Studies on Antimicrobial Resistance and Virulence Profiling of Staphylococcus aureus Recovered from Milk and its Public Health Impact

Abstract

The aim of this study was to genetically characterize S. aureus isolates recovered from dairy cows and to detect their virulence and antibiotic resistance genes which contribute to mastitis problem in the Egyptian farms and pose public health threat. A total of 412 milk samples were collected from 103 lactating cows of which 47 were suffering from clinical mastitis and 56 were positive for California mastitis test and diagnosed as subclinically mastitic cows. To investigate S. aureus existence in those gathered milk samples from cows in dairy farms in Egypt, and disclose its antimicrobial resistance profile, and related virulence/resistance-encoding genes, conventional laboratory tests as catalase, coagulase, Mannitol fermentation, Pigment production, Haemolysis, Alkaline phosphatase, Urease and Maltose fermentation and Voges - Proskauer tests were performed. In addition, vitek2 compact system used with Gram positive (GP) identification card to provide rapid and accurate phenotypic identification for the Staphylococcus isolates. S. aureus was isolated from (188) mastitic and (224) sub-clinically mastitic milk samples with an incidence of 50% (n=94) and 17.5% (n=39) respectively. Subsequently, out of 133 positive S. aureus isolates, 69 were randomly selected and subjected to antimicrobial susceptibility testing using a vitek2 compact system whereas they were challenged with a set of 15 antibacterial agents commonly used in the medical and veterinary fields.