(T)-Mediated Macrolide-Lincosamide Resistance in Streptococcus suis.

To investigate the presence and location of (T) in clinical Streptococcus suis isolates and explore the transmission ability and fitness cost of (T)-carrying mobile genetic elements among S. suis isolates, MICs were determined by broth microdilution. The presence of (T) in S. suis was detected by PCR. The genetic environment of (T) in S. suis was explored by whole-genome sequencing (WGS) analysis. Intraspecies and interspecies transmission were examined by electrotransformation. The fitness cost associated with the carriage of an (T)-harboring plasmid or an integrative and conjugative element (ICE) was examined by competition experiments. Of 237 nonduplicate strains, (T) was detected in 2 S. suis strains (SC262-ST954 and SC117-ST1314), with its location on a 5,125-bp plasmid in S. suis SC262 and on a 64,013-bp ICESC117 in S. suis SC117, respectively. Both the (T)-carrying plasmid pSC262 and the ICESC117 were transmissible by transformation. Plasmid pSC262 can replicate and express macrolide-lincosamide resistance in heterologous hosts, including S. aureus and S. pneumoniae. Both the (T)-carrying plasmid and the ICE posed a fitness cost to the host S. suis isolate. To the best of our knowledge, this is the first report of the macrolide-lincosamide-streptogramin B resistance gene (T) in S. suis. Its location on a plasmid or an ICE will aid in its transmission. The low detection rate of (T) gene among the S. suis population might be due to the fitness cost of the (T)-carrying plasmid and ICE. Macrolide and lincosamide resistance due to the presence of (T) have posed a challenge for the treatment of Gram-positive pathogens. Although the low detection rate of (T) gene among the S. suis population due to the fitness cost of the (T)-carrying plasmid and ICE, the presence of (T) in S. suis and its potential transmission to other Gram-positive pathogens will be of important significance.