The impact of the coronavirus disease (COVID-19) pandemic on antimicrobial resistance (AMR) is a major concern. To compare the number of patients and isolation rate of antimicrobial-resistant bacteria before and after the beginning of the COVID-19 pandemic using the comprehensive national surveillance data. We utilized comprehensive surveillance data, collected in the Japan Nosocomial Infections Surveillance programme, which included a total of 16.7 million samples of 5.9 million tested patients from >1300 hospitals. We compared the number of patients and isolation rate of five bacteria between 2019 and 2020, including antimicrobial-susceptible and -resistant bacteria of Staphylococcus aureus, Streptococcus pneumoniae, Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa. The number of patients and isolation rate of S. aureus and meticillin-resistant S. aureus decreased slightly; those of S. pneumoniae and penicillin-resistant S. pneumoniae decreased by 60%; and those of third-generation cephalosporin-resistant K. pneumoniae increased. The isolation rate of the remaining bacteria apparently increased, although the number of patients decreased. This was due to a substantial decrease in the total number of tested patients (the denominator of the isolation rate), which was larger than that of the number of patients (the numerator of the isolation rate). Consistent results were obtained when the same data were re-aggregated using the procedure of the World Health Organization Global Antimicrobial Resistance Surveillance System, demonstrating the general importance of this problem. Surveillance data during the COVID-19 pandemic must be carefully interpreted based on examination of the numerator, denominator and background factors that affect the denominator.

Japan is a country with an approximate 10% prevalence rate of carbapenem-resistant Pseudomonas aeruginosa (CRPA). Currently, a comprehensive overview of the genotype and phenotype patterns of CRPA in Japan is lacking. Herein, we conducted genome sequencing and quantitative antimicrobial susceptibility testing for 382 meropenem-resistant CRPA isolates that were collected from 78 hospitals across Japan from 2019 to 2020. CRPA exhibited susceptibility rates of 52.9%, 26.4%, and 88.0% against piperacillin–tazobactam, ciprofloxacin, and amikacin, respectively, whereas 27.7% of CRPA isolates was classified as difficult-to-treat resistance P. aeruginosa . Of the 148 sequence types detected, ST274 (9.7%) was predominant, followed by ST235 (7.6%). The proportion of urine isolates in ST235 was higher than that in other STs ( P = 0.0056, χ ² test). Only 4.1% of CRPA isolates carried the carbapenemase genes: bla _GES (2) and bla _IMP (13). One ST235 isolate carried the novel bla _IMP variant bla _IMP-98 in the chromosome. Regarding chromosomal mutations, 87.1% of CRPA isolates possessed inactivating or other resistance mutations in oprD , and 28.8% showed mutations in the regulatory genes ( mexR , nalC , and nalD ) for the MexAB-OprM efflux pump. Additionally, 4.7% of CRPA isolates carried a resistance mutation in the PBP3-encoding gene ftsI . The findings from this study and other surveillance studies collectively demonstrate that CRPA exhibits marked genetic diversity and that its multidrug resistance in Japan is less prevailed than in other regions. This study contributes a valuable data set that addresses a gap in genotype/phenotype information regarding CRPA in the Asia–Pacific region, where the epidemiological background markedly differs between regions.

The increasing incidence of candidemia and the emergence of drug-resistant Candida species are major concerns worldwide. Therefore, long-term surveillance studies are required. Here, we provide one of the largest longitudinal overviews of the trends in the prevalence of Candida species using national data of 57 001 candidemia isolates obtained from > 2000 hospitals for the 2010–2019 period in the Japan Nosocomial Infections Surveillance database. The proportion of Candida species, except Candida krusei and Candida guilliermondii, was almost the same during the study period. The proportion of C. guilliermondii surpassed that of C. krusei in 2014. The incidence of candidemia due to C. albicans (P < 0.0001), C. parapsilosis (P = 0.0002), and C. tropicalis (P < 0.0001) have decreased significantly over this period. Azole susceptibility of C. tropicalis was low, with 17.8% of isolates resistant to fluconazole and 13.5% resistant to voriconazole. The micafungin susceptibility of C. glabrata was low, with 8.0% of isolates showing resistance. The resistance rate of C. krusei toward amphotericin B fluctuated considerably (between 3.2% and 35.7%) over this period. The incidence rate of candidemia caused by C. parapsilosis and C. guilliermondii in hospitals responsible for bone marrow transplantation was significantly higher than that in other hospitals. Overall, our study suggests that in Japan, the species distribution of Candida was almost the same in this period and similar to that reported in North America and Europe. A relatively high resistance to azoles and micafungin was observed in C. glabrata, C. tropicalis, and C. krusei isolates, which require continued surveillance. This study verifies that the proportion of Candida species in Japan was almost the same from 2010–2019. A relatively higher resistance to azoles and micafungin was observed for C. glabrata, C. tropicalis, and C. krusei isolates.

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 bla_NDM, spread via plasmids among Enterobacterales in Vietnam. In this study, we characterized bla_NDM-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 bla_NDM-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 bla_NDM-1 were found in a P. mirabilis isolate and an M. morganii isolate. A 112 kb IncFII(pRSB107)::IncN hybrid plasmid carrying bla_NDM-1 in an E. coli isolate had partially identical sequences with a 39 kb IncR plasmid carrying bla_NDM-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 bla_NDM-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 bla_NDM-1. These results provide insight into the genetic basis of CRE in Vietnam, and could help control nosocomial infections.

Tigecycline resistance mediated by the mobile tigecycline-inactivating enzyme gene tet(X) in Gram-negative bacteria is an emerging concern for global public health. However, limited information is available on the distribution of tet(X) in the natural environment. In this study, we investigated the presence of tet(X) in environmental Gram-negative bacteria. A carbapenem- and tigecycline-resistant Shewanella xiamenensis isolate (NUITM-VS1) was obtained from an urban drainage in Hanoi, Vietnam, in March 2021. Whole-genome sequencing analysis was performed by long- and short-read sequencing, resulting in a complete genome sequence. Antimicrobial resistance genes (ARGs) in the genome were detected based on the custom ARG database, including all known tigecycline resistance genes. Shewanella xiamenensis isolate NUITM-VS1 harboured the tet(X4) gene and the bla_OXA-48 carbapenemase gene on the chromosome. tet(X4) was flanked by IS91 family transposase genes, suggesting that the acquisition of tet(X4) was mediated by this mobile gene element (MGE), whereas no MGE was found surrounding bla_OXA-48, consistent with previous findings that bla_OXA-48-like β-lactamase genes are species-specific intrinsic ARGs in Shewanella spp. To the best of our knowledge, this is the first report of a tet(X4)-harbouring Shewanella sp. isolate. Our results provide genetic evidence of the complexity of the dynamics of clinically important ARGs among bacteria in the water environment.

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.