Occurrence of Mastitis in Dairy Herds and the Detection of Virulence Factors in Staphylococci

Abstract

Mastitis is still a major challenge that affects milk quality. The study is aimed to examine the health of the mammary gland and identify the udder pathogens and virulence factors that caused mastitis in 960 dairy cows and 940 ewes, respectively. We found that Staphylococci and streptococci are the most common causes of mastitis in those dairy animals. Coagulase-negative staphylococci (CoNS), along with the main udder pathogens such as S. aureus, S. uberis, and S. agalactiae, are a major concern for dairy animals. The majority of the virulence factors (production of hemolysis, gelatinase, biofilm, ability to hydrolyze DNA, and antibiotic resistance) were found in S. chromogens, S. warneri, and S. xylosus isolates from clinical and chronic cases of mastitis. S. aureus and CoNS strains tested by disk diffusion showed 77.0 and 44.2% resistance to one or more antimicrobial classes in mastitic milk samples from dairy cows and ewes, respectively. The presence of a methicillin-resistant gene mecA poses serious complications for treatment and indicates a health risk to milk consumers due to the resistance to β-lactam-antibiotics in two isolates of S. aureus and two species of CoNS isolated from cows’ mastitic milk samples.