Correlation between Identification of b-Lactamase Resistance Genes and Antimicrobial Susceptibility Profiles in Gram-Negative Bacteria: a Laboratory Data Analysis

We reported the frequency of resistance gene detection in Gram-negative blood culture isolates and correlated these findings with corresponding antibiograms. Data were obtained from 1045 isolates tested on the GenMark Dx ePlex Blood Culture Identification Gram-Negative Panels at the Mount Sinai Hospital Clinical Microbiology Laboratory in New York from March 2019 to February 2021. Susceptibilities were performed using Vitek 2 (bioMérieux Clinical Diagnostics) or Microscan (Beckman Coulter Inc.). bla_CTX-M was detected in 26.4% Klebsiella pneumoniae, 23.5% Escherichia coli, and 16.4% Proteus mirabilis isolates. As would be expected, both bla_CTX-M and bla_CTX-M negative isolates were likely to be susceptible to newer agents while bla_CTX-M positive isolates were more likely to be resistant to earlier generations of beta-lactam antibiotics. 3/204 bla_CTX-M-positive isolates were found to be ceftriaxone-susceptible. Conversely, 2.8% ceftriaxone nonsusceptible strains were negative for all b-lactamase genes on the ePlex BCID-GN panel, including bla_CTX-M. The prevalence of CTX-M-producing Enterobacterales remains high in the United States. A small number of bla_CTX-M-positive isolates were susceptible to ceftriaxone, and a small number of ceftriaxone nonsusceptible isolates were negative for bla_CTX-M. Further studies are needed to determine the optimal management when an isolate is phenotypically susceptible to ceftriaxone, but bla_CTX-M is detected. IMPORTANCE There is limited literature on corresponding results obtained from rapid molecular diagnostics with the antibiotic susceptibility profile. We reported a correlation between the results obtained from ePlex and the antibiograms against a large collection of Gram-negative bacteria. We reported that there can be a discrepancy in a small number of cases, but the clinical significance of that is unknown.