Comparison of macrolide-resistant and macrolide-susceptible populations of group A streptococci from asymptomatic oropharyngeal colonisation in Portugal

Abstract number: P1714

Pires R., Rolo D., Almeida J.F., Brito-Avô A., Morais A., Gonçalo-Marques J., Santos-Sanches I.

Objectives: To assess the structure and evolution of macrolide resistant and susceptible populations of group A streptococci (GAS) from asymptomatic oropharyngeal colonisation during 2000 to 2005.

Methods: A total of 850 GAS collected from healthy carriers at day care centres (DCC) were tested for macrolide resistance frequency and phenotypes (M or MLSB) by disk diffusion. Out of these, all (n = 141) macrolide resistant (MR) isolates and part of the macrolide susceptible (MS) isolates [368 isolates collected at DCC where high (geqslant R: gt-or-equal, slanted15%) colonisation rates were observed] were characterised by SmaI or Cfr9I DNA-band pulsed-field gel electrophoresis (PFGE) profiling. Representatives of different PFGE patterns were characterised by T-typing, emm-typing and multilocus sequence typing (MLST).

Results: Resistance to macrolides was approximately 10% in 2000–02, 28% in 2003, 20% in 2004 and 3% in 2005. M phenotype isolates increased from 40% in 2000 to >80% during 2001–04 and were not detected in 2005. In parallel the MLSB phenotype isolates were prevalent in 2000 (60%) and in 2005 (100%).

Three major clonal lineages accounted for the majority of the M phenotype isolates (70% of 117 isolates) and were prevalent in different years: ST28 (emm1;emm107/T1/PFGE.CX) in 2001, ST36 (emm12/T12;others/PFGE.AP) in 2002/03 and ST39 (emm4;emmstMrp6/T4;others/PFGE.CZ) in 2004.

Also three major clonal lineages accounted for the majority of the MLSB phenotype isolates (63% of 24 isolates) and were as well detected in different years: ST46 (emm22;emm73/T13/PFGE.A) in 2000/01 and 2003, ST52/bacitracin-resistant (emm28/T28/PFGE.F) in 2003/04, and ST403 (emm11/T11;NT/PFGE.BO) in 2004/05.

Most of the MS isolates (69%) were included in six clones also variable in frequency and year of detection: ST55 (emm79/T2.12/PFGE.BH), ST382 (emm1;emm6/T6/PFGE.AD), ST36 (emm12/T3;other/PFGE.AP), ST403 (emm1/T1/PFGE.BG), ST28 (emm1/T1/PFGE.X), and ST-not assigned (emm12/T12/PFGE.AB).

Conclusions: The epidemiology of MR and MS GAS from asymptomatic colonisation changed rapidly during 2000–05. However, several lineages of MR and MS were identified which were described as prevalent and capable of causing a broad range of streptococcal infections in Europe. Two lineages (ST36 and ST403) were found to comprise MR and MS isolates of different T, emm and PFGE types. This study stresses the role of carriers as reservoirs of particular strains either resistant or susceptible to antimicrobials with high ability to colonize and disseminate.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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