EFFECT OF PLATE INCUBATION TEMPERATURE ON BACTERIAL COUNTS OF GRADE A RAW MILK1

1973 ◽  
Vol 36 (3) ◽  
pp. 152-154 ◽  
Author(s):  
H. E. Randolph ◽  
B. K. Chakraborty ◽  
Otto Hampton ◽  
D. L. Bogart
Keyword(s):  
Incubation Temperature ◽  
Statistical Significance ◽  
Correlation Coefficients ◽  
Raw Milk ◽  
Plate Count ◽  
Bacterial Counts ◽  
Standard Plate Count ◽  
Standard Plate ◽  
The Mean ◽  
Incubation Temperatures

Bacterial counts on 155 raw milk samples obtained with plate incubation temperatures of 27 and 32 C were closely correlated (r = 0.96) . Correlation coefficients between counts obtained at both 27 and 32 C and psychrotrophic (7 C-10 days) counts for all samples were relatively low, but statistically significant ( P < 0.01). The correlation to psychrotrophic counts was especially low and in some instances lacking in statistical significance in the sample groups with counts ( 27 and 32 C) <100,000/ml. Eighty-four of the samples had higher counts at 32 C and 62 samples had higher counts at 27 C. The mean psychrotrophic count of the samples with higher counts at 27 C was higher than the mean psychrotrophic count of the other samples. However, the correlation coefficients were higher for samples with counts higher at 32 C. Incubation at 27 C does not appear to offer significant advantages over the 32 C incubation temperature used in the Standard Plate Count.

MICROBIAL COUNTS OF INDIVIDUAL PRODUCER AND COMMINGLED GRADE A RAW MILK1

1973 ◽  
Vol 36 (3) ◽  
pp. 146-151 ◽  
Author(s):  
H. E. Randolph ◽  
B. K. Chakraborty ◽  
Otto Hampton ◽  
D. L. Bogart
Keyword(s):  
Statistical Significance ◽  
Correlation Coefficients ◽  
Raw Milk ◽  
Microbial Populations ◽  
Plate Count ◽  
Microbial Counts ◽  
Standard Plate Count ◽  
Standard Plate ◽  
Bulk Tank ◽  
Highly Correlated

Microbial populations of Grade A raw milk samples from 105 individual producers and 74 bulk tank trucks (commingled) were enumerated by Standard Plate Count (SPC), psychrotrophic count (PBC), coliform count (CC), laboratory pasteurized count (LPC), thermophilic count (TBC), yeast and mold count (Y&M), and special penicillin (PEN) and crystal violet tetrazolium (CVT) agar count procedures. In addition, microbial populations were determined by the SPC, PBC, PEN, and CVT procedures after preliminary incubation (PI) of samples. Initial mean counts obtained on individual producer samples were generally lower than those for commingled samples. However, producer samples had higher mean counts after PI. Growth ratios were lower for commingled than for individual producer samples indicating slower growth during PI. Results obtained by the PBC, PEN, and CVT procedures were similar when viewed as correlation coefficients, distribution of samples according to microbial counts, mean counts, and growth ratios during PI. Before PI, the correlation between these three tests was poor and lacked statistical significance when the PBC was <50,000/ml. After PI, the tests were highly correlated (P<0.01) and the r values ranged from 0.8 to 0.9 for samples with PBC levels above 108/ml.

Evaluation of the 3M Dry Medium Culture Plate (Petrifilm™ SM) Method for Determining Numbers of Bacteria in Raw Milk1

1984 ◽  
Vol 47 (10) ◽  
pp. 753-755 ◽  
Author(s):  
R. E. GINN ◽  
V. S. PACKARD ◽  
T. L. FOX
Keyword(s):  
Cold Water ◽  
Correlation Coefficients ◽  
Raw Milk ◽  
Water Soluble ◽  
Gelling Agent ◽  
Plate Count ◽  
Suitable Alternative ◽  
Standard Plate Count ◽  
Standard Plate ◽  
Indicator Dye

