Staphylococcus aureus belongs to the group of major contagious
mastitis pathogens, whereas the
coagulase-negative staphylococci (CNS) are also capable of causing opportunistic
bovine mastitis. Many of these strains are resistant to
penicillin or
ampicillin because of the long-term use of
beta-lactam antibiotics in agricultural and healthcare settings. Based on the simple and highly specific
coagulase genotyping by PCR-RFLP used for discriminating among Staph. aureus strains, the relationship between phenotypic antibiogram and the polymorphism of
coagulase gene was determined in this study. The staphylococci strains (835 Staph. aureus and 763 CNS) were isolated from 3,047 bovine mastitic milk samples from 153 dairy farms in 8 provinces from 1997 to 2004 in the Republic of Korea. Twenty-one (2.5%) Staph. aureus and 19 (2.4%) CNS strains were resistant to
methicillin [
oxacillin minimum inhibitory concentration (MIC) > or = 4 microg/mL]. The
mecA gene was also found in 13 methicillin-resistant Staph. aureus (MRSA) and 12 methicillin-resistant CNS (MRCNS) isolates with a significantly higher detection rate of the
mecA gene in MRSA with high MIC (> or = 16 microg/mL) compared with those with MIC < or = 8 microg/mL. Methicillin-resistant Staph. aureus and MRCNS were also more resistant to other
antibiotics (
ampicillin,
cephalothin,
kanamycin, and
gentamicin) than
methicillin-susceptible staphylococci. Among 10 different
coa PCR-RFLP patterns (A to J) in 706 Staph. aureus strains, the main types were A (26.9%), B (17.0%), G (10.5%), and H (15.4%), with the frequent observation of the A and H types (6 and 10 isolates) in MRSA. This study indicates that major epidemic Staph. aureus clones may be spread between different dairy farms, and the profile of
coa genotype can be applied for epidemiological investigations and control of
bovine mastitis, particularly one caused by MRSA with specific prevalent
coa types.