Rapid variations in the macrolide resistance frequency, phenotypes and clones of group A streptococci from pharyngeal colonisation and infections, 2000 to 2006

Abstract number: 1733_253

Rolo D., Custódio S., Nunes A., Cabral R., Rato M., Oliveira V., Tavares D.A., Pires R., Morais A., Faria M.C., Barros R.M., Peres I., Trigueiro G., Cardoso C., Marques J.G., Santos-Sanches I.

Objectives: To compare the macrolide resistance frequencies, phenotypes, clones and population structure among isolates of Group A streptococci (GAS) from pharyngeal colonisation and infections over time.

Methods: A total of 1,425 GAS collected during 2000–2006 in Portugal from asymptomatic pharyngeal carriage (CA, n = 938) and tonsillitis/pharyngitis (TS, n = 487) of children and adults were tested for macrolide resistance frequency and phenotypes (M or MLSB) by disk diffusion. The macrolide-resistant (MR) isolates from CA (n = 153) and TS (n = 101) were characterised for serologic T-types and for SmaI or SfiI DNA-band Pulsed-Field Gel Electrophoresis (PFGE) patterns. Isolates of major PFGE patterns were tested by PCR and sequencing for emm-types and for sequence types (ST) by Multi Locus Sequence Typing (MLST).

Results: Resistance to macrolides gradually increased since 2000 (12%) to 2003 (43%) and decreased since 2004 (21%) to 2006 (13%) in TS isolates and the same trend was observed in CA isolates: an increase since 2000 (9%) to 2003 (28%) and a decrease until 2006 (14%). The M phenotype among CA isolates increased rapidly from 40% in 2000 to 88% in 2001, became stable (>80%) during 2000/04 and was undetected in 2005/06, while among TS isolates was almost constant from 2000/05 (>50%) and decreased to 17% in 2006. In parallel, the MLSB phenotype became dominant in 2005/06. Most (76%) of the MR isolates were of three M phenotype international lineages that emerged among isolates of both origins in different years: ST39 (PFGE AA-emm4,emm75-T8.25Imp19,T4,others), ST36 (PFGE R-emm12-T12,others) and ST28 (PFGE Z-emm1-T1). ST28 emerged in 2000/01, was dominant in 2001 (71%) and disappeared in 2003. ST39 and ST36 emerged in 2001/02, were dominant in 2003 (c.a.40%) and disappeared in 2005/06. One MLSB phenotype lineage, ST52 (PFGE F or PFGE AK-emm28-T28), resistant to bacitracin and also seen as epidemic worldwide emerged in 2000/02 and in 2006 included all the MLSB isolates from CA and TS.

Conclusions: The epidemiology of GAS from throat colonisation and infection underwent major shifts during 2000–2006, which included: (i) decrease in macrolide resistance since 2003 to 2006; (ii) inversions of macrolide resistance phenotypes in 2000 and 2005; (iii) fluctuation and replacement of major macrolide-resistant clones. In this study, lineage ST52 of MLSB phenotype recognized as capable of causing a broad range of streptococcal infections was first detected in carriers.

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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