Comparative activity of gatifloxacin and other antibiotics against 4009 clinical isolates of Streptococcus pneumoniae in the United States during 1999-2000.

The susceptibility of 4009 recent clinical isolates of Streptococcus pneumoniae to gatifloxacin, levofloxacin, ciprofloxacin, penicillin, ceftriaxone and azithromycin was determined. Overall rates of susceptibility to these agents were 99.4, 98.7, 71.2, 55.2, 80.9, and 71.3%, respectively. Resistance to all tested agents was associated with penicillin resistance. Of penicillin nonsusceptible isolates, 36% were resistant. Resistance to the fluoroquinolones was unusual and gatifloxacin generally appeared to be four-fold more active than levofloxacin or ciprofloxacin. Multidrug resistant S. pneumoniae accounted for 6.2% of this sample. The lowest rate of susceptibility to non-fluoroquinolone antibiotics was observed in isolates from the South region of the United States, which appeared to be explained by both the proportion of and the inherently higher MICs of certain types of isolates.