The 3M Company has developed a sample-ready system (Petrifilm ™ SM) for enumerating bacteria in milk and other food products. The testing unit consists of Standard Methods culture medium coated onto a base film and overlaid with a second film coated with a cold-water-soluble gelling agent and tetrazolium indicator dye. As such, the system is ready to accept samples of product. A pipette or 0.001-ml plate loop continuous pipetting syringe can be used for applying samples. In this study, both methods of sample addition were used and results compared with those of the Standard Plate Count (SPC) and standard Plate Loop (PL) methods for determining bacteria numbers in raw milk. In total, 108 samples were analyzed in duplicate by each of the four methods. The correlation coefficients (r) between the 3M-SPC and SPC, 3M-PL and PL, 3M-PL and SPC and PL and SPC were 0.946, 0.935, 0.941, and 0.974, respectively. Repeatability, as measured by mean log10 variance for duplicate determinations, was essentially the same for the four methods, and in all instances less than 0.005. The mean log10 differences between the SPC and 3M-SPC, and SPC and 3M-PL were, respectively, −0.177 and −0.168. The preceding statistical criteria suggest the Petrifilm™ SM method to be a suitable alternative to the SPC or the PL procedure.

Preliminary Incubation Count as an Index of Raw Milk Microbiological Quality During Storage

1984 ◽  
Vol 47 (3) ◽  
pp. 206-208 ◽  
Author(s):  
J. J. RYAN ◽  
R. H. GOUGH ◽  
C. H. WHITE
Keyword(s):  
Microbiological Quality ◽  
Storage Period ◽  
Raw Milk ◽  
Plate Count ◽  
Bacterial Counts ◽  
Sample Group ◽  
Psychrotrophic Bacteria ◽  
Standard Plate Count ◽  
Milk Samples ◽  
Standard Plate

During a 5-month period, 200 raw milk samples were collected from two Louisiana milk plants. Standard Plate Count (SPC), Psychrotrophic Bacteria Count (PBC), and Proteolytic Count (PC) of each sample were initially determined, then monitored daily during a 5-d storage period at 2.2°C. As hypothesized, all bacterial counts increased during the storage period. The magnitude of the increase in bacterial numbers during storage was further investigated by dividing the milk samples into bacteriologically acceptable and unacceptable groups based on SPC or Preliminary Incubation (PI) count. An SPC of 1.0 × 105/ml and PI counts of 1.0 × 105/ml, 1.5 × 105/ml, 2.3 × 105/ml, and 3.0 × 105/ml were used to repeatedly dichotomize the 200 raw milk samples into two groups. Median SPC, PBC, and PC for each acceptable and unacceptable group were then calculated. Dichotomization based on PI counts yielded acceptable sample groups having consistently lower bacterial counts during storage than did the acceptable sample group, which resulted from the dichotomization based on a SPC of 1.0 × 105/ml. The results of this study indicated that the PI count is of considerable value for raw milk quality control.

Effect of Five Surface Area-to-Sample Volume Ratios During Preliminary Incubation on The Bacterial Count of Raw Milk1,2

1979 ◽  
Vol 42 (12) ◽  
pp. 968-970
Author(s):  
J. A. RITTER ◽  
B. E. LANGLOIS ◽  
J. O'LEARY
Keyword(s):  
Surface Area ◽  
Incubation Temperature ◽  
Bacterial Count ◽  
Raw Milk ◽  
Sample Volume ◽  
Bacterial Counts ◽  
Milk Samples ◽  
Standard Plate ◽  
Plate Counts ◽  
Incubation Temperatures

Effects of ratio of surface area to volume of sample during preliminary incubation (PI) and of different plate incubation temperatures on bacterial counts of raw milk samples were studied. One hundred and twenty Grade A raw milk samples collected during a 10-month period were divided into five 100-ml aliquots and allotted to one of five surface area to volume ratios. The ratios during PI ranged from 0 cm2/100 ml to 149.74 cm2/100 ml. Following PI, pour plates of each treatment were incubated at 26, 30 and 32 C for 72 h. The Standard Plate Counts (SPC) ranged from 89 × 101 to 20 × 108/ml, with the SPC of 73.6% of the samples being less than 1 × 105/ml. Counts after PI tended to be higher as the plate incubation temperature decreased from 32 to 26 C and as the ratio of surface area to volume of sample increased. None of the differences between the counts for the 15 treatment-incubation temperatures was significant. Counts of 61 samples increased less than one log count during PI, while counts of 33 and 16 samples increased one to two log counts and over two log counts, respectively. The greater the SPC, the smaller the increase in count during PI. Of the 81 samples with SPC less than 1 × 105/ml, 29 had counts after PI that exceeded 2 × 105/ml.

