Bacterial Content Of Milk Research Articles

Survival of Brucella Melitensis Rev - 1 in Experimentally Contaminated and Refrigerated Camel and Goat Milk

This research work aimed to examine the survival of Brucella melitensis Rev-1 in refrigerated camel and goat milk. Fresh camel and goat milk was experimentally contaminated with different concentrations of colony forming units per ml (CFU/ml) of Brucella melitensis Rev-1 and refrigerated for different periods of time. Brucella melitensis Rev-1 was detected in the refrigerated contaminated milk by isolation in culture medium and by PCR. Brucella melitensis Rev-1 was isolated from camel milk samples refrigerated for up to 8 hours. Camel milk samples refrigerated for 24 hours were negative for bacterial isolation. Brucella melitensis Rev-1 was isolated from camel milk samples containing 65 (CFU/ml) while samples containing less than that were negative for culture. The minimum content of the bacterium to be detected by PCR in contaminated camel milk was 65 CFU/ml. The higher the bacterial content of milk the better is the isolation results and whole milk was superior to cream for isolation. Brucella melitensis Rev-1 was isolated from goat milk refrigerated for up to 72 hrs. Isolation was positive for samples containing as low as 3 CFU/ml refrigerated for 4 hrs. Brucella melitensis Rev-1 was isolated from contaminated goat milk samples containing 30 to 300 CFU/ml refrigerated for 24 and 48 hrs, respectively. Samples containing higher bacterial concentrations were positive for isolation after 72 hrs of refrigeration. PCR was positive for Brucella melitensis Rev-1-contaminated goat milk containing as low as 3 CFU/ml. These results show that both isolation and PCR are sensitive for the detection of milk contamination with Brucella melitensis Rev-1, and that Brucella melitensis Rev-1 will not survive in camel milk for more than 8 hrs. the difference found here may be attributed to the nature of milk itself.

Bacterial flora in human milk in health and disease

Backgroundthe presence of bacteria in breast milk of lactating women was described more than 30 years ago and it was assumed that the cause was contamination of specimens from the mothers’ skin and infants’ mouths (Gavin & Ostovr 1977). A recent Swedish study showed that many healthy women harbour potential pathogens in their breast milk at similar concentrations to those with mastitis (Kvist et al, 2008). New methods of DNA sequencing of bacteria will revolutionize our understanding of the bacterial content of human milk. New knowledge must either be synthesized with the old or replace it.Aimto provide a synthesis and a comparison of findings from recent empirical research on microbial content of human breast milk in healthy women and women with mastitis in order to clarify present day knowledge.Methoda synthesis of the literature regarding bacterial content of breast milk from healthy women and women with mastitis, published between 1990 and 2010. This resulted in an analysis of milk from 844 healthy women and 624 women with mastitis.Findingsseven articles reported bacterial content in breast milk from healthy women, four reported findings from women with symptoms of mastitis and one study reported on bacterial content of milk from both groups. The isolate most commonly found in women with mastitis was S. epidermis (45.5%) and in healthy women the most common bacterial isolate was CNS (77.4%). S.aureus was reported in 5.1% of women with mastitis.Conclusionsa bacterial flora appears to exist in all breast milk. It is unclear why reports of sterile breast milk occur in the literature from time to time. The results of this synthesis challenge the conventional claim, that S. aureus is the most common cause of lactational mastitis.

Removal of Hair Surrounding the Teat and Associated Bacterial Counts on Teat Skin Surface, in Milk, and Intramammary Infections

The effectiveness of monthly removal of hair surrounding teats on the reduction of teat skin surface bacteria, and the incidence of intramammary infection (IMI), was studied for 10 months in a dairy farm. A split udder design was used where hair was removed on one side, left or right, with the other side serving as a control. Controls and treatment sides were randomly applied in a systematic fashion to 218 cows. Standard milking time pre- and post-milking hygiene practices were applied to all udders during the trial. Collection of teat skin swab solutions preceded aseptic collection of milk samples, performed at monthly intervals, immediately prior to milking. Teat skin bacterial counts did not differ between control and treated teats. Incidences of IMI were similar for treatment when compared with control mammary quarters, as measured by total or by pathogen type. In a second study, the effect of hair removal on the bacterial content of milk was determined using 40 cows. Treatments and allocations were as described. Udder half milk, milk from both mammary quarters of each udder half, was combined and diverted into separate buckets. Buckets were thoroughly cleaned and sanitized between milkings. A portion of bucket milk was collected 24 h after removal of udder hair. The total milk bacterial counts, and counts of psychrotrophs and thermoduric organisms were not reduced by udder hair removal. Results do not suggest that removal of udder hair leads to an improvement in milk quality as determined by milk bacterial content in the herd studied.

