[Federal investigations on the distribution and in vitro resistance of udder pathogenic bacteria in the milk of cows with subclinical mastitis].

1644 quarter milk samples of 948 dairy cows with subclinical mastitis, collected from 63 veterinary practices all over Germany origined by 262 livestocks with problems in udder health were examined semiquantitatively by "Aulendorfer Mastitistest" for cell count and additionally bacteriologically. Potentially udder pathogenic bacteria were tested for in vitro-sensitivity to penicillin G, ampicillin, oxacillin, cefacetril, tylosin, neomycin, gentamicin, polymyxin B and enrofloxacin. 24.5% of all tested milk samples were bacteriologically negative. In 35.3% of the bacteriological positive milk samples Staphylococcus (S) aureus was detected. Enterococci, Streptococcus (Sc.) uberis, Sc. dysgalactiae and Sc. agalactiae were found in 8.9%, 8.2%, 8.1% and 4.9% of all positive milk samples, respectively. G-streptococci were found only occasionally. Apathogenic bacteria like coagulase-negative staphylococci, micrococci, aerobic bacilli and coryneforms were detected in 45.0% of all positive milk samples. Enterobacteriaceae (E. coli, klebsiella spp., proteus spp. and other coliforms) were isolated in 3.3% of all cases and should be considered as insignificant for the subclinical mastitis of dairy cows in Germany. Against S. aureus cefacetril and oxacillin were mostly effective in vitro, whereas penicillin G was ineffective because 40% of these bacteria are penicillinase-positive. Streptococci and enterococci were mostly sensitive to cefacetril, oxacillin, penicillin G and ampicillin. Concerning the distribution of bacteria regional differences were recognized. Regional differences concerning in vitro-sensitivity were negligible. The results are discussed.