Diversity of POM metallo-β-lactamase variants in the one Health context

Pseudomonas otitidis harbors an intrinsic subclass B3 metallo-β-lactamase (MBL), named POM, which contributes to reduced susceptibility to carbapenems. However, the diversity and functional implications of POM variants remain poorly studied. In this study, we investigated POM MBL in 65 strains from clinical, animal, and environmental origins from several countries, of which 19 Brazilian environmental strains were subjected to antimicrobial susceptibility testing. Sequence analysis identified the previously described POM-1 and POM-2, as well as 24 novel variants (POM-4 to POM-27). All variants displayed high amino acid identity (≥ 98.25%) and conserved key residues involved in zinc binding, indicating strong structural conservation. Whole-genome single nucleotide polymorphism analysis of P. otitidis genomes indicated that the distribution of POM variants was partly structured by strain phylogeny. Phenotypic comparisons were restricted to the 19 Brazilian environmental isolates and were descriptive only. These strains showed consistently elevated carbapenem minimum inhibitory concentrations (MIC), with meropenem and imipenem values ranging from 8 to 64 mg/L and 4 to 64 mg/L, respectively. Carbapenem MIC distributions overlapped across POM variants, with no clear genotype-phenotype pattern observed within this collection. Susceptibility to other antimicrobial classes was variable, although non-β-lactam agents generally retained activity. These findings demonstrate that POM enzymes constitute a highly conserved family of intrinsic MBL enzymes, while the relationship between POM sequence variation and carbapenem susceptibility remains unresolved within the limited phenotypic dataset. While variant-level identification has limited clinical utility, characterization of POM diversity provides insights into the evolution of intrinsic resistance.