Occurrence and clonal relatedness of sec/tst-gene positive Staphylococcus aureus isolates of quartermilk samples of cows suffering from mastitis.

Abstract

To investigate the prevalence of sec/tst-gene positive Staphylococcus aureus in bovine mastitis and to get information about the clonal relatedness of these clinical isolates. A total of 533 Staph. aureus strains isolated from bovine mastitic quartermilk samples at 493 randomized dairy farms in Hessia, Germany, from January 1997 until June 1998 were examined for enterotoxin C (sec) gene and toxic shock syndrome toxin (tst) gene by multiplex polymerase chain reaction. Fifty-three (9.3%) of the strains were sec/tst-gene positive. Phenotypic TSST-1 production was found in all positive strains by reversed passive latex agglutination test. With DNA macrorestriction analysis, sec/tst-gene positive strains were divided into five different macrorestriction types. Type I (10 isolates) and III (40 isolates) were found to be the predominant types in terms of frequency of isolation in the investigated area. These DNA macrorestriction types differed in only two bands in the 500 and 270 bp region. Closely related Staph. aureus strains seem to be responsible for an unusual large proportion of bovine mastitis cases in geographically widely distinct locations. This is one of the first reports about the relatedness of sec/tst-gene positive Staph. aureus clinical isolates from bovine mastitis.