Relationship between incidence of probiotics and presence of pathogenic bacteria in milk products

Abstract

Milk and dairy products hold a prominent place in the Egyptian diet; however, their contamination by pathogenic microorganisms constitutes a significant public health concern. Bacterial contamination of fermented dairy items is particularly critical, as it compromises both the safety of the end products and facilitates the transmission of foodborne pathogens to the population. Therefore, this study was conducted for the investigation of the incidence of probiotic and potentially pathogenic bacteria in dairy products with a focus on the relationship between the presence of probiotic and pathogenic microorganisms. Ninety samples, including Rayeb, yogurt, and cheese, were analyzed. The samples were collected randomly from different localities in Assiut city, Egypt. All microorganisms were isolated in corresponding media, and the resulting colonies were purified through repeated subculture. They were preliminarily identified based on Gram staining, morphology, and biochemical tests. Molecular identification was then performed using PCR. The results obtained showed that the occurrence of Lactobacillus, Bifidobacteria, Enterococcus, Salmonella, E. coli and S. aureus was 46.7%, 33.3%, 30%, 05, 0% and 46.7% for Rayeb, 13.3%, 20%, 33.3%, 10%, 0 % and 26.7% for yogurt and 26.7%, 0%, 6.66%, 30%, 20% and 70% for Karish cheese. PCR screening revealed that Rayeb contained 66.67, 0, 0, 0, 0 and 37.5, and yogurt contains 36.36, 0, 0, 0, 0 and 0, and Karish cheese 54.54, 0, 9.5, 22.22, 83.33, and 0 for Lactobacillus, Bifidobacteria, MRSA, Salmonella, E. coli, and Enterococcus, respectively. Two representative lactic acid-containing samples from each product were sequenced, and sequencing revealed the presence of  Enterococcus faecium strain R21 with accession number (PX661676) and Lactobacillus plantarum SN13T with accession number (PX661677) from Rayeb, Bacillus cereus Y3 with accession number (PX661678), and Bacillus manliponensis Y11 with accession number (PX661679) from yogurt, and Weissella viridescens K6 (PX661680) and Metabacillus halosaccharovorans K7 with accession number (PX661681).