EFFECT OF TEMPERATURE AND TIME OF PLATE INCUBATION ON THE ENUMERATION OF PASTEURIZATION-RESISTANT BACTERIA IN MILK1

1963 ◽  
Vol 26 (11) ◽  
pp. 357-363 ◽  
Author(s):  
W. R. Thomas ◽  
G. W. Reinbold ◽  
F. E. Nelson
Keyword(s):  
Incubation Temperature ◽  
Bacterial Count ◽  
Raw Milk ◽  
Effect Of Temperature ◽  
Plate Count ◽  
Resistant Bacteria ◽  
Pasteurized Milk ◽  
Standard Plate Count ◽  
Standard Plate

This study was undertaken to determine the effect of temperature and time of plate incubation upon the count of thermoduric bacteria in milk. Specific types of thermoduric bacteria in pure culture, as well as those present in the mixed flora of commercial milk samples, were enumerated. Plate incubation at 28 C for 4 days was the temperature-time combination that produced the highest thermoduric bacterial count with laboratory-pasteurized milk. Incubation at 21, 32 or 35 C gave lower counts. Thermoduric bacteria subjected to pasteurization were more exacting in their growth temperature requirements than were unheated bacteria. Cultures of Arthrobacter sp., Micrococcus varians and Streptococcus sp. grew over a much wider temperature range before laboratory pasteurization than after the heat treatment. The incubation temperature and time currently recommended for the standard plate count, while presumably adequate for the enumeration of bacteria in raw milk, may not be equally satisfactory for the determination of the maximum viable bacterial population of pasteurized milk.

PREDICTION OF STANDARD PLATE COUNT OF MANUFACTURING-GRADE RAW MILK FROM THE PLATE LOOP COUNT1

1970 ◽  
Vol 33 (4) ◽  
pp. 168-170 ◽  
Author(s):  
Earl O. Wright ◽  
George W. Reinbold ◽  
Leon Burmeister ◽  
James Mellon
Keyword(s):  
Raw Milk ◽  
Plate Count ◽  
Adjustment Factor ◽  
Bacterial Counts ◽  
Standard Plate Count ◽  
Milk Samples ◽  
Count Range ◽  
Standard Plate ◽  
Plate Counts

Plate Loop Counts and Standard Plate Counts of manufacturing grade raw milk samples were compared. With bacterial counts of 200,000/ml and less, the Plate Loop Count approximated the Standard Plate Count very closely. With counts greater than 200,000, the agreement was not as close. Differences between counts from the two methods, however, were not statistically significant (P<0.05) within either count range. An adjustment factor was determined to enable the Plate Loop Count to more accurately predict the Standard Plate Count of milk with a Standard Plate Count >200,000/ml. The Standard Plate Count can be reasonably predicted from the Plate Loop Count by the formula:

EVALUATION OF PRODUCTION CONDITIONS OF MANUFACTURING-GRADE RAW MILK BY FIELDMEN RATINGS AND BY BACTERIAL TESTS

1971 ◽  
Vol 34 (4) ◽  
pp. 200-203 ◽  
Author(s):  
Roger Dabbah ◽  
W. A. Moats ◽  
J. C. Olson
Keyword(s):  
Correlation Coefficients ◽  
Raw Milk ◽  
Plate Count ◽  
Standard Plate Count ◽  
Reduction Test ◽  
Sanitary Condition ◽  
Methylene Blue Reduction ◽  
Standard Plate ◽  
Microscopic Count ◽  
Production Conditions

Standard microbiological tests, Standard Plate Count, direct microscopic count, methylene blue reduction test, and several variations of the resazurin reduction test were correlated with fieldmen's ratings of sanitary condition of milking area, milk house, and milking utensils. Correlation coefficients were low, in general, approximately 0.2. The effect of different production facilities and practices on these correlations was variable. Results suggest that bacterial tests and fieldmen's inspection be used concurrently since they appear to measure different sanitary factors on the producing farms.

