Diversity of bla_POM in carbapenem-resistant opportunistic pathogenic Pseudomonas otitidis in municipal wastewater

Metallo-beta-lactamases (MBLs) encoding carbapenem resistance in wastewater are a well-known serious threat to human health. Twelve Pseudomonas otitidis isolates obtained from a municipal wastewater treatment plant (WWTP) in Hawaii were found to possess a subclass B3 MBL - POM ( P. otitidis beta MBL), with a minimum inhibition concentration (MIC) range of 8-16 mg/L. The unrooted neighbor-joining phylogenetic tree showed that these bla(POM) genes isolated in wastewater samples (n = 12) were distinctly different from other reference genes isolated from clinical, freshwater, animal, and soil samples except for isolates MR7, MR8, and MR11. MR7, MR8, and MR11 were found to have 4, 3, and 3 amino acid substitutions when compared to the type strain MC10330(T) and were closely clustered to the clinical reference genes. The meropenem hydrolysis experiment showed that isolates with multiple amino acid substitutions completely hydrolyzed 64 mg/L of meropenem in 7 h. The emergence of the opportunistic pathogen P. otitidis chromosomally encoding blaPOM in the treated municipal wastewater is an alarming call for the spread of this MBL in the environment. Further studies are required to understand the mechanism and regulation of this carbapenem-resistant beta-lactamase in order to fill in the knowledge gap.