

What are the components for the LW/NL-T stain?

A
  • 0.6 g of certified methylene blue chloride
  • 52 mL of 95% ethyl alcohol
  • 44 mL of tetrachlorethane
  • 4 mL of glacial acetic acid
70
Q

How long should the LW/NL-T stain solution stand?

A

12 to 24 hours at 44° to 72°C

71
Q

What is the difference in the preparation of LW/NL-X stain compared to LW/NL-T stain?

A

LW/NL-X uses xylene instead of tetrachlorethane and 0.5 g of methylene blue chloride

72
Q

What is included in the Canadian modification of the modified Newman-Lampert stain?

A

Basic fuchsin dye

73
Q

What are the components for Carnoy’s fixative?

A
  • 60 mL of chloroform
  • 20 mL of glacial acetic acid
  • 120 mL of 100% ethyl alcohol
74
Q

What should be done with the pyronin Y stain before use?

A

Filter through Whatman No. 1 paper

75
Q

How should dried, stained slides be rinsed after staining?

A

In 3 changes of tap water at 35° to 45°C

76
Q

What is the requirement for the New York modification of the pyronin Y-methyl green stain procedure?

A

Use of a fume hood

77
Q

How long should a prepared film be fixed in Carnoy’s fixative?

A

5 minutes

78
Q

What should be done with used staining solutions?

A

Discard them whenever they become contaminated or unsuitable

79
Q

How should slides be stored after examination?

A

In dust-free, slide-storage boxes

80
Q

What can interfere with the staining procedure or future re-examination of milk films?

A

Accumulation of pencil marks on slides

81
Q

What is the criteria for counting bacteria in separate clumps?

A

Count as separate clumps if 2 cells or clumps are separated by a distance equal to or greater than twice the smallest diameter of the 2 cells nearest each other.

82
Q

What cells are counted in DMSCCs?

A

Only somatic cells with an identifiable stained nucleus.

83
Q

What color is the stained nucleus in bovine somatic cells?

A

Dark blue.

84
Q

What color is the stained nucleus in caprine somatic cells?

A

Blue or blue-green.

85
Q

How do you count polymorphonucleated cells?

A

Count as a single cell if it has two or more discernible nuclear lobes.

86
Q

What is the minimum diameter for a nucleus to be counted?

A

8 microns.

87
Q

What is the formula to calculate the area of a single strip in the counting method?

A

Area of a single strip (mm²) = 11.28 mm x D (in mm).

88
Q

How do you determine the number of single strips in a 0.01-mL milk film?

A

Number of single strips = 100 mm² / area of single strip.

89
Q

What is the Single Strip Factor (SSF)?

A

SSF = Number of strips in 0.01 mL x 100.

90
Q

What is the counting procedure for a single-strip count?

A

Focus on the film edge, traverse the diameter, counting cells within the strip and those touching one edge.

91
Q

How is the count per milliliter calculated?

A

Count per milliliter = Number of somatic cells and/or bacterial clumps in a single strip x SSF.

92
Q

What is the importance of analyst training in counting accuracy?

A

The training and skill of the analysts are crucial for accuracy, precision, and reproducibility.

93
Q

What are some factors responsible for variations in counts?

A
  • Inaccuracy in measuring samples * Faulty preparation and staining * Minute amount of milk examined * Irregular distribution of cells * Poor microscopy * Eye fatigue * Analyst inexperience.
94
Q

How should counts be reported?

A

Report counts only to the first 2 left-hand digits of the estimate, followed by the appropriate number of zeroes.

95
Q

What is the rule for rounding when the third digit is 5?

A

If the second digit is odd, round up; if even, round down.

96
Q

What should be done with slides that have violative counts?

A

Save slides for future reference.

Lab Test (13 decks)

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