Eighty one products from 36 kinds of vitamin and mineral feed supplement were examined for microbiological contamination. In addition, 83 strains of coliform isolated from the samples were tested for the resistance to 8 kinds of antimicrobial drugs and distribution of R plasmid.
General bacteria were detected in all of sample tested. Number of total bacteria varied from less than 10 per gram of the sample to 1,400,000 per gram, and 34(42%) of 81 samples were contaminated with 100 to 1,000 bacterial cells per gram.
Isolation of coliform, which was more frequent in samples with larger number of general bacteria. was possible in 14(17.3%) out of 81 samples tested and 6(33.3%) out of 18 companies in their products.
Forty one(49.4%) out of 83 coliform isolates were fecal coliforms.
The frequency of resistant strains was the highest to sulfadimethoxine(Sa) with 92.8% and followed by streptomycin (Sm, 67.5%), tetracycline(Tc, 50.6%), kanamycin(Km, 26.5%), chloramphenicol(Cm, 18.1%) and ampicillin(Am, 15.7%). No strain was resistant to nalidixic acid(Na) and gentamicin(Gm). The resistance frequency of fecal coliform strains were higher than that of non-fecal coliform strains.
There were minimum inhibitory concentration(MIC) of 3,200μg/ml or higher in 7 strains to Am, 3 to Sm and 3 to Km, and 70 strains had MIC of 1,600μg/ml or higher to Sa while Tc had MICs from 1.6μg/ml to 400μg/ml. All strains had MICs of 6.3μg/ml or lower to Na and 3.1μg/ml or lower to Gm.
Seventy nine(95.2%) of 83 strains were resistant to one or more drugs tested. The most frequent resistance patterns were SaSm(14.5%) and Sa(14.5%) and followed by SaSmTc(12%), SaSmTcKm(8.4%), SaTc(8.4%) and SaSmKm (7.2%). A total of 19 different resistance patterns were noticed.
Thirty two(40.5%) of 79 resistant strains transferred all or a part of their resistance to Escherichia coli ML 1410.
The frequency of transferable resistance was high in Am(100%) and Cm(80%) while low in Tc(38.1%), Sa(18.2%), Sm(17.9%) and Km(4.5%).
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