A sensitive and reduced-cost culture medium for recovery of <i>Clostridioides difficile</i> isolates with reduced fidaxomicin susceptibility from stool

ABSTRACT Emergence of resistance to fidaxomicin is a threat to current treatment algorithms for Clostridioides difficile infection (CDI), but current surveillance methods are labor-intensive and expensive. We tested the hypothesis that C. difficile Brucella agar (CDBA) media supplemented with 1 µg/mL fidaxomicin (CDBA-F1) would provide a sensitive, selective, and cost-effective method to screen stool specimens for C. difficile isolates with reduced fidaxomicin susceptibility (minimum inhibitory concentration &gt; 2 µg/mL). Clinical stool specimens testing positive for C. difficile ( N = 126) were plated on CDBA and CDBA-F1; C. difficile isolates recovered were tested for fidaxomicin susceptibility using agar dilution. The sensitivity of CDBA-F1 in comparison to CDBA was 100% for recovery of isolates with reduced fidaxomicin susceptibility (eight of eight detected). Breakthrough growth of stool microbiota was common, but most breakthrough organisms were easily distinguishable from C. difficile by colony morphology. Use of CDBA-F1 could provide a sensitive and selective media for detection of C. difficile isolates with reduced susceptibility while substantially reducing labor and supply costs. IMPORTANCE C. difficile isolates with reduced fidaxomicin susceptibility may emerge during CDI therapy and, in some cases, result in treatment failure. We report that supplementation of C. difficile selective media with fidaxomicin results in an effective, efficient, and reduced cost method to screen stool for isolates with reduced fidaxomicin susceptibility. Use of this approach could dramatically increase capacity to conduct surveillance for reduced fidaxomicin susceptibility in C. difficile .