Effect of Various Combinations of Medium, Diluent and Incubation Conditions on Recovery of Bacteria from Manufacturing Grade and Grade A Raw Milk1

1977 ◽  
Vol 40 (4) ◽  
pp. 222-227 ◽  
Author(s):  
B. E. LANGLOIS ◽  
CHAMRAS SANGHIRUM
Keyword(s):  
Incubation Temperature ◽  
Raw Milk ◽  
Ringer Solution ◽  
Plate Count ◽  
Distilled Water ◽  
Standard Methods ◽  
Standard Plate Count ◽  
Milk Samples ◽  
Peptone Water ◽  
Standard Plate

Recovery of microorganisms from manufacturing grade and Grade A raw milk was determined using 18 plating combinations which consisted of three media, three diluents, and two incubation temperatures. Plating conditions specified in Standard Methods for doing the Standard Plate Count was one of the 18 combinations used. Combinations studied consisted of Standard Methods Agar, Schaedler Agar, and Eugonagar as plating medium; phosphate buffered distilled water, 0.1% peptone water, and Ringer solution as diluent; and 28 C for 72 h and 32 C for 48 h as incubation temperature. Forty manufacturing grade and 40 Grade A raw milk samples were plated using each of the 18 combinations. Highest mean counts were obtained for both grades of milk with the combination of Standard Methods Agar, phosphate buffered distilled water, and 28 C for 72 h. Samples, diluents, media, and samples × diluents interaction had a highly significant (P<.01) effect on counts of manufacturing grade milk samples; while samples, media, and temperatures had a highly significant (P<.01) effect on counts of the Grade A raw milk samples. Nonsignificant differences were obtained in counts of the manufacturing gradesamples with eight of 17 plating combinations when compared with counts obtained with Standard Methods. Counts for Grade A samples obtained with six of 17 combinations were similar to counts obtained with Standard Methods.

A STATISTICAL EVALUATION OF THE 3M BRAND AUTOMATIC COLONY COUNTER1,2

1974 ◽  
Vol 37 (8) ◽  
pp. 435-437 ◽  
Author(s):  
V. S. Packard ◽  
Roy E. Ginn
Keyword(s):  
Statistical Evaluation ◽  
Raw Milk ◽  
The Other ◽  
Total Variance ◽  
Plate Count ◽  
Standard Plate Count ◽  
Culture Plate ◽  
Counter Model ◽  
Standard Plate ◽  
Colony Counter

The 3M Brand Automatic Colony Counter, Model 620, was evaluated and compared with three laboratory technicians on raw milk Standard Plate Count (SPC) cultures over the range of counts from 0–300 colonies per culture plate. Overall, the estimated total variance for the three technicians was 15.07, for the 3M unit 17.82. On plates averaging greater than 150 colonies the 3M unit and hand counts were about equal in Variability. On lower counts the 3M device was somewhat more variable, although within what would appear to be acceptable limits. For the range of data studied, 99.4% of the variance (for the average of three counts by either method) could be accounted for by a similar average of observations using the other method. The 3M unit averaged 2.33 counts higher than technician counts.

Evaluation of Dry Sheet Medium Culture Plate (Compactdry TC) Method for Determining Numbers of Bacteria in Food Samples

2000 ◽  
Vol 63 (5) ◽  
pp. 665-667 ◽  
Author(s):  
SHINGO MIZUOCHI ◽  
HIDEMASA KODAKA
Keyword(s):  
Cold Water ◽  
Correlation Coefficients ◽  
Food Samples ◽  
Water Soluble ◽  
Gelling Agent ◽  
Plate Count ◽  
Aerobic Bacteria ◽  
Suitable Alternative ◽  
Standard Plate Count ◽  
Standard Plate

The Compactdry, a ready-to-use and self-diffusible dry medium sheet culture system, has been developed by the Nissui Pharmaceutical Co. Ltd. for enumerating bacteria in food. The Compactdry consists of special spread sheet with culture medium that is the same as standard method nutrients, a cold water-soluble gelling agent, and a unique plastic dish. The procedure for bacterial examination in a sample solution (1 ml) is to just inoculate a test solution into the center of the self-diffusible medium and incubate at 35°C for 48 h. The Compactdry TC (CTC) for the enumeration of total aerobic bacteria from 97 food samples was compared with the standard plate count (SPC) method and 3M Petrifilm aerobic count plates (PAC). The correlation coefficients between the CTC and SPC method, the CTC and PAC, and the PAC and SPC method were 0.97, 0.99, and 0.97, respectively. The Compactdry system is useful for the enumeration of total aerobic bacteria in food and may be a possible suitable alternative to the conventional pour-plate or the Petrifilm plate methods.

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