Development of disk diffusion susceptibility test methods for <i>Aerococcus</i> spp. and updates to Clinical and Laboratory Standards Institute MIC breakpoints

<i>Aerococcus</i> species are an increasingly recognized cause of urinary tract infections and may cause serious infections, including endocarditis. Antimicrobial susceptibility testing (AST) is required for the management of these infections, as species within the genus display resistance to various antimicrobial agents. This study describes the data that informed updates to the Clinical and Laboratory Standards Institute M45 guideline for AST of fastidious or infrequently isolated bacteria. We describe the introduction of new ampicillin and nitrofurantoin breakpoints, updated MIC breakpoints for penicillin, and disk diffusion correlates for penicillin, ampicillin, ciprofloxacin, levofloxacin, nitrofurantoin, and tetracycline.