Detecting and Reporting Extended Spectrum Beta-Lactamases Producers: Evaluation of Three Approaches and the Clinical Impact

Abstract Introduction/Objective Since the COVID-19 pandemic, bacteria producing extended spectrum beta-lactamases (ESBLs) have increased >30%. Laboratories can perform phenotypic microbroth dilution or molecular approaches to identify ESBL producers. However, the gold standard is a laborious double disc synergy test. We evaluated the concordance among the three approaches, the clinical impact, and justification of reporting ESBL producers. Methods/Case Report Seventy-eight ESBL producers identified by microbroth dilution (MicroScan WalkAway, Beckman Coulter, Brea, California, USA) or detection of blaCTX-M gene from blood cultures (BCID2 Panel, BioFire, Biomerieux, Salt Lake City, Utah, USA) were tested using double disc synergy test retrospectively. Concordance among the methods evaluated. Discordant cases were reviewed with subsequent patient chart review. Results (if a Case Study enter NA) Tested isolates included E. coli (n=44, 57%), K. pneumoniae (n=19, 24%), K. oxytoca (n=7, 9%), and P. mirabilis (n=8, 10%). Concordance between microbroth dilution and disk diffusion was 86% (67/78). For isolates with genotypic testing (n=16), concordance with microbroth dilution and disk diffusion was 93% and 88%, respectively. Overall concordance was 88%. There were 12 isolates (E. coli:8, P. mirabilis: 2, and K. pneumoniae:2) with discordant results from one method. The susceptibility profile of discordant isolates revealed resistance to ceftriaxone or ceftazidime (11/12), penicillin (11/12), and aztreonam (6/12); 10/12 isolates were resistant to at least 2 groups of these antibiotics, a phenotype of ESBL producers. Clinical teams acknowledged presence of ESBLs in 83% (10/12) of cases and 58% (7/12) warranted treatment with meropenem or combinational therapy. Infection prevention implemented contact isolate procedures in all cases. Conclusion Our current in-house methods (e.g., microbroth dilution and genotypic testing) are still justified for ESBL testing to optimize patient care in a timely fashion. In the minor cases with discordant results, clinical care was unaffected. Laboratory workflow changes need to take laboratory efficiency, patient outcomes, and actionable clinical changes into consideration.