142. Van Oijen Modification of the Frost Little Plate Method. A Critical Investigation of van Oijen's Test for the Bacterial Content of Milk Samples

1936 ◽  
Vol 7 (3) ◽  
pp. 244-257 ◽  
Author(s):  
H. Barkworth
Keyword(s):  
Random Distribution ◽  
Plate Count ◽  
Plate Method ◽  
High Count ◽  
Actual Distribution ◽  
Plate Test ◽  
Milk Samples ◽  
Counting Error ◽  
Colony Counting ◽  
Bacterial Content

1. Van Oijen's modification of the Frost Little Plate method for estimating the bacterial content of milk has been examined and compared with the plate count.2. The colony counting error of the Van Oijen test is about the same as that of the plate count.3. From the results of quintuplicate tests it is recommended that 24 hours' incubation at 28°C. be used for the Van Oijen test and 72 hours at 37° C. for the plate test.4. Thirty-one low-count samples (3000–30,000 per ml.) and thirty-one high-count samples (30,000–300,000 per ml.) were tested in quintuplicate by both methods, and statistical examination of the results shows that at both levels of count the Van Oijen test is significantly more accurate. The Van Oijen results are on the average 1–3 per cent log lower than the plate count and this difference is found to be significant.5. In the Van Oijen test the results are based on a larger amount of milk than the plate test, and a method is given for testing whether the increased accuracy exceeds the expectation owing to increased size of sample.6. It is noted that failure of replicate tests to reflect random distribution may be due to the variability of the technique as much as to irregularities in the actual distribution of the bacteria in the sample.7. The effect of size of sample upon reproducibility is discussed. A true comparison of the accuracy of various methods for assessing the bacteria content of milk samples cannot be obtained unless allowance is made for variation in size of sample as between different techniques.

THE QUALITY OF RAW MILK FROM SELECTED OHIO MARKETS.

1966 ◽  
Vol 29 (4) ◽  
pp. 118-121 ◽  
Author(s):  
S. P. Ohri ◽  
W. L. Slatter
Keyword(s):  
Raw Milk ◽  
Plate Count ◽  
High Count ◽  
Coliform Count ◽  
Standard Plate Count ◽  
Milk Samples ◽  
Bacteriological Method ◽  
Standard Plate ◽  
Bulk Tank

Summary An 8-month survey of the bacteriological quality of bulk tank produced fluid milk supplies for four major markets in Ohio, was made utilizing the Standard Plate Count (SPC), the preliminary incubation count (PI), the thermoduric (pasteurized milk) count, and the coliform count. In terms of maximum standards of 200,000 and 100,000 organisms/ml, the SPC would have eliminated 13% and 20% of the milk samples, respectively. A SPC of 50,000/ml, a PI count of 200,000/ml, a thermoduric count of 500/ml, and a coliform count of 100/ml would have eliminated 37%, 34%, 40%, and 40%, respectively, of the samples but not all of the samples eliminated by one test were eliminated by another test. All of the tests employed showed a seasonal trend especially in the high count categories but the trend was less noticeable in the results of the preliminary incubation count. A combination of two of the methods was superior to any single bacteriological method employed in detecting unsatisfactory milk. Of the tests used, the combination of the thermoduric count (500/ml) and the coliform count (100/ml) was the most effective in the detection of unsatisfactory milk samples.

Methods of Determining the Numbers of Bacteria in Milk

1930 ◽  
Vol 1 (2) ◽  
pp. 111-135 ◽  
Author(s):  
A. T. R. Mattick
Keyword(s):  
Previous History ◽  
Standard Technique ◽  
Point Of View ◽  
Plate Count ◽  
Accurate Information ◽  
Plate Method ◽  
Large Sphere ◽  
Keeping Quality ◽  
History Of ◽  
Bacterial Content

