647. Adoption of the updated fluoroquinolones breakpoints for Gram negative bacteria in clinical microbiology laboratories

BACKGROUND: Despite the multiple safety warnings related to fluoroquinolones (FQs) treatment, their use remains unavoidable in several occasions due to their broad spectrum of coverage including activity against multi-drug resistant glucose non-fermenting Gram-negative bacteria such as Pseudomonas spp., and high oral bioavailability. The Clinical and Laboratory Standards Institute (CLSI) has lowered the FQs minimal inhibitory concentrations (MICs) breakpoints for Salmonella spp. in 2012 and 2013, and for the Enterobacterales and P. aeruginosa in 2019. We aim to explore the number of hospitals that adopted the revised breakpoints. METHODS: We conducted a cross-sectional phone-based survey querying the 43 microbiology laboratories that serve 100% of the acute care and long-term hospitals in Connecticut to determine use of revised FQs MIC breakpoints for Gram-negative bacteria. RESULTS: Six laboratories refer antimicrobial susceptibility testing to another local hospital microbiology laboratory or to a national reference laboratory. Thus, we obtained information about the study question from a total of 37 microbiology laboratories. Eight laboratories (21.6%) were affiliated to university hospitals and 29 (78.4%) were community-based. Microscan Beckman coulter MicroScan was the most common antimicrobial susceptibility test method used in 15 (40.6%) microbiology laboratories followed by BioMérieux Vitek 2 in 13 (35.1%) laboratories. Four laboratories (10.8%) only adopted the revised CLSI FQs breakpoints for Enterobacterales, P. aeruginosa, and Salmonella spp, 5 (13.5%) implemented the revised breakpoints for Enterobacterales and P. aeruginosa but not for Salmonella spp., and 8 (21.6%) laboratories adopted the revised CLSI breakpoints for Salmonella spp. but not for Enterobacterales and P. aeruginosa. CONCLUSION: The use of outdated CLSI breakpoints for FQs against Gram-negative bacteria remains common in the microbiology laboratories. There is an urgent need to mitigate the impact of using the outdated FQs breakpoints and reporting false susceptibility to FQs. DISCLOSURES: All Authors: No reported disclosures