Tigecycline is a last-resort antimicrobial used to treat multidrug-resistant Gram-negative bacterial infections. One of the common antimicrobial resistance mechanisms is the efflux pump system composed of membrane protein complexes to excrete xenobiotic substrates. Recently, a novel gene cluster, tmexCD1-toprJ1, encoding the resistance–nodulation–cell division (RND) efflux pump was identified on plasmids in Klebsiella pneumoniae isolates in China. TMexCD1-TOprJ1 was found to be capable of excreting multiple antimicrobials, including tigecycline, which contributed to the strain's resistance. In this study, we identified K. pneumoniae isolates harbouring the tmexCD1-toprJ1 genes outside of China for the first time. Two tigecycline-resistant K. pneumoniae isolates belonging to ST273 by multilocus sequence typing were collected from different patients in a medical institution in Hanoi, Vietnam, in 2015. Whole-genome sequence analysis revealed that these isolates harboured a 288.0 kb tmexCD1-toprJ1–carrying plasmid with IncFIB and IncHI1B replicons. The tmexCD1-toprJ1 gene cluster was surrounded by several mobile gene elements, including IS26, and the plasmids had high sequence identity with that of K. pneumoniae isolated in China. Our finding suggests that the horizontal spread of tigecycline resistance mediated by tmexCD1-toprJ1–carrying plasmids has occurred in Vietnam and other countries, and raises concern about the further global dissemination.

Carbapenem-resistant Enterobacterales (CRE) represent a serious threat to public health due to the lack of treatment and high mortality. The rate of antimicrobial resistance of Enterobacterales isolates to major antimicrobials, including carbapenems, is much higher in Vietnam than in Western countries, but the reasons remain unknown due to the lack of genomic epidemiology research. A previous study suggested that carbapenem resistance genes, such as the carbapenemase gene blaNDM, spread via plasmids among Enterobacterales in Vietnam. In this study, we characterized blaNDM-carrying plasmids in Enterobacterales isolated in Vietnam, and identified several possible cases of horizontal transfer of plasmids both within and among species of bacteria. Twenty-five carbapenem-nonsusceptible isolates from a medical institution in Hanoi were sequenced on Illumina short-read sequencers, and 13 blaNDM-positive isolates, including isolates of Klebsiella pneumoniae, Escherichia coli, Citrobacter freundii, Morganella morganii, and Proteus mirabilis, were further sequenced on an Oxford Nanopore Technologies long-read sequencer to obtain complete plasmid sequences. Almost identical 73 kb IncFII(pSE11)::IncN hybrid plasmids carrying blaNDM-1 were found in a P. mirabilis isolate and an M. morganii isolate. A 112 kb IncFII(pRSB107)::IncN hybrid plasmid carrying blaNDM-1 in an E. coli isolate had partially identical sequences with a 39 kb IncR plasmid carrying blaNDM-1 and an 88 kb IncFII(pHN7A8)::IncN hybrid plasmid in a C. freundii isolate. 148–149 kb IncFIA(Hl1)::IncA/C2 plasmids and 75–76 kb IncFII(Yp) plasmids, both carrying blaNDM-1 were shared among three sequence type 11 (ST11) isolates and three ST395 isolates of K. pneumoniae, respectively. Most of the plasmids co-carried genes conferring resistance to clinically relevant antimicrobials, including third-generation cephalosporins, aminoglycosides, and fluoroquinolones, in addition to blaNDM-1. These results provide insight into the genetic basis of CRE in Vietnam, and could help control nosocomial infections.

Objective We investigated the impact of human immunodeficiency virus (HIV) infection and anti-retroviral therapy (ART) on the gut microbiota of children. Design This cross-sectional study investigated the gut microbiota of children with and without HIV. Methods We collected fecal samples from 59 children with HIV (29 treated with ART [ART(+)] and 30 without ART [HIV(+)]) and 20 children without HIV [HIV(–)] in Vietnam. We performed quantitative RT-PCR to detect 14 representative intestinal bacteria targeting 16S/23S rRNA molecules. We also collected the blood samples for immunological analyses. Results In spearman’s correlation analyses, no significant correlation between the number of dominant bacteria and age was found among children in the HIV(−) group. However, the number of sub-dominant bacteria, including Streptococcus, Enterococcus, and Enterobacteriaceae, positively correlated with age in the HIV(−) group, but not in the HIV(+) group. In the HIV(+) group, Clostridium coccoides group positively associated with the CD4+ cell count and its subsets. In the ART(+) group, Staphylococcus and C. perfringens positively correlated with CD4+ cells and their subsets and negatively with activated CD8+ cells. C. coccoides group and Bacteroides fragilis group were associated with regulatory T-cell counts. In multiple linear regression analyses, ART duration was independently associated with the number of C. perfringens, and Th17 cell count with the number of Staphylococcus in the ART(+) group. Conclusions HIV infection and ART may influence sub-dominant gut bacteria, directly or indirectly, in association with immune status in children with HIV.

24Carbapenem-resistant Enterobacteriaceae (CRE) represent a serious threat to public 25 health due to limited management of severe infections and high mortality. The rate of 26 resistance of Enterobacteriaceae isolates to major antimicrobials, including 27 carbapenems, is much higher in Vietnam than in Western countries, but the reasons 28 remain unknown due to the lack of genomic epidemiology research. A previous study 29 suggested that carbapenem resistance genes, such as the carbapenemase gene blaNDM-30 1, spread via plasmids among Enterobacteriaceae in Vietnam. In this study, we 31 performed detection and molecular characterization of blaNDM-1-carrying plasmids in CRE 32 isolated in Vietnam, and identified several possible cases of horizontal transfer of 33 plasmids both within and among species of bacteria. Twenty-five carbapenem-resistant 34 isolates from Enterobacteriaceae clinically isolated in a reference medical institution in 35Hanoi were sequenced on Illumina short-read sequencers, and 12 isolates harboring 36 blaNDM-1 were sequenced on an Oxford Nanopore Technologies long-read sequencer to 37 obtain complete plasmid sequences. Most of the plasmids co-carried genes conferring 38 resistance to clinically relevant antimicrobials, including third-generation cephalosporins, 39 aminoglycosides, and fluoroquinolones, in addition to blaNDM-1, leading to multidrug 40 resistance of their bacterial hosts. These results provide insight into the genetic basis of 41 CRE in Vietnam, and could help control nosocomial infections. 42 43