Molecular epidemiology of macrolide and tetracycline resistances in commensal Gemella sp. isolates

Abstract

The epidemiologic relatedness of 29 erythromycin-resistant Gemella sp. strains from normal flora, characterized previously, were evaluated by pulsed-field gel electrophoresis (PFGE). Three isolates carried the tet(O) gene and the tet(M) gene. The msr(A) gene was found in two Gemella morbillorum strains in combination with the erm(B) or mef(E) gene. The sequences of the mef(A/E), erm(B), and msr(A) genes showed a high similarity to the corresponding sequences of other gram-positive cocci. All the strains harboring the mef(A/E) gene and the msr(D) gene possessed open reading frame 3 (ORF3)/ORF6. The 16 G. morbillorum isolates represented 15 distinct DNA profiles. Four clusters were identified (>or=80% genetic relatedness). The 12 Gemella haemolysans strains belonged to different PFGE types. The clonal diversity found suggests that horizontal transfer may be the main route through which erythromycin resistance is acquired.

FIG. 1.

Dendrogram depicting the genetic relatedness of 16 commensal G. morbillorum isolates. Similarities are based on Dice coefficients of SmaI macrorestriction profiles demonstrated by PFGE. The 80% similarity was used as a cutoff criterion for comparison of PFGE patterns. The same antimicrobial phenotype and genotype were observed both in genetically closely and unrelated strains, i.e., strains 23 and 135. Abbreviations: S, sputum; PE, pharyngeal exudate; NS, nasal swab sample; BA, bronchial aspirate; A, adult; Ch, child; ERY, erythromycin; TET, tetracycline; MIN, minocycline; Q-D, quinupristin-dalfopristin; TEL, telithromycin.

FIG. 2.

Dendrogram depicting the genetic relatedness of 12 commensal G. haemolysans isolates. Similarities are based on Dice coefficients of SmaI macrorestriction profiles demonstrated by PFGE. The 80% similarity was used as a cutoff criterion for comparison of PFGE patterns. The same antimicrobial phenotype and genotype were observed in genetically unrelated strains, i.e., strains 68, 280, and 70. Abbreviations: S, sputum; PE, pharyngeal exudate; BA, bronchial aspirate; A, adult; Ch, child; ERY, erythromycin; TET, tetracycline; MIN, minocycline; Q-D, quinupristin-dalfopristin.