The problem of Staphylococcus aureus contamination in Buffaloe Dairy Farms
By
Nashwa, O. Khalifa, ** Nahla, A. Abou-El Roos and *** Eman, M. Sharaf
* Dept. of Zoonoses, Fac. Vet. Med. Benha Univ., ** Dept. of Food Technology and Control, *** Dept. of Bacteriology, Animal Health Research Institute, Dokki, Giza, Egypt.
Summary
The small scale production of raw milk products are usually produced in some buffaloe dairy farms in absence of sanitary govern measures and under a low hygienic condition and may constitute a risk of Staphylococcus food poisoning to consumers. This study aimed to determine the sources of contamination with coagulase positive Staphylococcus aureus in some buffaloes dairy farms with small scale production of raw milk soft cheese. Samples were collected from raw milk, raw milk soft cheese and swabs from palm of hands of milkers (30 of each). The bacteriological examination of the collected samples revealed that typical colonies of Staphylococcus aureus on Baird Parker agar were identified in 5 (16.66%) raw milk, 7 (23.33%) raw milk soft cheese and 8 samples of palm of hands of milkers (26.66%). All identified Staphylococcus aureus samples were coagulase positive and presented a 2+ or more for coagulase reaction. The presence of coagulase positive Staphylococcus aureus in raw milk and raw milk soft cheese is an indication of contamination and low hygienic measures in the farms under investigation. The public health importance of that germ and suggested control measures to prevent contamination were discussed.
Introduction
Staphylococcal food poisoning caused by milk and milk products involving large numbers of people throughout the world have been attributed to Staphylococcus aureus (11). The method of choice for isolation of Staphylococcus aureus in most dairy products is the Baird-Parker plate method (13). The characteristic of Staphylococcus aureus on Baird-Parker agar and the result of coagulase are critical factors for the proper isolation, identification and enumeration of the organism in milk and other dairy products (20). Staphylococcus aureus strains that produce enterotoxins are coagulase positive and very few coagulase negative strains are enteotoxigenic. The enterotoxins are resistant to hydrolysis by gastric and jejunal enzymes and can withstand heating at 100ºC for 30 minutes and cause food –poisoning in human. The principal reservoir of Staphylococcal food poisoning is the human carrier expelled the organism from the respiratory tract during sneezing or coughing or the human with skin lesion in the hand who preparing food (1). After the Staphylococcus have introduced into the food, the food remain at room temperature or warmer to permit the growth of the organism and release the toxins. Subsequent heating of the food will kill the bacteria but not inactivate the heat-stable toxins. Furthermore, the contaminated foods have no pronounced changes in the odour or taste (16). Dairy cows with mastitis are also reservoirs of the infection and infected milk with Staphylococci can contaminate numerous milk products (7). In developing countries where refrigeration after milking is often inadequate, milk and milk products may be an important source of staphylococcal intoxication (1).
This study aimed to throw spotlight on the problem of coagulase positive Staphylococcus aureus contamination in buffaloe dairy farms with small-scale production of raw milk soft cheese.
Materials and Methods
Sampling :
In the present work the samples were randomly collected from some buffaloe dairy farms with small scale- production of raw milk soft cheese in different localities in Kaliobia governorate. About 10 ml of raw milk and 10gm of raw milk soft cheese (30 samples of each) were collected under aseptic condition. As well swabs were taken from palm of hands of 30 apparently healthy milkers for bacteriological examination. The collected samples were labeled and kept in containers with ice packs and transferred to the laboratory without delay. The sampling technique was performed after (20).
Isolation and Identification of Staphylococcus aureus :
The collected samples were dipped into 10 ml of sterile peptone water and aliquots of 0.1ml were surface plated on Baird. Parker agar (Oxoid) and incubated at 37ºC for 48 hours (3). Colonies of typical growth were gray to black surrounded by faint yellow zone were picked up and streaked onto brain heart infusion slants and incubated overnight at 37ºC. Each isolate was subjected to Gram stain and biochemically tested for production of catalase, H2S, mannitol fermentation, hemolysis on blood agar, pigmentation and gelatin liquefaction according to (4, 12). All the positive isolates were submitted to coagluase test for confirmation of Staphylococcus aureus as described by (15).
Results and Discussion
A total of 90 samples from raw milk, raw milk soft cheese and palm of hands of milkers were screened for the presence of coagulase positive Staphylococcus aureus (table1). The results proved that typical morphology of Staphylococcus aureus was identified in 5 sample of raw milk (16.66 %), 7 sample of raw milk soft cheese (23.33%) and 8 sample of palm of hands of milkers (26.66%). Typical colonies of Staphylococcus aureus on Baird-Parker agar are with an opaque halo surrounded by zone of clearing zone is due to proteolytic action (7). Our results were in accordance with those reported by (20, 19, 8), but lower than those recovered from raw milk by (9, 10).
