Characterization of enterotoxigenic Staphylococcus aureus strains isolatedfrom bovine mastitis in north-east Switzerland

Thirty-four strains of enterotoxin-producing Staphylococcus aureus obtained from milk samples of 34 dairy cows suffering from mastitis from 34 differe nt farms in north-east Switzerland were identified and further characterize d by pheno- and genotypic methods. This included the identification of stap hylococcal enterotoxin (SE) types, an antibiotic resistance testing, the ap praisal of hemolysis, the egg yolk reaction, the detection of the clumping factor and protein A by means of a latex agglutination, the PCR amplificati on of a S. aureus specific part of the gene encoding the 16S-23S rRNA "inte rgenic spacer" region and a species specific part of the 23S rRNA-gene, the PCR amplification of the clumping factor (clfA) gene, the X region and the IgG-binding region of the protein A (spa) gene, the coagulase (coa) gene a nd additionally a macrorestriction analysis of the chromosomal DNA. Within the 26 cultures which formed a single SE, there were 23 SEC- and three SED- formers. Eight cultures were SEAD formers. It was remarkable that 22 SEC fo rmers were also positive for TSST-1. Eighteen of the 23 SEC-formers could b e classified as being of the same phenotype. Most of the cultures of one en terotoxin type also showed a great uniformity in the size and number of rep eats of the X region as well as in the size of the IgG-binding region of pr otein A gene and in the size of the coagulase gene. Macrorestriction analys is revealed 11 PFGE patterns. These were in part only different from each o ther in a few fragments and thus displayed close clonal relations. The resu lts of the present investigation show that a broad distribution of identica l or closely related enterotoxin-producing S. aureus clones seem to contrib ute to the bovine mastitis problem in north-east Switzerland. (C) 2001 Else vier Science B.V. All rights reserved.