We performed multicentre surveillance of the antimicrobial susceptibility of clinically important Gram-negative bacteria (GNB) from 16 hospitals in Taiwan. Escherichia coli (n=398), Klebsiella pneumoniae (n=346), Pseudomonas aeruginosa (n=252) and Acinetobacter baumannii complex (n=188) bloodstream isolates, non-typhoid Salmonella (NTS; n=230) and Shigella species (n=18) from various sources were collected. Antibiotic minimum inhibitory concentrations (MICs) were determined using the broth microdilution method. Alleles encoding K. pneumoniae carbapenemases (KPCs), New Delhi metallo-β-lactamases (NDMs), Verona integron-encoded metallo-β-lactamase (VIM), OXA-48-like carbapenemase (OXA-48) and mcr-1-5 genes were detected by molecular methods. The carbapenem non-susceptible (NS) rates were 2.8%, 9.0%, 0.4%, 0%, 10.3% and 48.8% for E. coli, K. pneumoniae, NTS, Shigella, P. aeruginosa and A. baumannii complex, respectively. For carbapenemases, one (0.3%) E. coli isolate harboured blaNDM-1 alleles. Fifteen (4.3%), two (0.6%) and two (0.6%) K. pneumoniae isolates contained blaKPC, blaOXA-48 and blaVIM, respectively. Two (0.5%) E. coli and fourteen (6.4%) K. pneumoniae isolates were non-wild type according to the MIC of colistin. Among Enterobacteriaceae with a colistin MIC ≥2 mg/L, mcr-1 was detected in one E. coli, two K. pneumoniae and three Salmonella species. All three mcr-1-positive Salmonella species were collected from community-acquired infections, and none of the six mcr-1-positive Enterobacteriaceae were carbapenem-resistant. In conclusion, carbapenem resistance increased among clinically important GNBs, especially among hospital-acquired infections. The blaKPC, especially the blaKPC-2 variant, was detected in approximately half of the carbapenem-resistant K. pneumoniae isolates in Taiwan. Although colistin still had low resistance rates among Enterobacteriaceae, the mcr-1 from different species raises the concern of potential dissemination.
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