Accuracy of broth microdilution and E test methods for detecting chloramphenicol acetyl transferase mediated resistance in Streptococcus pneumoniae: Geographic variations in the prevalence of resistance in The SENTRY Antimicrobial Surveillance Program (1999)

Abstract

High antimicrobial resistance rates in Streptococcus pneumoniae has caused a need for alternative therapies. Chloramphenicol is currently being reconsidered as an empiric treatment for respiratory tract infections particularly in developing countries. In this study, we assessed the ability of the reference broth microdilution and Etest (AB BIODISK, Solna, Sweden) methods to detect chloramphenicol resistance among pneumococci as compared to the chloramphenicol acetyltransferase (CAT) assay. In the 1999 SENTRY Antimicrobial Surveillance Program, 1671 S. pneumoniae strains from respiratory tract infections were collected from 49 participants located in the Americas and Europe. The rates of penicillin and macrolide non-susceptibility were 15.6–41.3 and 12.4–26.8%, respectively. All chloramphenicol-resistant strains were CAT assay positive ( n = 154; 9.2% of isolates) with highest resistance rates in Europe (12.7%; range among sites, 0.0–38.5%) and the United States (10.6%; range, 0.0–25.6%). Etest MICs correlated with reference results and the current breakpoint for chloramphenicol resistance (≥8 μg/mL) remains valid for S. pneumoniae and Haemophilus influenzae (eight strains tested). CAT-mediated resistances dominate among chloramphenicol-resistant S. pneumoniae, and marked geographic variations in susceptibility were discovered.