Nationwide Surveillance and Molecular Characterization of Critically Drug-Resistant Gram-Negative Bacteria: Results of the Research University Network Thailand Study.

A large-scale surveillance is an important measure to monitor the regional spread of antimicrobial resistance. We prospectively studied the prevalence and molecular characteristics of clinically important Gram-negative bacilli, including Escherichia coli (EC), Klebsiella pneumoniae (KP), Acinetobacter baumannii complex (ABC), and Pseudomonas aeruginosa (PA) from blood, respiratory tract, urine, and sterile sites at 47 hospitals across Thailand. Among 187,619 isolates, 93,810 isolates (50.0%) were critically drug-resistant. Of which, 12,915 isolates (13.8%) were randomly selected for molecular characterization. EC was most commonly isolated from all specimens, except the respiratory tract in which ABC was predominant. Prevalence of extended-spectrum cephalosporin resistance (ESCR) was higher in EC (42.5%) than KP (32.0%), but carbapenem-resistant (CR)-KP (17.2%) was 4.5-fold higher than CR-EC (3.8%). A majority of ESCR-/CR-EC and KP carried blaCTX-M (64.6%-82.1%). blaNDM and blaOXA-48-like were the most prevalent carbapenemase genes in CR-EC/CR-KP (74.9%/52.9% and 22.4%/54.1%, respectively). Besides, 12.9%/23.0% of CR-EC/CR-KP co-carried blaNDM and blaOXA-48-like. Among ABC, 41.9% were extensively drug-resistant (XDR), and 35.7% were multidrug-resistant (MDR), while PA showed XDR/MDR at 6.3%/16.5%. A. baumannii (AB) was the most common species among ABC isolates. The major carbapenemase gene in MDR-AB/XDR-AB was blaOXA-23-like (85.8%/93.0%), which had much higher rates than other ABC species. blaIMP, blaVIM, blaOXA-40-like, and blaOXA-58-like were also detected in ABC at lower rates. The most common carbapenemase gene in MDR-/XDR-PA was blaIMP (29.0%/30.6%), followed by blaVIM (9.5%/25.3%). The findings reiterate an alarming situation of drug resistance that requires serious control measures.