Clinical characteristics of patients with bacteraemia due to the emergence of mcr-1-harbouring Enterobacteriaceae in humans and pigs in Taiwan

•Rates of mcr-1+ bacteraemic isolates were 0.9%, 0.4% and 0.9% for E. coli, K. pneumoniae and Salmonella spp., respectively.•Among 16 E. coli isolates collected from 16 pigs, 12 (75.0%) were mcr-1+.•Pulsotypes of the 6 human mcr-1+ E. coli were different from each other and also varied from those of the porcine isolates.•Among 10 patients with bacteraemia caused by mcr-1+ isolates, 5 each were community-acquired and hospital-acquired.•Sepsis-related mortality occurred in four patients (40.0%) with bacteraemia. This nationwide surveillance was conducted in 2017 to investigate the prevalence and clinical characteristics of patients with bacteraemia due to mcr-1-harbouring Enterobacteriaceae as well as the presence of mcr-1-harbouring Escherichia coli in pigs. Non-duplicate, consecutive bacterial isolates were collected from patients treated at 16 hospitals in Taiwan. All E. coli (n = 686) and Klebsiella pneumoniae (n = 673) isolates from humans were obtained from patients with bacteraemia; for Salmonella spp. isolates (n = 221), 52.5% were obtained from blood samples and 26.2% from stool samples. The rates of mcr-1-harbouring bacteraemic isolates were 0.9% (6/686), 0.4% (3/673) and 0.9% (1/116) for E. coli, K. pneumoniae and Salmonella spp., respectively. Among the 16 E. coli isolates collected from 16 pigs, 12 (75.0%) were positive for mcr-1. Two mcr-1-positive K. pneumoniae isolates, one possessing K. pneumoniae carbapenemase (KPC) only and the other possessing both KPC and OXA-48, exhibited high-level resistance to carbapenems [minimum inhibitory concentrations (MICs) ≥64 mg/L]. The 12 mcr-1-positive E. coli isolates from pigs were all susceptible to carbapenems. Pulsotypes of the six human mcr-1-positive E. coli isolates were different from each other and also varied from those of the porcine isolates. Among the ten patients with bacteraemia caused by mcr-1-harbouring isolates, five had community-acquired infections and five had hospital-acquired infections. Sepsis-related mortality occurred in four patients (40.0%) with bacteraemia. These findings indicate the importance of regular screening for the presence of mcr-1 in Enterobacteriaceae in humans and animals to prevent the spread of infection in hospitals and the community.