SummaryOne fact emerges from a consideration of the literature upon the methods at present in use for determining the bacteriological content of milk, viz. no one method is capable of giving exact information as to the numbers of living bacteria present.The plate count has been shown to be subject to a number of limitations to its accuracy, but it is possible that these are much more the result of failure to appreciate the importance and effect of observing the protocols of a standard technique, than of insurmountable causes of error inherent in the method. Any one laboratory should be able to return results which are comparable from sample to sample, but as has been shown, it is unlikely that results will agree between laboratory and laboratory unless the most rigid precautions to secure uniformity are enforced. This latter fact does not seem to be of very great importance, since the most that can be expected is that results shall reflect the condition of the milk at the time of examination. These will be governed by the previous history of the milk. Figures have been given which show (p. 120) that, if milk is properly produced and handled, the bacterial content will be, even 24 hours or more after milking, within the range where the plate count as a method of computation is more reliable than any other known method.From the point of view of keeping quality and value for some manufacturing purposes, milk is either good or bad, and the obvious inaccuracy of the plate or any other method is a matter of small importance when the bacterial content has once exceeded 500,000 per 1 c.c.Nevertheless there is no sort of justification for attempting to separate milk into classes, which are not broad enough to include the variations which have been repeatedly shown, although not always on sound lines, to occur in the figures. It may be possible so to separate milk of very low bacterial content, but it is not possible to do so when the bacterial content exceeds, say, 200,000 per 1 c.c. It must always be remembered that the colonies appearing on agar plates arise from groups as well as from individual bacteria.In view of the fact that keeping quality, the basis on which the consumer judges milk, depends upon the kinds as well as upon the numbers of bacteria, it appears wise to supplement bacterial examinations with determinations of keeping quality, and, in view of their special significance, of organisms of the coliform group.It seems that, although the methods of Breed and Frost are excellent for rapidly classifying milk into broad grades, their accuracy is necessarily diminished by their very nature, in that the results obtained are dependent upon computation to a greater extent than the plate method and, although it is possible to secure good results, the time consumed in getting these is as great, if not indeed greater, than by the plate method.The reductase test, although it has a large sphere of usefulness as a factory method, will not give accurate information as to the numbers of bacteria in milk.

scholarly journals Growth and enterotoxin production of Bacillus cereus in cow, goat, and sheep milk

2014 ◽  
Vol 83 (10) ◽  
pp. S3-S8 ◽  
Author(s):  
Lenka Necidová ◽  
Šárka Bursová ◽  
Alena Skočková ◽  
Bohdana Janštová ◽  
Pavla Prachařová ◽  
...  
Keyword(s):  
Bacillus Cereus ◽  
Storage Temperature ◽  
Goat Milk ◽  
Storage Conditions ◽  
Cow Milk ◽  
Enzyme Linked Immunosorbent Assay ◽  
Plate Method ◽  
Milk Samples ◽  
Sheep Milk ◽  
Enterotoxin Production

The aim of this study was to compare Bacillus cereus growth rates and diarrhoeal enterotoxin production in raw and pasteurized goat, sheep, and cow milk in terms of storage conditions. Milk samples were inoculated with B. cereus (CCM 2010), which produces diarrhoeal enterotoxins. Enterotoxin production was tested by ELISA (Enzyme-Linked Immunosorbent Assay), and the count of B. cereus was determined by the plate method. With raw cow milk, B. cereus growth and enterotoxin production can be completely suppressed; in raw goat and sheep milk, enterotoxin was produced at 22 °C. In pasteurized cow, goat, and sheep milk, the B. cereus count increased under all storage conditions, with more rapid growth being observed at 15 °C (sheep milk) and 22 °C (cow and goat milk). Enterotoxin presence was detected at 15 °C and 22 °C, and with pasteurized cow milk also at 8 °C. Our model experiments have determined that B. cereus multiplication and subsequent enterotoxin production depend on storage temperature and milk type.

