Toxin genes and other characteristics of Staphylococcus aureus isolates from milk of cows with mastitis

In the present study, 103 Staphylococcus aureus strains isolated from milk samples from 60 cows with mastitis from eight different farms in seven diff erent locations in one region of Germany were compared pheno- and genotypic ally and by identification of various toxins. On the basis of culture and h emolytic properties and by determination of the tube coagulase reaction, al l of the isolates could be identified as S. aureus. This could be confirmed by PCR amplification of species-specific parts of the gene encoding the 23 S rRNA. In addition, all of the S. aureus isolates harbored the genes encod ing staphylococcal coagulase and clumping factor and the genes encoding the X region and the immunoglobulin G binding region of protein A. These four genes displayed size polymorphisms. By PCR amplification, the genes for the toxins staphylococcal enterotoxin A (SEA), SEC, SED, SEG, SEI, SEJ, and TS ST-1 but not those for SEB, SEE, SEH, and the exfoliative toxins ETA and ET B could be detected. To analyze the epidemiological relationships, the isol ates were subjected to DNA fingerprinting by macrorestriction analysis of t heir chromosomal DNAs. According to the observed gene polymorphisms, the to xin patterns, and the information given by macrorestriction analysis of the isolates by pulsed-field gel electrophoresis, a limited number of clones s eemed to be responsible for the cases of bovine mastitis on the various far ms.