RESUMO
OBJECTIVES: To determine the prevalence of macrolide and streptogramin resistance in Streptococcus mitis isolates from neutropenic patients and to identify mechanisms of macrolide and streptogramin resistance in resistant isolates. METHODS: MICs of erythromycin, spiramycin, lincomycin and pristinamycin were determined for S. mitis isolates. Macrolide-resistance genes were characterized by PCR and ribosomal mutations by sequencing. RESULTS: A total of 169 S. mitis isolates were recovered from 66 patients at the Tunisian Bone Marrow Transplant Centre. Of these, 120 (70%) were non-susceptible to erythromycin and one was resistant to pristinamycin; 48.5% of isolates had an MLSB phenotype with cross-resistance between erythromycin, spiramycin and lincomycin, 4% had a dissociated MLSB phenotype with resistance to erythromycin and spiramycin but apparent susceptibility to lincomycin and 47.5% displayed the M phenotype. Resistance determinants were characterized in 33 isolates. Ten of 14 isolates with the cross MLSB resistance contained an ermB-like gene and four a combination of ermB- and mefA-like genes. Four of the five isolates with a dissociated MLSB phenotype contained ermB-like and one a combination of ermB- and mefA-like genes. All the 14 isolates with an M phenotype contained mefA-like genes. The pristinamycin-resistant strain had G105 and A108 substitutions in the conserved C terminus of the L22 ribosomal protein. CONCLUSIONS: The prevalence of macrolide resistance is high in S. mitis from neutropenic patients and is due to the spread of ermB- or mefA-like genes alone or combined. Resistance to streptogramins is rare and in this case associated with ribosomal mutation.
Assuntos
Antibacterianos/farmacologia , Macrolídeos/farmacologia , Neutropenia/microbiologia , Infecções Estreptocócicas/microbiologia , Streptococcus mitis/efeitos dos fármacos , Streptococcus mitis/genética , Estreptograminas/farmacologia , Sequência de Aminoácidos , Transplante de Medula Óssea , Primers do DNA , Farmacorresistência Bacteriana , Eritromicina/farmacologia , Genótipo , Humanos , Hospedeiro Imunocomprometido , Testes de Sensibilidade Microbiana , Dados de Sequência Molecular , Fenótipo , Pristinamicina/farmacologia , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
Activity of rifampin against 129 Streptococcus mitis isolates obtained from patients with hematologic cancer was investigated. One hundred twenty-five strains were susceptible to rifampin, and 4 were resistant (MIC = 32 to 64 microg/ml). Resistance to rifampin was related to mutations in the rpoB gene: His(526)Asn in three strains and His(526)Asp in one strain.
