Evolutionary trajectories of beta-lactamase NDM and DLST cluster in Pseudomonas aeruginosa : finding the putative ancestor.

Pseudomonas aeruginosa has different antibiotic resistance pathways, such as broad-spectrum lactamases and metallo-β-lactamases (MBL), penicillin-binding protein (PBP) alteration, and active efflux pumps. Polymerase chain reaction (PCR) and sequencing methods were applied for double-locus sequence typing (DLST) and New Delhi metallo-β-lactamase (NDM) typing. We deduced the evolutionary pathways for DLST and NDM genes of P. aeruginosa using phylogenetic network. Among the analyzed isolates, 62.50% of the P. aeruginosa isolates were phenotypically carbapenem resistance (CARBR) isolates. Characterization of isolates revealed that the prevalence of bla NDM , bla VIM , bla IMP , undetermined carbapenemase, and MexAB-OprM were 27.5%, 2%, 2.5%, 12.5%, and 15%, respectively. The three largest clusters found were DLST t20-105, DLST t32-39, and DLST t32-52. The network phylogenic tree revealed that DLST t26-46 was a hypothetical ancestor for other DLSTs, and NDM-1 was as a hypothetical ancestor for NDMs. The combination of the NDM and DLST phylogenic trees revealed that DLST t32-39 and DLST tN2-N3 with NDM-4 potentially derived from DLST t26-46 along with NDM-1. Similarly, DLST t5-91 with NDM-5 diversified from DLST tN2-N3 with NDM-4. This is the first study in which DLST and NDM evolutionary routes were performed to investigate the origin of P. aeruginosa isolates. Our study showed that the utilization of medical equipment common to two centers, staff members common to two centers, limitations in treatment options, and prescription of unnecessary high levels of meropenem are the main agents that generate new types of resistant bacteria and spread resistance among hospitals.