Detection of the aminoglycosidestreptothricin resistance gene cluster ant(6)-sat4-aph(3´)-III in commensal viridans group streptococci

High-level aminoglycoside resistance was assessed in 190 commensal erythromycin-resistant α-hemolytic streptococcal strains. Of these, seven were als aminoglycoside-resistant: one Streptococcus mitis strain was resistant to high levels of kanamycin and carried the aph(3´)-III gene, four S. mitis strains were resistant to high levels of streptomycin and lacked aminoglycoside-modifying enzymes, and two S. oralis strains that were resistant to high levels of kanamycin and streptomycin harbored both the aph(3´)-III and the ant(6) genes. The two S. oralis strains also carried the ant(6)-sat4-aph(3´´)-III aminoglycoside-streptothricin resistance gene cluster, but it was not contained in a Tn5405-like structure. The presence of this resistance gene cluster in commensal streptococci suggests an exchange of resistance genes between these bacteria and enterococci or staphylococci. [Int Microbiol 2007; 10(1):57-60]