The aim of this study was to describe the genetic characteristics of Streptococcus pyogenes showing the MLS B phenotype of macrolide resistance from 1999 to 2005 in Spain and to highlight the substantial increase in these isolates in the last few years. The antimicrobial susceptibilities of 17,232 group A streptococci isolated from Madrid and Gipuzkoa from 1999 to 2005 were studied. The presence of the resistance genes ermA, ermB, mef, tetM, and tetO and the presence of the intTn and xis genes of the Tn916-Tn1545 transposon family were studied in a sample of 739 MLS B -resistant isolates. The epidemiological relationships among these isolates were analyzed by emm typing, T typing, and multilocus sequence typing. Erythromycin resistance was found in 21.3% of the isolates analyzed (annual variation of 14.3% to 28.9%). Until 2003, most erythromycin-resistant isolates showed the M phenotype, but in 2004 and 2005, about 50% of isolates showed the MLS B phenotype. Among the MLS B -resistant isolates studied, 16 clones were identified. The most prevalent clone was a strange emm11/ T11/ST403 clone with a null yqiL allele. All but one of the 463 emm11/T11/ST403 isolates carried the ermB, tetM, intTn, and xis genes. The second most prevalent MLS B -resistant clone was emm28/T28/ST52, which comprised two subclones: one bacitracin-resistant, tetracycline-susceptible subclone carrying the ermB gene (n ‫؍‬ 115) and another bacitracin-susceptible, tetracycline-resistant subclone carrying the ermB and tetM genes (n ‫؍‬ 33). The rapid diffusion of these two clones, and especially of emm11/T11/ST403, caused the large increase in MLS Bresistant S. pyogenes isolates in Spain, suggesting a potential ability for international dissemination.Streptococcus pyogenes is a pathogen with worldwide distribution that causes a broad spectrum of infections, from uncomplicated pharyngitis to severe life-threatening infections (6). In the absence of a ␤-lactam allergy, the treatment of choice is penicillin, while the first-line alternative treatments are macrolides or lincosamides. There are two main phenotypes of macrolide resistance: the M phenotype, mediated by the mef genes (8), which confer low-level resistance to 14-and 15-membered macrolides but not to 16-membered macrolides, lincosamides, or streptogramin B, and the MLS B phenotype, mediated by the erm genes (20, 34), which confer resistance to macrolides, lincosamides, and streptogramin B antimicrobial agents. This latter phenotype can be constitutive, generally mediated by the ermB gene, or inducible, generally mediated by the ermA subclass TR (ermA) gene (31). Other mechanisms of resistance to macrolides or lincosamides in S. pyogenes (e.g., mutations in ribosomal proteins) are infrequently involved and currently have little clinical impact (4, 17).The factor most directly associated with the increase in antimicrobial resistance is the high level of antibiotic consumption among the population (2, 15). Nonetheless, the final cause of a higher or lower prevalence of antimicrobial resista...

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Petters MF, Zanen HC, Brenner D J: Phenotypic characterization and DNA relatedness in human fecal isolates ofAeromonas spp. J ournal of Clinical Microbiology 1989, 27: 132-138. 5. Janda JM, Duffey PS: Mesophilic aeromonadsin human disease: current taxonomy, laboratory identification, and infectious disease spectrum. Reviews of Infectious Diseases 1988,10: 980-997. 6. Washington JA: Aeromonas hydrophila in clinical bacteriologic specimens. Annals of Internal Medicine 1972, 76: 611--614. 7. Ramsay AM, Rosenbaum B J, Yarbrough CL, Holz JA:Aeromonas hydrophila sepsis in a patient undergoing hemodialysis therapy.

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A total of 103 (0.7%) of 14,236 Streptococcus pneumoniae isolates collected in four Spanish hospitals from 1989 to 2003 were resistant to rifampin (MICs, 4 to 512 g/ml). Only sixty-one (59.2%) of these isolates were available for molecular characterization. Resistance was mostly related to human immunodeficiency virus (HIV) infection in adult patients and to conjunctivitis in children. Thirty-six different pulsed-field gel electrophoresis patterns were identified among resistant isolates, five of which were related to international clones (Spain 23F -1, Spain 6B -2, Spain 9V -3, Spain 14 -5, and clone C of serotype 19F), and accounted for 49.2% of resistant isolates. Single sense mutations at cluster N or I of the rpoB gene were found in 39 isolates, while double mutations, either at cluster I, at clusters I and II, or at clusters N and III, were found in 14 isolates. The involvement of the mutations in rifampin resistance was confirmed by genetic transformation. Single mutations at clusters N and I conferred MICs of 2 g/ml and 4 to 32 g/ml, respectively. Eight isolates showed high degrees of nucleotide sequence variations (2.3 to 10.8%) in rpoB, suggesting a recombinational origin for these isolates, for which viridans group streptococci are their potential gene donors. Although the majority of rifampin-resistant isolates were isolated from individual patients without temporal or geographical relationships, the clonal dissemination of rifampin-resistant isolates was observed among 12 HIV-infected patients in the two hospitals with higher rates of resistance.