MICROBIAL ASSESSMENT OF RAW AND PROCESSED MILK ALONG WITH ANTIBIOGRAM PROFILING OF SELECTED ISOLATED BACTERIAL SPECIES

Abstract

Milk and dairy products are essential reservoirs for many foodborne pathogens. The most common pathogenic bacterial species in contaminated milk are Escherichia coli and Staphylococcus aureus, which are major public health concerns. Therefore, the objective of the current study was to determine the total bacterial count and identify E. coli and S. aureus along with their antibiotic sensitivity pattern from bovine milk. 41 milk samples consisting raw (n=29) and pasteurized (n=12) were collected from several dairy farms and retail outlets in some selected regions of Dhaka and analyzed for cultural, staining, and biochemical characteristics, followed by polymerase chain reaction (PCR) targeting the 16S rRNA of E. coli and the nuc gene of S. aureus. In addition, the antimicrobial susceptibility profile of the isolates was determined by the disc diffusion method. The highest Total Viable Count (TVC) for raw milk was recorded at 7.0 log cfu/ml for retail outlets, while the lowest TVC was 6.72 log cfu/ml for dairy farms. Also, the highest coliform count (CC) (was 5.87 log cfu/ml in retail outlets compared to 5.57 log cfu/ml in dairy farms for raw milk and 3.4 log cfu/ml for pasteurized milk. Overall, 44.83% of E. coli (n=13) and 60.71% (n=17) of S. aureus were found to be positive in raw milk by PCR test, of which the prevalence was 36.36% (n=4) in dairy farms and 50% (n=9) in retail outlets for E. coli, and 54.54% (n=6) and 61.11% (n=11) for dairy farms and retail outlets respectively for S. aureus. However, this study did not detect pathogenic E. coli and S. aureus in pasteurized milk. A large number of E. coli were resistant to ampicillin (84.61%), amoxicillin (76.92%), cotrimoxazole, erythromycin, and tetracycline (61.53%); however sensitive to gentamycin (92.3%), and levofloxacin (69.23%). Though several isolates of S. aureus showed sensitivity to gentamycin (76.47%), levofloxacin (70.59%), and azithromycin (58.82%), but highly resistant to amoxicillin (88.23%), ceftriaxone (82.35%), ampicillin (76.47%), and erythromycin (52.94%). This study showed that E. coli and S. aureus are widespread in raw milk samples and may develop antibiotic resistance, which might be a public health concern.