In Vitro Activities of Broad-Spectrum Cephalosporins against Nonmeningeal Isolates of Streptococcus pneumoniae : MIC Interpretation Using NCCLS M100-S12 Recommendations

Abstract

ABSTRACT Publication of the NCCLS M100-S12 document in January 2002 introduced ceftriaxone and cefotaxime MIC interpretative breakpoints of ≤1 μg/ml (susceptible), 2 μg/ml (intermediate), and ≥4 μg/ml (resistant) for nonmeningeal isolates of Streptococcus pneumoniae . To estimate the effect of these breakpoint changes on clinical laboratory susceptibility testing results, nonmeningeal pneumococcal isolate (blood and respiratory) data from The Surveillance Network Database-USA, an electronic surveillance database, for the years 1996 to 2000 were collated and studied. Of 9,863 nonmeningeal isolates tested against ceftriaxone, 82.7% were susceptible, 13.2% were intermediate, and 4.1% were resistant by the M100-S11 NCCLS breakpoints (2001); by M100-S12 breakpoints, 95.9% of the isolates were susceptible, 3.1% were intermediate, and 1.0% were resistant. Of 10,777 nonmeningeal isolates tested against cefotaxime, 79.2% were susceptible, 14.3% were intermediate, and 6.5% were resistant by M100-S11 breakpoints; by M100-S12 breakpoints, 93.5% were susceptible, 4.2% were intermediate, and 2.3% were resistant. Overall, the new M100-S12 ceftriaxone and cefotaxime interpretative breakpoints for nonmeningeal isolates of S. pneumoniae decreased the number of isolates interpreted as intermediate by 10% and as resistant by 3 to 4%.