Antimicrobial Susceptibility among
Mark E. Jones, PhD, Nina P. Brown, MSc, Deborah C.
Draghi, BSc, Clyde Thornsberry, PhD, Daniel F.
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.