Microbial Quality Analysis of Raw and Pasteurized Milk Samples Collected from the Southern Districts of Tamil Nadu, India

Abstract

Aims: This study aimed to evaluate the microbial quality of raw and pasteurized milk samples collected from the southern districts of Tamil Nadu. Study Design:  Cross-sectional study. Place and Duration of Study: Raw and pasteurized milk samples were randomly collected from various sources of the Thoothukudi and Tenkasi districts of Tamil Nadu between April 2024- July 2025. Methodology: From the Thoothukudi and Tenkasi districts of Tamil Nadu, 50 samples of raw (25 from each district) and pasteurized (25 from each district) milk samples (100 mL) were collected hygienically and evaluated for the Standard Plate Count (SPC) using the pour plate method. Further Isolation and Identification of E. coli was performed as per the ISO 16654 method by enrichment in Buffered Peptone Water (BPW), followed by streaking in Eosin Methylene Blue (EMB) agar, then the presumptive isolates were confirmed using biochemical assays and molecular PCR targeting the udiA gene. Similarly, Salmonella spp. were isolated as per the ISO 6579 by enrichment in Tetrathionate broth, followed by streaking in Hektoen Enteric (HE) agar, then the presumptive isolates were confirmed biochemically and molecularly by PCR targeting the Salmonella genus-specific InvA gene. Results: SPC obtained for the pasteurized milk samples were within the range of 103 to 106/mL, but most samples fell within the 104 range. Raw milk samples had higher SPC levels, ranging from 104 to 107/mL. Additionally, E. coli was isolated from 7 (28%) raw and 1 (4%) pasteurized samples, while Salmonella spp. was isolated from 4 (16%) raw samples. However, none of the pasteurized samples were positive for Salmonella spp. Conclusion: The results obtained clearly indicated the importance of hygienic milk production and pasteurization in preventing the milk-borne zoonotic threats to humans.