| Streptococcus suis is a Gram-positive bacterium of increasing importance in pig production
throughout the world. Although conjugative transfer of erythromycin, tetracycline,
or kanamycin resistance that is possibly mediated by a conjugative transposon
has been reported in S. suis, genetic organization of antibiotic resistance transposons isolated from
S. suis has not thus far been reported. Here we report a new chloramphenicol resistance
transposon (TnSs1) found in a field isolate of S. suis. The transposon consists of a chloramphenicol acetyltransferase gene sandwiched
between two directly repeated IS6-family elements (IS214L and IS214R). Polymerase chain reaction and Southern hybridization analyses indicated
that another field isolate harbored the same transposon in a different
location on the chromosome. A transposition assay done with a temperature
sensitive suicide vector showed that, among the seven TnSs1 mutants tested in this study, six formed a cointegrate between the S. suis chromosome and the vector, with the generation of a third copy of the
IS214 element, and one carried one copy of TnSs1 on the chromosome as a result of a subsequent resolution step. These results
demonstrate that TnSs1 is an active mobile genetic element. (Molecular Bacteriology Section,
Department of Infectious Diseases TEL +81-29-838-7743) |