THE USE OF INHIBITORY MEDIA TO SCREEN SOUTH DAKOTA BULK TANK MILK FOR STREPTOCOCCUS AGALACTIAE

Abstract

Edward's medium with red blood cells, staphylococcus beta toxin, and ferric citrate (TKT medium) was used to culture 4189 bulk tank milk samples from herds supplying seven dairy plants in South Dakota. Identity of organisms with characteristics of Streptococcus agalactiae on TKT was tested by biochemical means. The incidence of S. agalactiae infected herds supplying the seven milk plants ranged from 0% to 66.6% and averaged 4.03%. Difficulty was encountered in identifying S. agalactiae by its characteristics on TKT alone so that only about one out of ten colonies picked as S. agalactiae from TKT had all the characteristics of this organism. Some limitation of the method for use in S. agalactiae eradication is thus indicated. Modified KF Agar was found unsuitable for the direct isolation and identification of S. agalactiae from bulk tank milk.