Phenotypic and Genotypic Characterization of the Virulence Factors and Antimicrobial Resistance of Enterobacteriaceae Isolates Associated with Clinical Mastitis in Dairy Cattle

Mastitis is a prevalent disease in dairy cattle. One of its important etiological agents is the species belonging to the Enterobacteriaceae family. Thus, this study aims to characterize the virulence and multi-drug resistance (MDR) profiles of Enterobacteriaceae strains previously isolated from dairy cattle with clinical mastitis in Region 4-A, Philippines. Results showed that 60% of Klebsiella pneumoniae and 100% of the Proteeae tribe (Proteus spp., Providencia spp., and Morganella spp.) exhibited hemolytic activity. Hemolysin-coding gene, viz. hpmA, was suspected to contribute to the hemolytic activity of all Proteus spp. Biofilm formation was observed in several isolates and mrkD, ireA, ucaA, atfA, and ureG genes were expected to be accountable for this virulence trait. All Enterobacteriaceae strains were classified as MDR pathogens. All isolates exhibited resistance to erythromycin, penicillin, clindamycin, and lincomycin. Resistance to streptomycin and tetracycline was also exhibited by a significant number of isolates and the resistance genes (rrs and tetK) responsible for this resistance were most frequently detected. Only one isolate of M. morganii harbored integron-related gene intI2. The characterization of these strains has significant health and economic implications. Severe virulence and drug resistance of these strains pose a challenge in the management and treatment of intramammary infections in dairy farms. Being reservoirs of antimicrobial resistance-associated genes, these strains pose a threat to the food chain.