The emergence of metronidazole-resistant Prevotella bivia harboring nimK gene in Japan

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ABSTRACT We present the identification and characterization of the complete genome of metronidazole (MTZ)-resistant Prevotella bivia strain TOH-2715 [minimum inhibitory concentration (MIC): 8 mg/L], isolated from the urine of an elderly Japanese woman, as well as details of its mobile genetic elements (MGEs) containing antimicrobial resistance (AMR) genes and its relationship with other bacterial species determined using whole-genome sequencing (WGS) data. TOH-2715 possessed two chromosomes with putative MGEs containing AMR genes. Two AMR-related MGE regions were present in chromosome 2. MGE-region 1 (7,821 bp) included Tn 6456 , where nimK was located, and MGE-region 2 (58.8 Kbp) included the integrative and conjugative element (ICE), where tet (Q) and ermF were located. The genetic structure of the ICE of TOH-2715 was similar to that of CTn DOT -family transposons, where ermF and tet (Q) are located. A search of public databases revealed that nimK was present in Prevotella spp., including P. bivia , and was partially composed of a Tn 6456 -like element lacking the efflux transporter gene qacE and the Crp/Fnr family transcriptional regulator gene in some cases. Core ICE gene analysis showed that ICEs similar to that of TOH-2715 were present in Prevotella spp. and Bacteroides spp., suggesting horizontal gene transfer among anaerobes. This is the report of WGS analysis of an MTZ-resistant clinical strain of P. bivia (TOH-2715) with Tn 6456 encoding nimK . Other submitted genomes have described the presence of nimK , but none of them have described MTZ resistance. Additionally, we described putative MGE regions containing the AMR gene within the genus Prevotella and among anaerobes, raising concerns about the future spread of nimK among anaerobes. IMPORTANCE Metronidazole (MTZ) is an important antimicrobial agent in anaerobic infections and is widely used in clinical settings. The rate of MTZ resistance in anaerobic bacteria has been increasing in recent years, and the nim gene (nitro-imidazole reductase) is one of the resistance mechanisms. Prevotella bivia is found in humans in the urinary tract and vagina and is known to cause infections in some cases. One of the nim genes, nimK , has recently been discovered in this species of bacteria, but there are no reports of antimicrobial resistance (AMR)-related regions in its whole genome level. In this study, we analyzed the AMR region of nimK -positive P. bivia derived from clinical specimens based on comparisons with other anaerobic genomes. P. bivia was found to be engaged in horizontal gene transfer with other anaerobic bacteria, and the future spread of the nimK gene is a concern.

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