Mecanismos de resistencia a antibióticos macrólidos, lincosamidas y estreptograminas en streptococcus y enterococcus

Résumé

Objetive: Characterization of macrolide, lincosamide and streptogramin (MLS) resistance mechanisms in Streptococcus and Enterococcus in La Rioja, from 1996 to 2001. Distribution of erythromcyin resistance phenotypes and involved mechanisms were studied for both genera, as well as temporary evolution and clonal diversity for erythromycin-resistant Streptococcus isolates. A new gene that we called msrC was described for an enterococcal species. Conclusions: High erythromycin resistance rates were detected for beta-haemolytic group A, B, C and G Streptococcus isolates in La Rioja (13-25%) and it was even higher for S. pneumoniae isolates (54%). Percentages of erythromycin-resistant isolates decreased, from 35 to 20% and from 64 to 47%, for S. pyogenes and S. pneumoniae, respectively. M resistance phenotype was the most frequently found among erythromycin-resistant S. pyogenes isolates (80%). MLSB resistance phenotype was exclusive for beta-haemolytic Streptococcus group C and G, and it was >97% for S. agalactiae and S. pneumoniae. mef(A) or mef(E) genes, associated with M resistance phenotype, and erm(B) or erm(TR) genes, associated with MLSB resistance phenotype, were predominant in Streptococcus, depending on the species. Beta-haemolytic erythromycin-resistant Streptococcus isolates with the same clonal origin were detected in different years of the study. The erm(B) gene was detected in all erythromycin highly-resistant Enterococcus isolates, with the exception of one isolate of E. faecium which presented the erm(A) gene. A new gene that we called msrC was detected in all E. faecium isolates, independently of their erythromycin resistance pattern. The remaining species of Enterococcus analyzed did not present msrC. The msrC gene, described in E. faecium, contains 1479 bp and it has 53% identity with msr(A) gene, described in Staphylococcus and related to macrolide and streptogramin B resistance in this bacteria. The msrC gene codifies a protein of 492 amino acids and it belongs to a family of efflux pumps genes. An erythromycin efflux system, dependent on energy, was seen in E. faecium isolates with different levels of resistance to this macrolide. The efflux pump MsrC could be related to this erythromycin efflux.