Prevalence and mechanism of resistance against macrolides and lincosamidesin Streptococcus suis isolates

Eighty-seven Streptococcus suis isolates recovered in 1999-2000 from diseas ed pigs, all from different farms, were screened for resistance against mac rolide and lincosamide antibiotics by the disk diffusion and agar dilution test and a PCR assay, amplifying the ermB gene and the mefA/E gene. Seventy -one percent of the isolates showed constitutive resistance to macrolide an d lincosamide antibiotics (MLSB-phenotype). All these isolates were positiv e for the ermB gene in the PCR, but negative for the mefA/E gene. For all s trains minimum inhibitory concentrations (MIC) against five other antimicro bial agents were determined. All strains were susceptible to penicillin. Ni nety-nine percent of the isolates were susceptible to enrofloxacin and tiam ulin. Eighty-five percent of the strains were resistant to doxycycline. A 5 40 bp fragment of the ermB genes of eight S. suis strains was sequenced and compared with ermB genes of five S. pneumoniae and five S. pyogenes strain s of human origin. A 100% homology was found between these fragments in sev en S. suis, one S. pneumoniae and three of the S. pyogenes isolates. This study demonstrates that resistance against macrolides, lincosamides an d streptogramin B is widespread in S. suis and mediated by ribosome methyla tion, encoded by the el-MB gene. (C) 2001 Elsevier Science B.V. All rights reserved.