Use of Pulsed Ultraviolet Laser Light for the Cold Pasteurization of Bovine Milk

Because of concerns that some potentially dangerous microorganisms may survive conventional heat pasteurization of milk and because the heat needed to sterilize milk affects marketability, the ability to efficiently cold pasteurize milk may become more desirable. In this pilot study, we investigated the use of pulsed ultraviolet (PUV) laser light to nonthermally (cold) pasteurize bovine milk. Dairy bulk tank milk was treated with UV light (248 nm) emitted from a pulsed excimer laser. The samples were then analyzed for surviving bacteria by spiral plate counting and subculturing in Trypticase soy broth. Other bulk tank milk samples were inoculated with one of eight relevant milk bacterial species before being exposed to laser light. There was no growth observed for any of the plated or subcultured samples exposed to 25 J/cm2. One bacterial isolate was then used to inoculate milk to further investigate bactericidal laser light doses. Growth was observed for samples treated with an average of 0.3 to 6.6 J/cm2 but not for those treated with 12.6 J/cm2. The results indicate that in principle, the bacterial content of milk can be adequately controlled by exposure to PUV laser light.

A COMPARISON OF THE BACTERICIDAL EFFICIENCIES OF LABORATORY HOLDER AND HTST METHODS OF MILK PASTEURIZATION AND THE KEEPING QUALITIES OF THE PROCESSED MILKS

SUMMARYThe in‐place sterilization of a laboratory‐scale HTST milk pasteurizing plant and its use for the aseptic treatment of milk samples are described. Comparisons of the effect of laboratory pasteurization by holder and HTST methods on the bacterial content of milk and its keeping quality after pasteurization have been made. Experiments using sterile milk inoculated with specific test organisms showed the HTST treatment to have a greater bactericidal effect than the holder treatment against a strain of Pediococcus but with a Streptococcus strain the reverse was true. However, pasteurization of naturally infected milks from different sources showed that, in practice, both treatments yielded similar results as indicated by the relative proportions of bacteria destroyed and the keeping qualities of representative samples incubated at 22°C after pasteurization.

The Methylene-Blue Reduction Test as a Means of Estimating the Bacterial Content of Milk, to Determine its Suitability for Pasteurization or as a Basis for Grading

The Methylene-Blue Reduction Test as a Means of Estimating the Bacterial Content of Milk, to Determine its Suitability for Pasteurization or as a Basis for Grading

The Methylene-Blue Reduction Test as a Means of Estimating the Bacterial Content of Milk, to Determine its Suitability for Pasteurization or as a Basis for Grading

The Methylene-Blue Reduction Test as a Means of Estimating the Bacterial Content of Milk, to Determine its Suitability for Pasteurization or as a Basis for Grading

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

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.

51. The Plate Method of Estimating the Bacterial Content of Milk—the Limitations of Procedure in Common Use, with Suggested Improvements

The plating method of estimating the bacterial content of milk is the most important means of determining the number of living organisms present, and is the one most frequently employed. It is well recognised, however, that accurate counts cannot be obtained by this method, since considerable errors may be involved through the difficulty of ensuring the separation of chains and clusters of organisms so that each organism is represented by a separate colony, through the inability of some classes of bacteria to grow on the medium employed, and through the fact that the presence of one group of organisms may inhibit the growth of others—particularly on crowded plates. It appears that the difficulties in obtaining uniformity of counts for duplicate tests may be increased in the case of milk because this fluid is heterogeneous in nature, and the bacterial contaminants are liable to occur not only as groups or individuals freely dispersed in the liquid but also in association with matter in suspension, especially the clusters of fat globules. Consequently the bacterial counts are likely to vary with the extent to which the clusters of fat globules are broken up or aggregated by the manipulations.

