REPRODUCIBILITY OF ANTIBIOGRAM OF BOVINE MAMMARY-GLAND STAPHYLOCOCCI UNDER CONDITIONS OF REPEATED SUBCULTURING

The reproducibility of antibiogram profiles of 10 staphylococcal isola tes of bovine mammary gland origin was tested under conditions of repe ated subculturing. Prototype (original or index) antibiogram profiles mere determined by subculturing these isolates from stock cultures sto red at -70 degrees C. The isolates were then subcultured four times on blood agar and antibiogram profiles determined at each subculture on Mueller-Hinton agar. The antibiogram profiles of each solate at each s ubculture were compared with the prototype profiles of chat isolate. A t repeat antibiogram determinations, deviations of less than or equal to 5 mm in the individual zones of inhibition of penicillin, ampicilli n and streptomycin front the prototype antibiogram profiles, resulted in a shift of only three isolates from the resistant to intermediate a nd one isolate from intermediate to resistant status of antibiotic sus ceptibility classification. It is suggested that in the interpretation of antibiogram, susceptibility classification (resistant, intermediat e, or susceptible) variations accruing from a few millimetres differen ces in the diameter of the zones of inhibition should probably be disr egarded.