Macrolide-resistant Streptococcus pyogenes in the United States, 2002-2003.

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.

Antimicrobial resistance among Streptococcus pneumoniae in the United States: have we begun to turn the corner on resistance to certain antimicrobial classes?

BACKGROUND: Antimicrobial resistance has emerged as a major problem in Streptococcus pneumoniae in the United States during the past 15 years. This study was undertaken to elucidate the current scope and magnitude of this problem in the United States and to assess resistance trends since 1994-1995. METHODS: A total of 1817 S. pneumoniae isolates obtained from patients with community-acquired respiratory tract infections in 44 US medical centers were characterized during the winter of 2002-2003. The activity of 27 antimicrobial agents was assessed. In addition, selected isolates were examined for the presence of mutations in the quinolone-resistance determining regions (QRDRs) of parC and gyrA that resulted in diminished fluoroquinolone activity. The results of this survey were compared with the results of 4 previous surveys conducted in a similar manner since 1994-1995. RESULTS: Overall rates of resistance (defined as the rate of intermediate resistance plus the rate of resistance) were as follows: penicillin, 34.2%; ceftriaxone, 6.9%; erythromycin, 29.5%; clindamycin, 9.4%; tetracycline, 16.2%; and trimethoprim-sulfamethoxazole (TMP-SMX), 31.9%. No resistance was observed with vancomycin, linezolid, or telithromycin; 22.2% of isolates were multidrug resistant; 2.3% of isolates had ciprofloxacin MICs of >or=4.0 microg/mL. It was estimated that 21.9% of the isolates in this national collection had mutations in the QRDRs of parC and/or gyrA, with parC only mutations occurring most often (in 21% of all isolates). Trend analysis since 1994-1995 indicated that rates of resistance to beta -lactams, macrolides, tetracyclines, TMP-SMX, and multiple drugs have either plateaued or have begun to decrease. Conversely, fluoroquinolone resistance among S. pneumoniae is becoming more prevalent. CONCLUSION: It appears that, as fluoroquinolone resistance emerges among S. pneumoniae in the United States, resistance to other antimicrobial classes is becoming less common.

Decreasing prevalence of beta-lactamase production among respiratory tract isolates of Haemophilus influenzae in the United States.

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.

Caspofungin activity against clinical isolates of fluconazole-resistant Candida.

A total of 7,837 clinical isolates of Candida were tested against fluconazole, and 351 resistant (fluconazole MIC >/=64 micro g/ml) isolates were identified (4% of the total tested). All fluconazole-resistant isolates were inhibited by caspofungin at concentrations that can be exceeded by standard doses (MIC at which 90% of the isolates were inhibited, 1 micro g/ml; 99% of the MICs were