Trends in Macrolide Resistance for Streptococcus pyogenes, Streptococcus agalactiae and Streptococcus pneumoniae and its Association with Social Clustering in Argentina

The aim of this work was to study and compare macrolide resistance patterns among Streptococcus pneumoniae, Streptococcus agalactiae and Streptococcus pyogenes, to describe the phenotypes of macrolide-lincosamide resistance and to further investigate associations between macrolide resistance and social clustering. Susceptibility data were obtained from 4 clinical microbiology laboratories in Bariloche, Argentina for the period 2002- 2008. Patients were differentiated in two population clusters according to the institution they attended (public or private). A total of 4310 strains were studied: 2615 S. pyogenes, 995 S. agalactiae and 700 isolates of S.pneumoniae. Erythromycin resistance rates over the study period were 1.5% for S. pyogenes, 7.8% for S. agalactiae and 11.3% for S. pneumoniae. For the complete study group, these values differed significantly among species (contingency table  2 = 164.52, p<0.0001). Resistance in S.pyogenes and S. pneumoniae showed irregular trends whilst S. agalactiae showed an increasing tendency during the whole period appearing to be a better indicator of the trends in macrolide resistance. A dual character MLSB phenotype of both inducible and constitutive resistance was observed in S. agalactiae only. Resistance in isolates from the population attending private institutions was significantly higher than those attending the public hospital (S. pyogenes, (1.9 vs. 0.6,  2 = 5.851, p<0.025); S. pneumoniae, 19.1 vs. 7.0 ( 2 = 21.98, p<0.001), and. S. agalactiae, 12.4 vs. 3.8 ( 2 = 24.5, p<0.001)). In conclusion, macrolides resistance rates during 2002-2008 were significantly different for S. pyogenes, S. agalactiae and S.pneumoniae. We also found significant variations in macrolide resistance levels in different population groups.