MDR Salmonella enterica serovar Typhimurium ST34 carrying mcr-1 isolated from cases of bloodstream and intestinal infection in children in China. (3rd October 2019) - Luo, Qixia
Abstract: Objectives: Children are vulnerable to Salmonella infection due to their immature immune system. Cases of infection with mcr-1 -harbouring Salmonella in child inpatients have not been reported in China before. Methods: Salmonella isolates from gastroenteritis and bacteraemia were screened using primers targeting mcr-1. Complete genome sequences of mcr-1 -harbouring isolates were determined using the PacBio RS II platform. The transferability of mcr-1 -harbouring plasmids was verified by conjugation. Results: We investigated two mcr-1 -carrying polymyxin-resistant Salmonella enterica serovar Typhimurium ST34 isolates, S61394 and S44712, from bloodstream and intestinal Salmonella infection of two child inpatients, respectively. Both isolates were non-susceptible to commonly used antibiotics for children that compromised the success of clinical treatment and infection control. The mcr-1 -harbouring plasmids pLS61394-MCR and pLS44712-MCR (from S61394 and S44712, respectively) were both conjugative pHNSHP45-2-like IncHI2-type epidemic plasmids carrying multiple resistance genes. Compared with pHNSHP45-2, a ∼33 kb insertion region encoding Tn 7 transposition protein and heavy metal resistance proteins was identified in pLS61394-MCR, which might enhance adaptation of bacteria carrying this plasmid to various ecological niches. The phylogenetic tree of worldwide mcr -harbouring Salmonella indicated a host preference of mcr and a worldwide and cross-sectoral prevalence of the mcr -positive Salmonella ST34 clone. Conclusions: To our knowledge, for the first time we report completed whole genomes of mcr-1 -positive MDR Salmonella Typhimurium ST34 isolated from infected children in China, suggesting that improved surveillance is imperative for tackling the dissemination of mcr- harbouring MDR Salmonella Typhimurium ST34.