Isolation and Identification of Pathogenic Bacteria in Pasteurized Powdered Milk Sold in Ogun, Lagos and Oyo, Southwest, Nigeria

Abstract

Study’s Novelty/Excerpt • This study provides novel insights into the bacteriological quality of powdered milk sold in Ogun, Lagos, and Oyo, Southwest Nigeria, by isolating and identifying bacterial species through 16S rRNA gene sequencing and evaluating their antibiotic resistance profiles. • The research highlights the detection of potentially harmful bacteria, including Pseudomonas aeruginosa and Bacillus cereus, indicating issues related to inadequate storage or sanitation practices in the milk supply chain. • These findings underscore the importance of rigorous microbial monitoring and improved hygiene standards to ensure the safety and extended shelf life of powdered milk products. Full Abstract Milk is a nutritious beverage enjoyed by people of all ages, but it also provides an ideal environment for the growth of various microorganisms. This study aimed to isolate and identify the bacteriological quality of powdered milk sold in Ogun, Lagos, and Oyo, Southwest Nigeria. Three samples from each of five different brands were analyzed by homogenizing 1g of each milk sample with 10ml of nutritional broth, followed by overnight incubation at 37°C. Subsequently, the bacteria were plated on nutrient agar, Mac-Conkey, and EMB, with further characterization through partial sequencing of 16S rRNA genes. The detected species were then evaluated against antibiotics including Acyclovir, Cefotaxime, Augmentin, Cefuroxime, Gentamicin, Erythromycin, Ofloxacin, Nitrofurantoin, Ciprofloxacin, Nalidixic acid, and Azithromycin. The molecular testing revealed the presence of Pseudomonas aeruginosa, Bacillus cereus, Brevibacillus agri, Lysinibacillus sphaericus, and Bacillus thuringiensis as the identified bacterial species. Pseudomonas aeruginosa exhibited sensitivity to Gentamicin and Cefuroxime, with Nitrofurantoin showing the highest sensitivity at 80.0%. Brevibacillus agri (LATC3) demonstrated sensitivity to Cefuroxime and Gentamicin, with a higher sensitivity of 55.00% to Gentamicin. Bacillus cereus (LAKG2 and LAC2) showed higher responsiveness to Ceftriaxone compared to Ofloxacin, Cefotaxime, Augmentin, Acyclovir, and Levofloxacin. These findings indicate the presence of potentially harmful organisms in the microbial populations of pasteurized milk, suggesting inadequate storage practices or insufficient sanitation of facilities and equipment post-production and packaging. Therefore, monitoring the microbial quality of pasteurized milk is essential to ensure safety and extend its shelf life.

Keywords

• bacteriological quality
• powdered milk
• antibiotic resistance
• microbial contamination