Molecular characteristics of carbapenem-resistant gram-negative bacteria in southern China

A total of 368 nonreplicate gram-negative bacteria with resistance to imipenem or meropenem were collected to search for carbapenemase genes, class 1 integrons, and insertion sequence with common region 1 (ISCR1). The carbapenemase genes blaIMP-4, blaKPC-2, and blaNDM-1 were found in two Enterobacteriaceae and seven Pseudomonas aeruginosa isolates, nine Klebsiella pneumoniae isolates, and seven Enterobacteriaceae and two Acinetobacter spp. isolates. The class D OXA-type carbapenemase genes blaOXA-23-like, blaOXA-24-like, blaOXA-58, and blaOXA-51-like were detected in 59 (34.9%), 2 (1.2%), 16 (9.5%), and 126 (74.6%) Acinetobacter strains. This is the first description of blaNDM-1 in Enterobacter hormaechei and Acinetobacter genomic species 13TU. Of the integrase-positive strains, 135 (90.0%) Acinetobacter spp., 22 (61.1%) P. aeruginosa, and 14 (100%) Enterobacteriaceae isolates were identified by five, ten, and four different gene cassette arrays, respectively. Three novel gene cassette arrays aadB-aadA1, dfrA25, and dfrA16-aadA2 were reported for the first time in some species. Of the ISCR1-positive strains, the nonfermentative strains (102 Acinetobacter spp. and 13 P. aeruginosa. isolates) contained the same arrangement blaPER-1-putative glutathione-S-transferase-novel type ABC transporter, and three Enterobacteriaceae isolates harbored three different arrangements. Four distinct complex class 1 integron structures were observed. The complex class 1 integron detected in New Delhi, metallo-β-lactamase (NDM-1)-producing E. hormaechei, was found to coexist in the NDM-1-carrying plasmid. Our results suggested that we should pay more attention to the strict implementation of infection control measures and active antibiotic resistance surveillance to avoid the rapid spread or outbreak of carbapenemase-producing gram-negative bacteria.