Frequency of alpha- and beta-haemolysin in Staphylococcus aureus of bovineand human origin - A comparison between pheno- and genotype and variation in phenotypic expression

The phenotypic expression of haemolysins and the presence of genes encoding alpha and beta-haemolysin were determined in 105 Sraphylococcus aureus iso lates from bovine mastitis, 100 isolates from the nostrils of healthy human s, and 60 isolates from septicaemia in humans. Furthermore, the possible ch ange in expression of haemolysins after subcultivation in human and bovine blood and milk was studied in selected isolates. alpha-haemolysin was expre ssed phenotypically in 39 (37%) of the bovine isolates, in 59 (59%) of the human carrier isolates, and in 40 (67%) of the isolates from septicaemia. b eta-haemolysin was expressed in 76 (72%) bovine, 11 (11%) carrier, and 8 (1 3%) septicaemia isolates. Significantly more bovine than human isolates exp ressed beta-haemolysin and significantly fewer expressed alpha-haemolysin. Genotypically, the gene encoding alpha-haemolysin was detected in all isola tes. A significant difference in the prevalence of the gene encoding P-haem olysin between the bovine (96%), human carrier (56%) and isolates from sept icaemia (57%) was found. Of the bovine isolates, 75% of those carrying the gene encoding beta-haemolysin expressed beta-haemolysin phenotypically, whe reas only 20% of the carrier isolates and 24% of the septicaemia isolates d id so. No change in expression of haemolysins could be observed after subcu ltivation of bovine isolates in human blood and milk. After 5 to 10 subcult ures in bovine blood and 1 to 4 in bovine milk, 9 of 10 human isolates orig inally phenotypically beta-haemolysin negative initiated the expression of beta-haemolysin. This study showed that a larger proportion of S. aureus of bovine origin carry the beta-haemolysin gene compared to isolates from hum ans. Furthermore, a larger number of the isolates of bovine origin carrying the beta-haemolysin gene express this gene phenotypically compared to isol ates of human origin.