Characterization of ermB Gene Transposition by Tn 1545 and Tn 917 in Macrolide-Resistant Streptococcus pneumoniae Isolates

Abstract

ABSTRACT In Streptococcus pneumoniae , the ermB gene is carried by transposons, such as Tn 917 and Tn 1545 . This study investigated the relationship between macrolide resistance and the presence of the ermB gene on Tn 917 or Tn 1545 in 84 Japanese pneumococcal isolates. Macrolide-resistant strains were classified into two groups as follows. Group 1 (19 strains) showed a tendency to high resistance to erythromycin (MIC at which 50% of isolates are inhibited, 4 mg/liter; MIC at which 90% of isolates are inhibited [MIC 90 ], 128 mg/liter) but susceptibility to rokitamycin (MIC 90 , 1 mg/liter), with the ermB gene located on Tn 1545 . Group 2 (65 strains) showed a tendency to high resistance to both antibiotics (MIC 90 s for both erythromycin and rokitamycin, >128 mg/liter), with the ermB gene located on Tn 917 . There were no strains with constitutive macrolide resistance in either group. All of the strains in group 2 had a deletion in the promoter region of ermB and an insertion of the TAAA motif in the leader peptide. The results of pulsed-field gel electrophoresis and serogrouping showed that Tn 1545 spread clonally while Tn 917 spread both horizontally and clonally. In conclusion, in Japanese macrolide-resistant S. pneumoniae isolates, the ermB gene is carried and spread primarily by Tn 917 .