Table (2) declared that all typical colonies of Staphylococcus aureus on Baird-Barker agar were positive to additional diagnostic features including microscopical examination by Gram staining and biochemical identification including catalase test, H2S, mannitol fermentation, hemolysis on blood agar, pigmentation on nutrient agar and gelatin liquefaction. A finding was similar to those examined by (4, 12).
The identified Staphylococcus aureus were further subjected to coagulase test. Table (3) pointed out that all Staphylococcus aureus isolated from raw milk, raw milk soft cheese and palm of hands of milkers were coagulase positive and all strains presented a 2+ or more for coagulase reaction. Similarly (12) reported that all strains isolated from milk were coagulase positive.
In Egypt the available literatures revealed that some researchers have isolated Staphylococcus aureus from pickled domiati chees, white soft cheese and raw milk by (14, 5,2) respectively.
Many outbreaks of food poisoning have been produced by consumption of inadequately refrigerated raw milk or cheese from cows whose udder harbored Staphylococci (1). The largest outbreak affected at least 500 students in California between 1977 and 1981 and was traced to chocolate milk (6). The incubation period is short, generally 3 hours after ingestion of the food involved. The major symptoms are nausea, vomiting, abdominal pain and diarrhea (7). Staphylococcus aureus is well adapted to survive in the udder and usually establishes a mild subclinical infection over a long duration and are shed in the milk, which serves as a source of infection for the healthy bovine (18).
Furthermore, the unhygienic conditions in which those dairy products are manufactured and water used for washing of utensils have accelerated the bacterial contamination of milk and milk products (19). Premilking udder hygiene is a vital component of a total milk quality program and may reduced the bacterial content in milk and their presence on teats. On the other hand, improper udder preparation prior to milking may increase the number of Staphylococci in milk (17).
In conclusion, the present study showed that Staphylococcus aureus could be recovered from raw milk, raw milk soft cheese and palm of hands of milkers which may be attributed to neglected hygienic measures adopted during milking, handling and processing of soft cheese. Thus more strict hygienic and preventive measures are required to reduce the bacterial contamination of milk and milk products.
Table(1): Results of morphological characters of Staphylococcus aureus on Baid-Parker agar.
Sample Number of sample collceted Typical colonies
Number Percent
Raw milk 30 5 16.66
Raw milk soft cheese 30 7 23.33
Palm of hands of milkers 30 8 26. 66
Total 90 20 22.22
Table(2): Results of identification of Staphylococcus aureus.
Sample Number of sample collected Number of positive isolates Microscopical identification Biochemical
*identification
Raw milk 30 5 +ve +ve
Raw milk soft cheese 30 7 +ve +ve
Palm of hands of milkers 30 8 +ve +ve
Total 90 20 +ve +ve
* Catalase, H2S, mannitol fermentation, hemolysis on blood agar, pigmentation and gelatin liquefaction
Table (3): Occurrence of coagulase positive Staphylococcus aureus in buffaloe dairy farms
Sample Number of sample collected Coagulase positive isolates
(++) or more
Number Percent
Raw milk 30 5 16.66
Raw milk soft cheese 30 7 23.33
Palm of hands of milkers 30 8 26. 66
Total 90 20 22.22
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مشكلة التلوث بالميكروب العنقودي الذهبي في مزارع الألبان الجاموسى
* نشوه عثمان خليفة ** نهلة أحمد ابو الروس ** وإيمان محمود شرف
* قسم الأمراض المشتركة بكلية الطب البيطرى – جامعة بنها ، ** قسم مراقبة الأغذية ،
*** قسم البكتريولوجي – معهد بحوث صحة الحيوان بالدقى
تمثل منتجات الألبان الغير معاملة بالحرارة أثناء التصنيع خطراً علي صحة الإنسان فهي عادة ما تصنع علي نطاق صغير داخل بعض المزارع وفي غياب من الرقابة الصحية وتحت ظروف صحية سيئة مما يجعلها مصدراً خطيراً من مصادر العدوي بالتسمم الغذائى بالميكروب العنقودي الذهبي وتمثل مشكلة للصحة العامة. وقد أجريت هذه الدراسة للكشف عن مشكلة التلوث بالميكروب العنقودي الذهبي في بعض مزارع الجاموس الحلابة بمحافظة القليوبية. وقد تم جمع عينات من اللبن الخام والجبن الطرى المصنع من اللبن الخام ومن أيدي الحلابين وأجريت التجارب المعملية اللازمة لعزل الميكروب وتصنيفه وكانت نسبة عزل الميكروب 5 عينات بنسبة (16.66%) ، 7 عينات بنسبة (23.33%) ، 8 عينات بنسبة (26.66%) في كل من عينات اللبن الخام والجبن الطرى المصنع من اللبن الخام وأيدي الحلابين علي التوالي. هذا ويعتبر وجود الميكروب العنقودي الذهبي في الألبان ومنتجاتها مؤشر للتلوث داخل هذه المزارع أثناء الحليب أو التصنيع أو استخدام الأدوات الملوثة . وتم مناقشة الأهمية الصحية للميكروب والطرق المقترحة لتفادي التلوث به .
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