More than just the gene: investigating expression using a non-native plasmid and host and its impact on resistance conferred by β-lactamase OXA-58 isolated from a hospital wastewater microbiome

With the escalation of hospital-acquired infections by multidrug resistant bacteria, understanding antibiotic resistance is of paramount importance. This study focuses on the β-lactamase gene, bla_OXA-58, an important resistance determinant identified in a patient-facing hospital wastewater system. This study aimed to characterize the behaviour of the OXA-58 enzyme when expressed using a non-native plasmid and expression host. bla_OXA-58 was cloned using a pET28a(+)/Escherichia coli BL21(DE3) expression system. Nitrocefin hydrolysis and antimicrobial susceptibility of OXA-58-producing cells were assessed against penicillin G, ampicillin, meropenem, and amoxicillin. bla_OXA-58 conferred resistance to amoxicillin, penicillin G, and ampicillin, but not to meropenem. This was unexpected given OXA-58’s annotation as a carbapenemase. The presence of meropenem also reduced nitrocefin hydrolysis, suggesting it acts as a competitive inhibitor of the OXA-58 enzyme. This study elucidates the phenotypic resistance conferred by an antimicrobial resistance gene (ARG) obtained from a clinically relevant setting and reveals that successful functional expression of ARGs is multifaceted. This study challenges the reliability of predicting antimicrobial resistance based solely on gene sequence alone, and serves as a reminder of the intricate interplay between genetics and structural factors in understanding resistance profiles across different host environments.