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Antimicrobial Susceptibility among Streptococcus pneumoniae

Mark E. Jones, PhD, Nina P. Brown, MSc, Deborah C. Draghi, BSc, Clyde Thornsberry, PhD, Daniel F. Sahm, PhD
Eurofins Antiinfective Services Inc., Herndon, VA, USA

Levofloxacin represents the first of the expanded spectrum fluoroquinolones with potent activity against major respiratory pathogens including Streptococcus pneumoniae. The GLOBAL Surveillance study is a longitudinal study which prospectively collects respiratory pathogens from East Asia, South East Asia, Europe, Latin America, and South Africa. During the 2005/2006 respiratory season 2,725 S. pneumoniae were collected and re-identified and their susceptibility tested to levofloxacin and comparators using CLSI standards in a central laboratory. Penicillin, macrolide, and trimethoprim-sulfamethoxazole resistance was detected in every country. Asian countries had the highest rates of resistance which frequently accounted for > 50% of all isolates. Worldwide, levofloxacin retained potent in vitro activity, with an overall rate of resistance among S. pneumoniae of <1% in most countries. In Indonesia, South Africa, Thailand, and the UK, no levofloxacin resistance was detected. In Hong Kong, 9.4% of S. pneumoniae were levofloxacin-resistant, a reduction from the prevalence recorded in previous studies.
Levofloxacin demonstrated MIC90s of 1 µg/mL in all countries. The MIC distributions show that the majority of isolates have MICs of 0.5 or 1 µg/mL with few or no isolates at MIC 2 µg/mL (CLSI breakpoint of 4 µg/mL). Multidrug resistance (MDR), defined as concurrent resistance to 3 2 antimicrobial agents (penicillin, cefuroxime, azithromycin, and trimethoprim-sulfamethoxazole) was present in 940 (34.5%) isolates (an increase of 7.5% compared with the 2003 study). Resistance to penicillin, azithromycin, cefuroxime and trimethoprim-sulfamethoxazole was the most common MDR phenotype present in 15.2% of all isolates. Levofloxacin non-susceptibility was rarely associated with MDR phenotypes, and overall, 97.1% were levofloxacin-susceptible. Also, 95% of the most common resistant phenotype (resistant to penicillin, azithromycin, Trimethoprim-sulfamethoxazole, and cefuroxime) were levofloxacin-susceptible.

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