[Genetic diversity analysis of oxacillinase in 241 clinical isolates of Pseudomonas aeruginosa].

Objective: To analyze the carriage status, subtype distribution and flanking gene sequence characteristics of oxacillinases (OXA enzyme) in 241 clinical strains of Pseudomonas aeruginosa, and assess their roles in the drug resistance of Pseudomonas aeruginosa and ability to horizontally transfer across species. Methods: Clinical P. aeruginosa isolates were collected from four hospitals in Sanya, Tangshan, Zhangjiakou, and Beijing. The prevalence of oxacillinases and their flanking gene sequences was analyzed by whole-genome sequencing (NGS) and bioinformatic approaches. Results: A total of 241 isolates of P. aeruginosa were gathered, and 35 bla_OXA subtypes were identified through screening of 252 bla_OXA genes. These genes were classified into three subfamilies: bla_OXA-50-like (241, 95.6%), bla_OXA-1-like (9, 3.6%) and bla_OXA-10-like (2, 0.8%). Among these, 11 subtypes (11, 31.4%) were novel bla_OXA subtypes. Nine of these belonged to the bla_OXA-50-like subfamily and were designated as bla_OXA-1244, bla_OXA-1245, bla_OXA-1246, bla_OXA-1250, bla_OXA-1252, bla_OXA-1253, bla_OXA-1254, bla_OXA-1255, and bla_OXA-1256. The remaining two belonged to the bla_OXA-10-like subfamily and were named bla_OXA-1247 and bla_OXA-1248. Compared to the amino acid sequence of OXA-10, the newly identified subtype OXA-1247 exhibited a mutation at position 117, where a valine was replaced by a leucine. This change was thought to improve the enzyme's ability to hydrolyze carbapenems. In the analysis of the flanking sequences of the bla_OXA genes, Class I integrons were identified in four bacterial strains. The variable regions of these integrons carried three distinct patterns of resistance gene cassettes: aac(6')-Ib-bla_OXA-1247-ant(3'')-Ia, aac(6')-Ib-bla_OXA-1248 and aac(6')-Ib-bla_IMP-45-bla_OXA-1-catB3. Among these, the strain BJ2326 carried a class I integron that was connected to the downstream ISCR1 element to form a composite class I integron structure, additionally carrying the resistance gene bla_PER-1. Out of the 223 non-wild-type P. aeruginosa strains, 127 strains exhibited non-wild-type profiles to the four beta-lactam antibiotics MEM, CAZ, FEP, and TZP, with the combination of MEM+CAZ+FEP being the most prevalent, representing 57.0% of the total. Conclusions: The bla_OXA genes in 241 clinical P. aeruginosa strains showed diversity. Some bla_OXA genes had a co-transfer risk with the metallo-β-lactamase resistance gene blaIMP-45. Among the 11 newly discovered bla_OXA subtypes, the new subtype OXA-1247 may have carbapenemase activity and potential for horizontal transfer.