Four isolates with this genotype were found in the present work, but we can not confirm whether they belong to the above clone. Conclusion In summary, the resistance against erythromycin, single or together to tetracycline, is due to a wide combination of resistance genes in Spanish GAS. Erythromycin resistance is mainly consequence LCZ696 of clonal spread of emm4T4, emm75T25, both associated with M phenotype and SmaI non-restricted, and emm28T28. Whereas tetracycline resistance and coresistance is due to clonal spread of emm77T28 and emm11T11,
respectively, all SmaI restricted. Methods Bacterial isolates Between 1994 and 2006, 898 GAS isolates were submitted for their characterisation to the Streptococcal
Reference Laboratory from 75 Hospitals and Public Health Laboratories in 32 Spanish provinces. GAS identification was confirmed by colony morphology, β-haemolysis on blood agar, a latex agglutination assay (Slidex, Streptokit, BioMerieux, Marcy-LÂ´Etoile, France), and by using the rapid ID 32 STREP kit (BioMerieux, Marcy-LÂ´Etoile, France). The erythromycin- and tetracycline-resistant isolates were selected as the study population (see section antimicrobial susceptibility tests). This population (337 isolates) was collected from a wide spectrum of clinical backgrounds, including necrotising fasciitis (3), cellulitis and other skin infections (67), streptococcal toxic shock syndrome (13), sepsis and meningitis (17), respiratory infection (5), bone MK5108 infection and rheumatic fever (4), genital infection (20), otitis (12),conjunctivitis (1), scarlet fever (70) and pharyngotonsillitis (80), as well as from asymptomatic carriers (45). For the latter status, the GAS isolates were recovered from oropharyngeal swabs. A limitation of the study was due to the voluntary nature of the submission of these strains, producing a bias in the annual number. Antimicrobial susceptibility tests The minimum inhibitory concentrations (MICs) of penicillin, vancomycin, erythromycin, clindamycin, tetracycline and
rifampin were determined using the E-test (AB Biodisk, Solna, Sweden) following the standard method . Susceptibility Dynein results were categorized according to the criteria of the Clinical and Laboratory Standards Institute . The erythromycin- (MIC ≥ 1 mg/L) and tetracycline-resistant (MIC ≥ 8 mg/L) isolates were then selected as the study population. Streptococcus pneumoniae ATCC 49619 was used as control. Detection of the macrolide resistance phenotype Erythromycin-resistant isolates were classified on the basis of their susceptibility patterns as shown by double-disk tests involving erythromycin (15 μg) and clindamycin (2 μg ) disks (Becton Dickinson Microbiology Systems, Cockeysville, MD, USA) .