In Vitro Susceptibility Testing of Fluoroquinolone Activity Against Salmonella: Recent Changes to CLSI Standards

Fluoroquinolone (FQ) resistance in Salmonella enterica is a significant clinical concern. Recognition of resistance by the clinical laboratory is complicated by the multiple FQ resistance mechanisms found in Salmonella. The Clinical Laboratory Standards Institute (CLSI) recently addressed this issue by revising the ciprofloxacin break points for Salmonella species. It is critical for clinicians and laboratory workers to be aware of the multiple technical issues surrounding these revised break points. In this article, we review FQ resistance mechanisms in Salmonella, their clinical significance, and data supporting the revised ciprofloxacin break points. We encourage clinical laboratories to adopt the revised CLSI ciprofloxacin break points for all Salmonella isolates in which susceptibility testing is indicated and discuss the technical issues for laboratories using commercial antimicrobial susceptibility systems.