Determination of Viable Bacterial Populations in Raw Milk within 20 Minutes by Using a Direct Epifluorescent Filter Technique

1997 ◽  
Vol 60 (7) ◽  
pp. 874-876 ◽  
Author(s):  
CLAUDE P. CHAMPAGNE ◽  
NANCY J. GARDNER ◽  
JULIE FONTAINE ◽  
JACQUES RICHARD
Keyword(s):  
Raw Milk ◽  
Plate Count ◽  
Bacterial Populations ◽  
Filter Technique ◽  
Milk Samples ◽  
Standard Plate ◽  
Plate Counts ◽  
Direct Epifluorescent Filter Technique ◽  
Triton X

The results from a shortened procedure for the direct epifluorescent filter technique (DEFT) determination of viable bacterial populations in raw milk were compared to standard plate counts. Shortening the prefiltration trypsin-Triton X-100 incubation period from 10 to 3 min enabled the completion of the analysis within 20 min. The short DEFT method results had a correlation coefficient (r) of 0.81 with plate counts. With respect to precision, the average difference between values of duplicate plate count analyses was 0.16 log units; that of the short DEFT was 0.14 log units. The slopes of the regressions equations were less than 1, indicating that a direct correlation is not achieved. Short DEFT values were 0.17 log units higher than those of plate counts on milk samples containing less than 10,000 CFU/ml. For milk samples containing counts over 10,000 CFU/ml, short DEFT values averaged only 0.05 log units above plate count readings. Daily preparation of the stain appears unnecessary since acridine orange solutions stored for up to 2 days at 4°C did not produce results significantly (P > 0.05) different from those obtained with fresh solutions. The short DEFT method has potential for the assessment of the bacteriological quality of raw milk in tanker deliveries.

Rapid Detection of Psychrotrophic Bacteria In Manufacturing Grade Raw Milks

1991 ◽  
Vol 54 (11) ◽  
pp. 861-867 ◽  
Author(s):  
S. R. TATINI ◽  
P. MEKALA ◽  
A. EL-HABAZ ◽  
M. W. GRIFFITHS
Keyword(s):  
Rapid Detection ◽  
Bacterial Count ◽  
Raw Milk ◽  
Plate Count ◽  
Psychrotrophic Bacteria ◽  
Milk Samples ◽  
Microscopic Count ◽  
Direct Epifluorescent Filter Technique ◽  
Native Microflora

Methods to rapidly assess the bacteriological quality of raw milk were investigated. Whereas direct microscopic count, modified psychrotrophic plate count, and direct epifluorescent filter technique (DEFT) did not correlate well with initial psychrotrophic bacterial count of raw milk, improvements were obtained after preincubation of the milk samples. The best preincubation conditions were identified as 30°C for 6 h, 21°C for 10 h, 13°C for 15 h, 13°C for 20 h, or 7°C for 37 h. The “square root” equation was applied to the data, and a model was produced for predicting growth of the native microflora of raw milk. Using this equation, a DEFT count after preincubation of the milk at 21°C for 10 h could accurately predict the initial psychrotroph count and the count after storage of the milk at 6°C for 48 h.

Evaluation of an 18°C/45-Hour Plate Count Technique for the Enumeration of Psychrotrophic Bacteria in Raw and Pasteurized Milk

1983 ◽  
Vol 46 (6) ◽  
pp. 528-529 ◽  
Author(s):  
HARRY K. OEHLRICH ◽  
ROBIN C. MCKELLAR
Keyword(s):  
Plate Count ◽  
Reliable Estimate ◽  
Additional Test ◽  
Bacterial Counts ◽  
Pasteurized Milk ◽  
Psychrotrophic Bacteria ◽  
Milk Samples

Bacterial counts were done at 7°C for 10 d and at 18°C for 45 h on 93 samples of raw and 185 samples of pasteurized milk. As an additional test, catalase-positive microorganisms were enumerated at 18°C/45 h. Close correlations were obtained between the numbers of microorganisms following 18°C/45-h and 7°C/10-d incubations in raw (r2=0.866) and pasteurized (r2=0.936) milk samples. Similar correlations (r2=0.860 and 0.946) were noted for the 18°C/45-h-catalase and the 7°C/10-d methods for raw and pasteurized milk, respectively. Results suggest that incubation at 18°C for 45 h provides a reliable estimate of the numbers of psychrotrophs in raw and pasteurized milk and that the use of catalase does not improve sensitivity of the test significantly.

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.

