Variation of the agr locus in Staphylococcus aureus isolates from cows with mastitis

Staphylococcus aureus isolates from mastitic cow's milk were examined for production of cr-hemolysin and protein A and their accessory gene regulator (ngr locus) was analyzed. An inverse relationship between cc-hemolysin and protein A production was found in most of the 76 isolates, suggesting that the isolates tested may be classified into group I (high alpha -hemolysin/low protein A), II (low alpha -hemolysin/high protein A), or III (low alpha -hemolysin/low protein A). The agr locus, which consists of hld, agrB, agrD, agrC, and agrA, was detected in most of the 78 isolates including two reference strains (Wood 46 and Cowan I) by polymerase chain reaction (PCR). When the PCR products for agr locus of 22 isolates from groups I and II were digested with restriction enzyme MboI, seven bands of the expected lengths were recognized in strain Wood 46, but not in the other isolates tested. Nucleotide sequence analysis of PCR products from six isolates revealed that the agr locus sequence of strain Wood 46 corresponded to that of the published sequence data, but the other five isolates from groups I and LI diverged at agrB and agrD sequences and thus the deduced amino acid sequences. These variations of agr locus in S. aureus bovine isolates differed from those reported by Ii et al. [Science 276 (1997) 2027]. (C) 2001 Elsevier Science B.V. All rights reserved.