Effect of Staphylococcus toxins isolated from dairy cow milk on Vero cell monolayers

The effect produced on Vero cell monolayers by toxins derived from Staphylococcus strains was characterized. 210 milk samples taken from dairy cows suffering from sub-clinical mastitis were analyzed. Strains belonging to the Staphylococcus genus were isolated from 73 of these milk samples. The production of toxins was then stimulated from these strains when they were cultured in Dolman's medium. The study of cell cultures showed that 53 toxin samples induced marked and irreversible cellular changes. This is compared to 42 samples (57.5%) which were strongly cytotoxic. The remaining 11 samples were shown to be slowly cytotoxic. 16% of the total toxins did not induce cell damage and 11% of the toxins produced cellular damage that was reversible in less than 24 hrs, and were designated as cytotonic. Haemolytic actively in vitro, using sheep red blood cells, was assessed using toxins that caused alteration in the monolayers. The results indicate that 46.51% of the toxins showed beta haemolytic activity, 2.32% alpha haemolytic activity, and 51.16% showed neither alpha nor beta haemolytic activity. The later type of activity did however cause damage to cultured cells, which suggests that the causative agent could be delta toxin. This study reveals a strong predominance of beta haemolytic strains in the dairy farm studied. These strains induced in vitro cell damage, and it is possible to speculate that mammary gland tissue damage is similarly produced, which may be attributed to both beta and/or delta haemolytic toxins.