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.