Phenotypes and genotypes of erythromycin-resistant groupA streptococci in Barcelona

Abstract number: P1728

Domenech A., Rolo D., Calatayud L., Tubau F., Ayats J., Martín R., Liñares J., Ardanuy C.

Objective: The aim of this study was to analyze the evolution of phenotypes, genotypes and macrolide resistance genes of Streptococcus pyogenes (GAS) isolated from invasive and non-invasive disease among adults patients from 1998 to 2007.

Methods: A total of 445 GAS strains were isolated in our hospital during the study period. Antibiotic susceptibility was studied by microdilution and macrolide resistance phenotypes by disk diffusion. Molecular typing was performed by PFGE (SmaI) and emm-typing, and selected strains were studied by MLST. Macrolide resistant genes and those of Tn916-family of transposons were detected by PCR.

Results: During the study period 95 (21%) erythromycin resistant isolates were detected. Of them, 50 occurred in men (53%). The medium age was 49 (SD19, range 18–90). The 59% of them were isolated from soft-tissue infections, 15% from respiratory tract specimens and 6% from pharyngitis. By two year period the rates of erythromycin-resistant (EryR) were: 18.42% (1998–1999), 15.58% (2000–2001), 45.6% (2002–2003), 25.49% (2004–2005) and 9.84% (2006–2007). Thirty-six (37.9%) strains had M phenotype and 59 (62.1%) had MLSB phenotype (39 cMLSB and 20 iMLSB). The proportion of M decreased throughout the study period (from 10/14 in 1998–99 to 4/12 in 2006–2007, p = 0.05). All 26 M phenotype GAS studied had mefA gene. Of 21cMLSB studied 20 had ermB and 1 had ermTR genes. Five iMLSB GAS had ermTR and 8 had ermB. No tetracycline resistance nor tetM gene was detected among M phenotype GAS. All GAS harbouring ermB gene had tetM gene and the majority of them (75%8) were related to Tn916-family of transposons (Tn6002 and Tn1545). Three GAS with ermTR gene were resistant to tetracycline related to tetM gene probably harboured by Tn916 transposon. The predominant genotypes were emm11-ST403 (12%), emm4-ST39 (7%) and emm25-ST350 (n = 6%).

Conclusion: Macrolide resistance rates among GAS isolated from adults fluctuates throughout the study period. The peak observed in 2002–2003 period was associated with an outbreak due to emm25-ST350 among injection drug users. The increased rates of MLSB phenotype were associated with the spread of Tn916-family of transposons harbouring ermB and tetM genes.

Session Details

Date: 16/05/2009
Time: 00:00-00:00
Session name: 19th European Congress of Clinical Microbiology and Infectious Diseases
Location: Helsinki, Finland, 16 - 19 May 2009
Presentation type:
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