In vitro activity of cefditoren and other antimicrobial agents against 288 Streptococcus pneumoniae and 220 Haemophilus influenzae clinical strains isolated in Zaragoza, Spain

Abstract In vitro cefditoren antimicrobial activity was tested against 288 Streptococcus pneumoniae and 220 Haemophilus influenzae clinical strains isolated in our hospital from January 2005 to May 2006 by agar dilution and broth microdilution method, respectively. MICs were also determined for 13 and 10 comparison drugs, respectively. The pneumococci tested comprised 113 (39.2%) penicillin susceptible, 91 (31.6%) penicillin intermediate, and 84 (29.2%) penicillin resistant. Cefditoren was the most active drug on the basis of the MICs (MIC 90  = 0.5 μg/mL), followed by ceftriaxone and levofloxacin (MIC 90 = 1 μg/mL). Cefditoren MICs ranged from 0.25 to 1 μg/mL for ceftriaxone-resistant isolates, with a modal MIC of 0.5 μg/mL and an MIC 90 of 1.0 μg/mL. No S. pneumoniae isolates evaluated in this study showed MICs to cefditoren higher than 1 μg/mL (MIC range, ≤0.015 to 1 μg/mL). Against penicillin-resistant pneumococci, the rank order of intrinsic activity (MIC 90 , μg/mL) was cefditoren (0.5) H. influenzae , 42 (19.09%) produced a β-lactamase (Hi β+) and 3 (1.1%) were β-lactamase (Hi β-) negative but have reduced susceptibility to ampicillin (BLNAR). The most active drugs on the basis of MICs were cefditoren and levofloxacin, showing MIC 50 and MIC 90 values of 0.015/0.06 μg/mL. Cefditoren at concentration of 0.06 μg/mL inhibited all 3 BLNAR (ampicillin MICs >4 μg/mL). Against H. influenzae (Hi β+), the rank order of intrinsic activity (MIC 90 , μg/mL) was cefditoren (0.03) 8.0).