engleski

Characterisation of macrolide-resistant pneumococcal strains in Zagreb region.

Objectives: Increase in pneumococcal resistance to macrolides is particularly high in Croatia in the last years. Macrolide resistance in Zagreb region raised significantly from 25% in 2005 to 40% in 2008, and the same increase was detected two years later in other parts of country as well. The aim of this study was to characterize macrolide-resistant strains from Zagreb region in dependence of their phenotypic traits. Methods: A total of 93 macrolide-resistant Streptococcus pneumoniae strains were obtained in two-month period from nasopharyngeal swabs collected from 634 children aged 1-15 with a mean age of three years. Minimal inhibitory concentrations was determined for penicillin G, amoxicillin, ceftriaxone, cefuroxime, meropenem, erythromycin, azithromycin and clarithromycin, and serotyping of the strains was carried out by latex agglutination and Neufeld quellung test. Double-disk test (erythromycin + clindamycin) was used for characterization of resistant phenotype of macrolide-resistant strains. Results: The co-resistance to penicillin was determined in 31 (33.3%) strains with a 12.9% of highly resistant S. pneumoniae isolates (MIC range 2-4 mcg/ml). The resistance to other beta-lactams was lower with less than 10% of non-susceptibility to ceftriaxone and only 6.4% isolates intermediately resistant to amoxicillin. Macrolides showed decreased activity against tested strains, with resistance being 38.7%, 36.6% and 33.3% for erythromycin, azithromycin and clarithromycin, respectively. MIC90 of azithromycin and clarithromycin was 512 mcg/ml, while MIC90 for erythromycin was 1024 mcg/ml. The most common serotypes were 19F, and other serotypes (1, 2, 3, 4, 5, 8, 6A, 6B, 6C, 7, 8, 9, 10, 11, 14, 15, 17, 18C, 19A, 19C and 23F) were detected with a low frequency. Constitutive MLSB phenotype was predominant and Mphenotype was detected in 17.1% of the resistant strains. Conclusion: In contrast to other parts of country where prevalence of serotype 19A is the most higher, the macrolide-resistance in S. pneumoniae nasopharyngeal isolates collected in Zagreb region was associated with serotype 19F. Continued surveillance is necessary, and further studies are needed in order to detect emerging serotypes and multidrug resistant clones. The results of present study suggest the possibility of clonal dissemination of macrolide-resistant pneumococcal strains harbouring both erm (B) and mef (E) genes in Zagreb region.

Streptococcus pneumoniae; antibiotics; macrolide resistance

nije evidentirano