Isolation and Characterization of Staphylococcus spp. and the Unintended Discovery of Non-Staphylococcal Strains Associated with Bovine Mastitis in Region IV-A, Philippines

Abstract

Bovine mastitis is a common bacterial infection that causes inflammation of the mammary gland in dairy cattle. Staphylococcus is one of the most predominant and significant pathogens known to cause mastitis. Thus, this study was designed to isolate and assess the prevalence of Staphylococcus strains in dairy cattle with clinical mastitis in Region IV-A, Philippines. Baird Parker agar (BPA) supplemented with 5% egg yolk tellurite emulsion was used as selective media to differentiate coagulase-positive S. aureus and coagulase-negative staphylococcus (CNS). The isolated pathogens were phenotypically and genetically characterized for further identification. Surprisingly, out of 85 isolates, only 56.5% belong to the genus Staphylococcus and 43.5% were non-staphylococcus strains despite the use of a staphylococcus-specific selective medium. The overall most prevalent species among the isolates were S. chromogenes with an isolation rate of 21.2%. The antimicrobial resistance profiles of the isolated bacterial pathogens were also done. Several staphylococcal isolates exhibited resistance to multiple antibiotics. S. aureus showed hyper-resistance to three out of seven antibiotics – specifically streptomycin, clindamycin, and lincomycin. Surprisingly, most of the non-staphylococcal isolates exhibited hyper-resistance to multiple antibiotics. Proteus mirabilis, P. penneri, and Providencia stuartii showed almost 100% resistance and hyper-resistance to all antimicrobials tested except amoxicillin. These findings suggest that the detection of diverse species of mastitis-causing microorganisms is an important concern for the dairy sector, as different pathogens might represent different hazards and require distinct treatments, particularly on the type of antibiotics used to treat the infection. The erroneous choice of antimicrobial could unnecessarily expose the udder microbial flora to antimicrobials, thereby inadvertently promoting the emergence of multidrug-resistant pathogens that poses a serious threat to both animal and human health. Extreme antibiotic resistance detected in strains present in mastitic dairy cattle also raises a substantial public health concern, particularly when it comes to the consumption of food and food products, such as milk.