[Phenotypes and genetic mechanisms of resistance to macrolides and lincosamides in viridans group streptococci]. / Fenotipos y mecanismos genéticos de resistencia a macrólidos y lincosamidas en estreptococos del grupo viridans.

Viridans group streptococci (VGS) are part of the oropharyngeal, intestinal and genital flora, but they may cause endocarditis and bacteremia in susceptible patients. Penicillin- and macrolide-resistant strains are increasing every year. The aim of this study was to investigate genetic mechanisms of resistance to macrolides in clinically relevant isolates. We identified 85 isolates from January 2004 to June 2006. Susceptibility to penicillin, cefotaxime, erythromycin, clindamycin and gentamycin was determined. A resistance phenotype was assigned according to the disk approximation test (erythromycin-clindamycin). The mechanism of resistance was determined by PCR for the following genes: ermB, ermA, ermC, ermA (TR) and mefA/E. We identified 51 isolates belonging to Streptococcus anginosus species, most of which were obtained from abdominal abscesses, and 34 isolates belonging to other species, most of which were obtained from blood cultures. The macrolide resistance rate was 28.2% (24/85). The MLS(B) phenotype was observed in 66.7% of the isolates, primarily in the S. anginosus group. The M phenotype was predominant in S. mitis and S. oralis. Isolates that expressed the constitutive MLS(B) phenotype carried the ermB gene, and those that expressed the inducible MLSB phenotype carried the ermA gene. Isolates that expressed the M phenotype carried the mefA/E gene. There was coresistance with penicillin in 20.8% (5/24) of the isolates. Coresistance with penicillin was low. These results suggest that screening for macrolide resistance in VGS would be desirable because of the potential transmission of resistance genes to other pathogenic streptococci.

Fenotipos y mecanismos genéticos de resistencia a macrólidos y lincosamidas en estreptococos del grupo viridans / Phenotypes and genetic mechanisms of resistance to macrolides and lincosamides in viridans group streptococci

Los estreptococos del grupo viridans forman parte de la flora orofaríngea, intestinal y genital, pero pueden causar endocarditis y bacteriemia en pacientes susceptibles. Cada vez se describen más cepas resistentes a las penicilinas y a los macrólidos. El objetivo de nuestro estudio fue conocer los mecanismos de resistencia a los macrólidos en aislamientos con significación clínica. De enero de 2004 a junio de 2006 se identificaron 85 cepas de estreptococos del grupo viridans. Se determinó la sensibilidad a penicilina, cefotaxima, eritromicina, clindamicina y gentamicina. Se estableció el fenotipo de resistencia a los macrólidos mediante aproximación de discos (eritromicina-clindamicina). Se detectó el mecanismo genético de resistencia mediante PCR para los genes ermB, ermA, ermC, ermA (TR) y mefA/E. Se identificaron 51 cepas pertenecientes a especies del grupo anginosus, obtenidas mayoritariamente de abscesos abdominales, y 34 cepas de otras especies, obtenidas mayoritariamente de hemocultivos. La tasa de resistencia a los macrólidos fue del 28,2% (24/85). El fenotipo MLSB se observó en el 66,7% de las cepas, principalmente del grupo anginosus. El fenotipo M predominó en S. mitis y S. oralis. En las cepas con fenotipo MLSB constitutivo se detectó el gen ermB, mientras que en las cepas con expresión inducible se detectó el gen ermA. En las cepas con fenotipo M se detectó el gen mefA/E. Se observó corresistencia con penicilina en el 20,8% (5/24) de las cepas. La resistencia a los macrólidos en los estreptococos del grupo viridans es ligeramente menor que la observada en otros estudios. Destacamos mayor resistencia y presencia del fenotipo MLSB en cepas del grupo anginosus, y del fenotipo M en las restantes especies, lo cual podría estar relacionado con el origen anatómico de las cepas. La corresistencia a la penicilina fue baja. Sería recomendable vigilar periódicamente la resistencia a los macrólidos en los estreptococos del grupo viridans, posibles transmisores de resistencia a otras especies de estreptococos patógenos

Viridans group streptococci (VGS) are part of the oropharyngeal, intestinal and genital flora, but they may cause endocarditis and bacteremia in susceptible patients. Penicillin- and macrolide-resistant strains are increasing every year. The aim of this study was to investigate genetic mechanisms of resistance to macrolides in clinically relevant isolates. We identified 85 isolates from January 2004 to June 2006. Susceptibility to penicillin, cefotaxime, erythromycin, clindamycin and gentamycin was determined. A resistance phenotype was assigned according to the disk approximation test (erythromycin-clindamycin). The mechanism of resistance was determined by PCR for the following genes: ermB, ermA, ermC, ermA (TR) and mefA/E. We identified 51 isolates belonging to Streptococcus anginosus species, most of which were obtained from abdominal abscesses, and 34 isolates belonging to other species, most of which were obtained from blood cultures. The macrolide resistance rate was 28.2% (24/85). The MLSB phenotype was observed in 66.7% of the isolates, primarily in the S. anginosus group. The M phenotype was predominant in S. mitis and S. oralis. Isolates that expressed the constitutive MLSB phenotype carried the ermB gene, and those that expressed the inducible MLSB phenotype carried the ermA gene. Isolates that expressed the M phenotype carried the mefA/E gene. There was coresistance with penicillin in 20.8% (5/24) of the isolates. Coresistance with penicillin was low. These results suggest that screening for macrolide resistance in VGS would be desirable because of the potential transmission of resistance genes to other pathogenic streptococci