Population structure of Spanish mef-PCR positive Streptococcus pneumoniae clinical isolates

Abstract number: 1733_495

Gómez G-de la Pedrosa E., van der Linden M., Morosini M.I., Galán J.C., Baquero F., Reinert R.R., Cantón R.

Objectives: To determine the population structure of a collection of mef-PCR positive Streptococcus pneumoniae clinical isolates recovered in different Spanish hospitals. Prevalence of associated erythromycin resistance determinants and phenotypes were also screened.

Methods: A PCR assay was performed to identify erythromycin resistance genes (ermB or mef) in a collection of 712 clinical isolates recovered in Spain from 1999 through 2003. All mef-PCR positive S. pneumoniae strains (n = 46) were selected for further population structure analysis (serotyping with Neufeld's Quellung method, PFGE with SmaI digestion, and MLST with the standard 7 housekeeping loci scheme). Susceptibility testing was performed by the standard microdilution technique (CLSI) and resistance phenotypes by diffusion assay using commercial erythromycin, clindamycin, and rokitamycin disks. A multiplex-PCR was designed to distinguish between mef(A) and mef(E). msr(D) determinant (mel gene) was also detected by PCR.

Results: Resistance values among 46 selected mef positive isolates were: penicillin, 67.3% (intermediate + resistant), clindamycin, 52.2%, and tetracycline 56.5%. No telithromycin resistance was found (MIC range, 0.03–1 mg/L) but one isolate was resistant to levofloxacin (MIC, 8 mg/L). Interestingly, 4 mef positive isolates (8.7%) showed erythromycin MICs in the susceptible range (0.12 mg/L), but increased ≥32 mg/L endowing the M phenotype when plated on increased concentrations of erythromycin. The M and MLSB phenotypes in erythromycin resistant isolates were observed in 45.2% and 54.72% of isolates, respectively. The presence of both erm and mef determinants was found in 50% of isolates. All mef determinants belonged to mef(E) subclass and all isolates presented the msr(D) gene. Serotype distribution was as follows: 14, 21.7%; 19F, 19.5%; 19A, 15.2%; 6B, 6.5%; 9V 6.5%; and others, 30.6%. Most isolates belonging to the same serotype showed similar PFGE patterns. England^14–9 and Taiwan^19F-14 multiresistant clonal complexes were represented within mef positive isolates and Spain^23F-1, Poland^6B-20, Sweden^15A-25 and Spain 6B among erm and mef positive isolates.

Conclusions: A high proportion of S. pneumoniae isolates harbouring the mef gene in our collection also presents the ermB determinant. Nearly all of them displayed the MLSB phenotype. A complex population structure was found in our mef positive S. pneumoniae collection.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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