Abstract
Background:
Dairy products are nutritionally rich food items that are potentially reservoirs for food pathogenic microorganisms, especially multidrug-resistant (MDR) bacteria, if produced and/or handled under poor hygienic conditions. In addition to the fear of acquiring antimicrobial resistance within the dairy production chain, bioactive peptides from milk whey are attracting attention as natural substitutes for antimicrobial agents and as potential replacements for traditional antibiotics.

Aim:
The current study attempts to isolate and describe different bacterial species from various frequently consumed products from the dairy industry and determine their antimicrobial resistance patterns. In addition, this study aimed to determine the antimicrobial activity of peptides to be fractionated from enzymatically hydrolyzed buffalo milk whey against selected MDR dairy-derived isolates.

Methods:
Dairy samples were taken from multiple sites, totaling 290 items, including yogurts, cheeses, and creams, and were then processed in aseptic conditions. Bacterial isolates were cultured and purified using the VITEK®2 Compact System and other biochemical techniques. Using the Kirby-Bauer disk diffusion technique, the antimicrobial susceptibility exhibited 15 antibiotics and a multi-antibiotic resistance (MAR) index was calculated. The 16S rRNA gene was amplified and sequenced for molecular identification and phylogenetic analysis using universal primers. The antimicrobial activities of the whey hydrolysates and peptide fractions from processed, enzymatically hydroolyzed, and fractionated buffalo milk whey were evaluated using minimum inhibitory concentration (MIC) assays.

Results:
From the dairy products recovered, 12 species were represented by 136 bacterial isolates, with approximately equal levels across cheeses, creams, and yogurts. Significant MAR indices, with most isolates showing >0.2, indicated that many of the isolates came from environments of high contamination risk, showing resistance to tetracycline and erythromycin, ciprofloxacin, and ampicillin. Phylogenetic analysis for all isolates confirmed the closely related genetic relationship to other strains from various parts of the world for the amplified 16S rRNA gene (approximately 1500 bp). The buffalo milk whey that had been enzymatically hydrolyzed along with some of the selected chromatographic fractions exhibited high levels of antibacterial activities against the MDR isolates, although some differences in MIC values were dependent on the specific strain.

Conclusion:
The use of biochemical and molecular methods proved to be more successful in determining the type of bacteria in dairy products and showed a high frequency of isolates resistant to multiple drugs. The whey peptides derived from buffalo milk exhibited strong antimicrobial properties against the aforementioned resistant bacteria. This highlights the peptides’ ability to be used as a natural antimicrobial to help with food safety and antimicrobial stewardship in dairy production systems.

Key words: Bacteria; Dairy products; Molecular identification; Multidrug resistance.