ABSTRACT
BACKGROUND: Increased levels of macrolide-resistant Streptococcus pyogenes in focal regions of the United States have been reported. The purpose of this study was to determine the antimicrobial susceptibility of a large collection of S. pyogenes isolates from throughout the United States and to elucidate the mechanisms of resistance and genetic relatedness of macrolide-resistant isolates. METHODS: During 2002-2003, a total of 1885 S. pyogenes clinical isolates were obtained from 45 US medical centers. Susceptibility to penicillin, cefdinir, erythromycin, azithromycin, clarithromycin, clindamycin, telithromycin, and levofloxacin was determined. Macrolide resistance phenotypes were determined by double-disk diffusion, and macrolide resistance genotypes were determined by polymerase chain reaction and sequencing. All macrolide-resistant isolates and all isolates recovered from sterile sites were further characterized by pulsed-field gel electrophoresis (PFGE) and emm typing. RESULTS: The majority (85%) of isolates were pharyngeal. Resistance was detected to erythromycin (6.8% of isolates), azithromycin (6.9%), clarithromycin (6.6%), clindamycin (0.5%), telithromycin (0.2%), and levofloxacin (0.05%). The macrolide-resistance phenotype distribution was as follows: macrolide-lincosamide-streptogramin B (MLSB), 56% of isolates (inducible, 47%; constitutive, 9%); and M, 44%. The genotypes detected were as follows: ermA, 46% of isolates (95% with inducible MLSB phenotype); mefA, 43% (all with M phenotype); and ermB, 8.5% (45% with inducible MLSB and 45% with constitutive MLSB). Three isolates with constitutive MLSB phenotypes had 23S ribosomal RNA mutations. The 129 erythromycin-resistant isolates belonged to 28 emm types and 44 PFGE patterns, with 51% of the isolates in 4 major PFGE clones each associated with a predominant emm type (emm75, emm58, emm12, and emm114) and resistance genotype (mefA or ermA)). CONCLUSIONS: The population of macrolide-resistant S. pyogenes isolates in the United States is small, but it includes several large clones with potential for expansion.
Subject(s)
Drug Resistance, Multiple, Bacterial , Macrolides/pharmacology , Streptococcal Infections/epidemiology , Streptococcal Infections/microbiology , Streptococcus pyogenes/drug effects , Adolescent , Adult , Aged , Anti-Bacterial Agents , Child , Child, Preschool , Drug Resistance, Multiple, Bacterial/genetics , Humans , Infant , Infant, Newborn , Middle Aged , Streptococcus pyogenes/genetics , United States/epidemiologyABSTRACT
A total of 986 isolates of Haemophilus influenzae from patients with respiratory tract infections in 45 United States medical centers were characterized during the winter of 2002-2003. beta-Lactamase production was noted with 26.2% of isolates; 14.6% were resistant to trimethoprim-sulfamethoxazole. Resistance to other relevant antimicrobial agents was extremely uncommon. In comparison to the results of four previous national surveys conducted since 1994, the prevalence of beta-lactamase production with this pathogen appears to be decreasing.