Experiments on the Pasteurisation of Milk, with reference to the Efficiency of Commercial Pasteurisation

Pasteurisation at 62.8° C. (145° F.) for 30 minutes leads to a marked reduction inthe total bacterial contentof milk, varying for different specimens from 94 to 99·8 per cent., when the process is carried out under the most exact conditions. At lower temperatures,e.g.60° C., the percentage reduction may vary widely—from 51·6 to 97·4 per cent. The percentage reduction has been found to be slightly less when the same specimens of milk are pasteurised in a large scale apparatus than when treated in small quantities under laboratory conditions, the average reduction being 91·2 per cent, in the former case and 98·4 per cent, in the latter. The reasons for this are discussed.An effectively pasteurised milk should not contain lactose-fermenting bacilli in 1 c.c, and theB. colicontent is a valuable index of the efficiency of a pasteurising process.Milk containingB. tuberculosis, when pasteurised at 62·8° C. for 30 minutes (1) in tubes in a water bath in the laboratory, and (2) on a large scale by a commercial plant, is rendered non-infective to guinea-pigs. By laboratory pasteurisation, even at 60° C. for 30 minutes, milk containing tubercle bacilli is rendered non-infective.

The Bacterial Content of Cow Feces

In estimating the importance of the different factors which have to do with the contamination of market milk, fecal contamination has sometimes been underestimated. In the past it has been assumed that 5,000,000 bacteria per gram is a fair average for the cow feces which contaminates milk. For fresh feces this average might stand. But it is the feces which has dried on the cows body at near blood heat which generally contaminates milk. When the bacterial content of this type of feces is determined it is found to contain about a billion bacteria per gram. I t is easily seen that only a slight amount of contaminating material containing a billion bacteria per gram is needed to increase the bacterial content of milk tremendously. One-tenth of one gram per quart of milk might add half a million bacteria per cubic centimeter of milk. The above facts were brought out pointedly by Dr. M. J. Prucha 1 in results read before the nineteenth annual meeting of the Society of American Bacteriologists. I t is the object of the work reported here to add further data to tha t already mentioned. The media used was standard beef extract agar of reaction about pH = 6.8. Two hundred and fifty representative colonies were taken from the plates of fresh feces and were placed in litmus milk tubes

The Comparative Value of Quantitative and Qualitative Bacteriological Methods as Applied to Milk, with Especial Consideration of the Methylene Blue Reduction Test

Summary The advantages and disadvantages of the various methods of determining the number of bacteria in milk are discussed as to their applicability to raw and pasteurized milk for the purpose of determining the past history of the milk, its future history, or for control purposes either in the milk plant or by the health officials. Original data are presented which show that the methylene blue reduction test measures with a high degree of accuracy the bacterial content of milk when applied to samples of milk, the bacterial content of which has been varied by the addition of different amounts of the same inoculum.

Note on the Plate Method for Enumeration of Bacteria

In recent years much work has been done on the bacterial content of milk, chiefly with a view to demonstrating the principal sources of contamination and at the same time collecting data to aid in the fixing of a bacterial standard for “clean” milk. On looking through the various publications one is particularly impressed by the lack of uniformity in the length of the period of incubation of gelatine and agar plates. Some observers adopt a period of only a few days while others prefer to incubate for 8–10 days before counting their plates. It does not yet seem to be generally recognised, in Britain at all events, that, if the highest figures possible are to be obtained, the incubation period must be longer than three days.

A Comparison of Practical Methods for Determining the Bacterial Content of Milk

The American Public Health Association appointed a committee in 1905 to formulate standard laboratory methods for the bacterial examination of milk, following the example set by a similar committee on water analysis. The methods of milk examination in vogue at present are so widely different in the different laboratories that results cannot be compared. These different results are due to at least four factors, viz., the medium employed, the temperature of incubation, the period of incubation, and the degree of shaking before plating. The media usually employed are agar or gelatin. There are undoubtedly some arguments in favor of the use of gelatin, but the difficulty in handling gelatin plates, especially in warm weather, and the great loss occasioned by the presence of liquefying colonies probably more than counterbalance the advantages. The addition of litmus and dextrose or lactose is a common practice. The temperature of incubation has been the subject of considerable discussion, inasmuch as some workers favor incubation at 370 C, others at 200 . Since certain bacteria multiply more rapidly at 370 than at 200 , the former temperature has been often employed, so that in many laboratories counts are made after 24 hours5 incubation at 370 . It is true, however, that at 200 a higher count can be obtained than at 370 , and this fact seems to be of sufficient importance to advocate incubation at the lower temperature. It is generally conceded that at 370 multiplication is more rapid than at 200 , so that plates can be counted at an earlier date. Finally the numbers may vary with the degree of violence used in shaking milk dilutions preparatory to plating, as has been shown recently by Rosenau and McCoy.1 The points just mentioned explain to some extent the varying