Abstract
Food-borne diseases are the main public health problem throughout the world. Milk is important component of human diet including fats, proteins, vitamins and minerals. It is a best source of calcium and phosphorus. Different types of pathogenic bacteria like S. aureus and Salmonella enter in milk and then multiply, after multiplication they become active in causing diseases. These bacteria create serious problems for human health. This study aimed to isolate and identify pathogenic bacteria Staphylococcus aureus and Salmonella from raw milk samples of different cities of Pakistan. Primary screening of raw milk samples was done on the basis of morphological, cultural and biochemical techniques. The final identification was made using 16SrRNA sequence analysis. A total of 200 raw milk samples were collected from different cities of Pakistan. Selective medium xylose lysine deoxycholate agar (XLD) and Mannitol salt agar were used for the identification of Salmonella sp. and S. aureus. Staphylococcus aureus produced yellow colonies with yellow zones on Mannitol salt agar. Staphylococcus aureus exhibited gram-positive character with purple coloration and it was detected as cocci-shaped. Biochemically 91 (45%) samples enhibited Catalase, Coagulase, DNase, Urease, Citrate, fermentation tests positive and indole, oxidase and H2S tests negative with nonmotile character, indicating the presence of Staphylococcus aureus. Salmonella sp. was detected as gram negative rods with pink coloration on gram staining. Biochemically 87 (43%) samples revealed catalase, citrate, H2S and fermentation tests positive while oxidase, DNase, Indole and urease tests negative, indicating the presence of Salmonella sp. in these samples. Of the 200 samples tested, 43% were positive for Salmonella, while 45% samples were contaminated with S. aureus. The 16SrRNA sequence analysis confirmed the results of biochemical and cultural characterization by depicting 99% identity of samples with S. aureus and 98% identity with Salmonella spp. The occurrence of high percentage of these pathogenic bacteria in raw milk may be linked to its contamination at the time of collection, processing, strorage and distribution. This quantitative data could be utilized to better establish the appropriate levels of protection for raw milk, dairy products and processing technologies.
Highlights
Milk is complex ecosystem for various microorganisms as well it is essential component of diet or best medium for bacterial growth
S. aureus is mostly present in unpasteurized milk and such contaminated milk products cause food poisoning and gastrointestinal illness, which are responsible for broad variation in texture and taste of milk and produce enzymes which can facilitate bacterial attack and proliferation in the body of host
S. aureus was detected in 45% samples of raw milk collected from different cities of Pakistan while 43% samples of raw milk were positive for Salmonella sp. (Figure 1)
Summary
Milk is complex ecosystem for various microorganisms as well it is essential component of diet or best medium for bacterial growth. Food borne infection has been increasing day by day due to different types of food contaminating bacteria [10] These diseases are among the main public health problems throughout world. Different types of pathogenic bacteria were detected in a study of Malyer city in Iran They had indicated the presence of E. coli (75%), S. aureus (52%), Klebsiellia (36%), proteus (4%) in raw milk. S aureus is a most important food born pathogenic organism causing usually skin infections as well as other diseases like boils, cellulite, toxic shock syndrome [15]. Present study was designed to isolate pathogenic bacteria (Salmonella spp. and S. aureus) from unpasteurized milk of different cities of Pakistan. This may help to control the outbreak of harmful diseases due to raw milk and it’s products consumption
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