CHARACTERIZATION OF ANTIBIOTIC-RESISTANCE IN STREPTOCOCCUS-SUIS

Twenty one isolates of Streptococcus suis were screened for antibiotic resistance by growth on antibiotic-containing media, by measuring min imum inhibitory concentrations, by hybridization to specific DNA and o ligonucleotide probes for antibiotic resistance genes, and by PCR, The isolates were from a slaughter house survey of respiratory pathogens in Norwegian pigs in 1986. Fifteen isolates were resistant to tetracyc line, with MICs ranging from 4-128 mu g/ml. Genes coding for the Tet O and Tet M determinants were detected in eight and five isolates, resp ectively. Genes coding for other Gram positive Tet determinants, Tet K , Tet L, and Tet P, were not detected. One isolate was constitutive re sistant to erythromycin with MIC of 128 mu g/ml. Five other isolates c arried inducible erythromycin resistance. All these isolates, and five others, were positive in a PCR assay for erythromycin resistance, and hybridized with the Erm C and/or Erm B probes. No resistance against chloramphenicol (5 mu g/ml) or rifampin ( 10 mu g/ml) could be detecte d, but five isolates were resistant to streptomycin (250 mu g/ml), fou r isolates were resistant to kanamycin (10 mu g/ml), and one isolate w as resistant to fusicic acid (10 mu g/ml). In mating experiments with Enterococcus faecalis JH2-2 as recipient, tetracycline, erythromycin, and kanamycin genes were transferred separately to the recipient strai n at a rate of 10(-7) transconjugants/recipient cell.