Plasmid-Borne AFM Alleles in Pseudomonas aeruginosa Clinical Isolates from China.

Carbapenem-resistant Pseudomonas aeruginosa (CRPA) is a pathogen of global concern due to the fact that therapeutic drugs are limited. Metallo-β-lactamase (MBL)-producing P. aeruginosa has become a critical part of CRPA. Alcaligenes faecalis metallo-β-lactamase (AFM) is a newly identified subclass B1b MBL. In this study, 487 P. aeruginosa strains isolated from patients and the environment in an intensive care unit were screened for AFM alleles. Five AFM-producing strains were identified, including four AFM-2-producing strains (ST262) and one AFM-4-producing strain (ST671). AFM-2-producing strains were isolated from rectal and throat swabs, and AFM-4-producing strains were isolated from the water sink. The bla AFM-2 carrying plasmids belonged to the IncP-2 type, while the bla AFM-4 carrying plasmid pAR19438 was a pSTY-like megaplasmid. Plasmid pAR19438 was acquired bla AFM-4 by the integration of the Tn 1403 -like transposon. All bla AFM genes were embedded in an IS CR29 - bla AFM unit core module flanked by class 1 integrons. The core module of bla AFM-2 was IS CR29 -Δ groL - bla AFM-2 - ble MBL -Δ trpF -ΔIS CR , while the core module of bla AFM-4 was IS CR29 -Δ groL - bla AFM-2 - ble MBL -Δ trpF -IS CR - msrB - msrA - yfcG - corA -ΔIS CR . The flanking sequences of IS CR29 - bla AFM units also differed. The expression of AFM-2 and AFM-4 in DH5α and PAO1 illustrated the same effect for the evaluation of the MICs of β-lactams, except for aztreonam. Identification of AFM-4 underscores that the quick spread and emerging development of mutants of MBLs require continuous surveillance in P. aeruginosa. IMPORTANCE Acquiring metallo-β-lactamase genes is one of the important carbapenem resistance mechanisms of P. aeruginosa. Alcaligenes faecalis metallo-β-lactamase is a newly identified metallo-β-lactamase, the prevalence and genetic context of which need to be explored. In this study, we identified AFM-producing P. aeruginosa strains among clinical isolates and found a new mutant of AFM, AFM-4. The bla AFM-4 carrying plasmid pAR19438 was a pSTY-like megaplasmid, unlike the plasmids encoding other bla AFM alleles. The genetic context of bla AFM-4 was also different. However, AFM-2 and AFM-4 had the same impacts on antibiotic susceptibility. The presence and transmission of AFM alleles in P. aeruginosa pose a challenge to clinical practice.