Characteristics of staphylococci isolated from clinical and subclinical mastitis cows in Shahrekord, Iran

Staphylococci isolated from 98 mastitic cow’s milk samples were analyzed for the production of alpha, beta and delta-hemolysin on sheep, bovine and horse red blood cells and in vitro susceptibility to several antimicrobial agents. Out of a total of 18 isolated strains, 100% demonstrated hemolytic activity either alone or in combined forms. Among 8 isolates of S. aureus 3 isolates produced α/β and 5 produced α/β/δ hemolysins. From 10 isolates of coagulase-negative staphylococci (CNS), 2 α, 2 δ, 2 α/δ and 4 α/β/δ hemolysins producing isolates were confirmed. S. aureus isolates were resistant to cloxacillin (100%), penicillin (87%) and ampicillin (62.5%). CNSs showed resistance only to amoxicillin (60%). The results suggest that a cow’s infected mammary glands are an important reservoir of hemolytic staphylococci. A high degree of S. aureus antimicrobial resistances was detected.