Molecular epidemiology of carbapenemase-producing Enterobacteriaceae from humans and animals

Abstract

Carbapenemase-producing Enterobacteriaceae (CPE)is imposing a severe threat to public health. Mortality from infections caused by invasive CPE has reached up to approximately 40% [105].Previous works have demonstrated its wide distributions worldwide, and the major transmission mechanisms attributed to clonal dissemination vertically, and horizontal transmission of epidemic plasmids. Attempts have been made to develop optimized phenotypic methods for rapid detection of CPE. Optional therapeutic treatment with combination of other antibiotics such as colistin and fosfomycin came into view in combatting CPE infections. However, despite the large amount of studies investigating the epidemiology of CPE in humans, previous findings failed to elucidate its potential transmission in the human-animal circulation. Updated and deeper investigations are urged to decipher the situation. In this study, we investigated the epidemiology of CPE on 1,812 strains from humans and animals or on-bench constructed during 2005 to 2017. Starting from the validation of CPE detection methods, we found that the CLSI protocol of Carba NP showed optimistic performance and acceptable inter-and intra-observer variations through evaluation with 548 clinical carbapenem-resistant isolates. The CLSI Carba NP is suitable for clinical usage in Hong Kong. Nonetheless, slight modifications of the CLSI protocol with the application of strips (the Strip Carba NP) gave even better performance, with higher sensitivity and a shorter duration of examination.

Secondly, we identified an epidemic IncN ST7 plasmid mediating the transmission of blaIMP-4among 29 IMP-producing isolates collected during 2010-2013, fulfilling the current research gap in the epidemiology of IMP-carbapenemase. The stability and minimal fitness cost of this plasmid promoted the predominant dissemination of blaIMP among populations.

Thirdly, we found that the dissemination of blaNDM-5is mediated by IncX3 plasmids in Enterobacteriaceae isolates from both humans and animals. In our previous works, the IncX3 plasmids were found to be an epidemic vehicle in NDM’s dissemination in humans[174]. The expansion of carbapenemase is no longer a curse limited to the human populaion, but has moved into the human-animal circulation. In the fourth, we found that circulation of the plasmid-mediated colistin resistance gene mcr-1has penetrated into human communities with the transmission of plasmids. Through in vitro transposition experiments, the mobilization mechanism of mcr-1byISApl1was characterized as a one-end transposition, which can be promoted by application of colistin and a lower growth temperature at 25°C. Lastly, this study identified a significant carriage rate of fosfomycin resistance (26%) in clinical CPE isolates. Similar to colistin, fosfomycin is one of the “last resorts of choices” combatting CPE infection. The high proportion of multidrug resistance in fosfomycin-resistant CPE indicates an even further deteriorated situation. The co-habitat of fosC2 and blaIMP-34in the same integron in plasmid pIMP-HB623 emphasized the importance of plasmids and mobile genetic elements in dissemination of resistance genes.