Molecular Analysis of Spoilage-Related Bacteria in Pasteurized Milk during Refrigeration by PCR and Denaturing Gradient Gel Electrophoresis

2009 ◽  
Vol 72 (3) ◽  
pp. 572-577 ◽  
Author(s):  
HONGFEI HE ◽  
JIN DONG ◽  
CHIN NYEAN LEE ◽  
YONG LI
Keyword(s):  
Shelf Life ◽  
Gel Electrophoresis ◽  
Denaturing Gradient Gel Electrophoresis ◽  
Plate Count ◽  
Pasteurized Milk ◽  
Milk Samples ◽  
Gradient Gel Electrophoresis ◽  
Aerobic Plate Count ◽  
Species Specific

Bacterial diversity in fluid milk products has been extensively studied in order to improve milk quality. Here, we illustrate the utility of viable counts and PCR–denaturing gradient gel electrophoresis (DGGE) for monitoring the microbial spoilage of pasteurized milk during shelf life. Five pasteurized milk samples stored at 4°C were examined at 10 and 5 days before expiration and on the expiration day. With bacterial DNA extracted directly from the samples, PCR-DGGE analysis indicated that Pseudomonas became dominant in four samples. Meanwhile, the aerobic plate count of these four samples exceeded the regulatory limit of 20,000 CFU/ml at 5 days before expiration, and the rapid psychrotrophic count markedly surpassed the aerobic plate count on the expiration day. Streptococcus and Buttiauxella spp. were detected in several samples. Sequence analysis of DGGE fragments revealed high diversity among Pseudomonas spp. in the milk samples. P. putida and P. migulae grew to high numbers during refrigerated storage. Further identification of Pseudomonas at the species level was facilitated by PCR and multiplex PCR using species-specific primers; consequently, P. fluorescens and P. fragi were observed. These results highlight an important role of Pseudomonas in the shelf life of pasteurized milk.

Use of Fast Green FCF with Tryptic Soy Agar for Aerobic Plate Count by the Hydrophobic Grid Membrane Filter

1986 ◽  
Vol 49 (4) ◽  
pp. 278-279 ◽  
Author(s):  
PHYLLIS ENTIS ◽  
PETER BOLESZCZUK
Keyword(s):  
Membrane Filter ◽  
Food Samples ◽  
T Test ◽  
Plate Count ◽  
Paired Data ◽  
Plate Method ◽  
Fast Green ◽  
Product Categories ◽  
Aerobic Plate Count ◽  
Fast Green Fcf

A hydrophobic grid membrane filter (HGMF) method for aerobic plate count using Tryptic Soy Agar with fast green FCF was evaluated against a conventional pour plate method on 250 food samples, representing 25 product categories. The HGMF method yielded counts equivalent to or significantly higher than the pour plate method for 24 of the 25 product categories (t-test for paired data).

A Practical Evaluation of the Delvotest P Multi Plate Test in Screening Raw Milk for Antibiotics

1986 ◽  
Vol 49 (11) ◽  
pp. 868-870 ◽  
Author(s):  
LYSE LAROCQUE ◽  
G. A. NEVILLE
Keyword(s):  
Bacillus Subtilis ◽  
Staphylococcus Epidermidis ◽  
Raw Milk ◽  
The Other ◽  
Penicillin G ◽  
Antibiotic Residues ◽  
Plate Test ◽  
Milk Samples ◽  
Practical Evaluation ◽  
Bacillus Subtilis Atcc

The Delvotest P Multi plate test was evaluated by screening 100 milk samples for total antibiotic residues (penicillin G, streptomycin and neomycin). The samples were taken in conjunction with an antibiotic depletion study in milk derived from six cows treated with a multiple antibiotic, intramammary infusion product. Within the limits of sensitivity of the Delvotest, only penicillin G persisted in milk samples taken beyond 60 h, whereas in some samples, the other antibiotics appeared to be depleted as early as 48 h. More sensitive tests, however, detected neomycin (Staphylococcus epidermidis, ATCC 12228) in 50% of samples taken at 60 h and streptomycin (Bacillus subtilis, ATCC 6633) at 14.5 d after discontinuation of infusion.

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