Complete genome sequence of cfr(B)-carrying Enterococcus raffinosus isolated from bile in a patient in Japan.

OBJECTIVES: Linezolid is an antibiotic used to treat infectious diseases caused by vancomycin-resistant enterococci and methicillin-resistant Staphylococcus aureus. Recently, Enterococcus Spp.-carrying mobile linezolid resistance genes were reported. Herein, we report the complete genome sequence of Enterococcus raffinosus JARB-HU0741, which was isolated from a bile sample of a patient in Japan on May 5, 2021, and carries a linezolid resistance gene, cfr(B). Nevertheless, this isolate was susceptible to linezolid. METHODS: Whole-genome sequencing was performed using HiSeq X FIVE (Illumina) and GridION (Oxford Nanopore Technologies). The sequence reads were assembled using Unicycler v0.4.8, and the complete genome was annotated using DFAST v1.2.18. Antimicrobial resistance genes were detected with Abricate v1.0.1, using the ResFinder database. The minimum inhibitory concentrations (MICs) were determined using broth microdilution and interpreted according to the guidelines of the Clinical and Laboratory Standards Institute. RESULTS: E. raffinosus JARB-HU0741 contained a 3 248 808-bp chromosome and a 1 156 277-bp megaplasmid. cfr(B) was present in the Tn6218-like transposon, which was inserted into a gene encoding a PRD domain-containing protein present in the megaplasmid, but the isolate was susceptible to linezolid (MIC, 0.5 µg/mL). The Tn6218-like transposon was similar to the Tn6218 of Clostridioides difficile Ox3196 and the Tn6218-like transposon of Enterococcus faecium UW11733; however, three genes encoding a topoisomerase, an S-adenosylmethionine-dependent methyltransferase, and a TetR family transcriptional regulator were present in the previous Tn6218- or Tn6218-like transposon. CONCLUSION: This is the first report of the complete genome sequence of E. raffinosus carrying cfr(B). E. raffinosus carrying cfr(B) without linezolid resistance poses a threat, as it could serve as a reservoir for mobile linezolid resistance genes.

Complete genome sequence of optrA-carrying Enterococcus faecalis isolated from open pus in a Japanese patient.

OBJECTIVES: The occurrence of linezolid resistance in enterococci has recently increased. Here, we report the genomic characterization of Enterococcus faecalis strain JARB-HU0796-isolated from the open pus of a patient in Hiroshima, Japan-which shows nonsusceptibility to linezolid (MIC of 4 µg/mL). METHODS: JARB-HU0796 whole-genome sequencing was performed using short-read sequencing with Illumina Hiseq X Five and long-read sequencing using GridION. These reads were collected using the assembly pipeline Unicycler and annotated with DFAST. Antimicrobial resistance genes were detected using the Abricate and ResFinder databases, and the sequence type identified using PubMLST. The antimicrobial susceptibility of JARB-HU0796 was determined with the Eiken dry-plate QH02 system. RESULTS: The JARB-HU0796 complete genome contained a circular chromosome (2 722 585 bp) and two circular plasmids (85 996 bp and 58 872 bp). The chromosome harbours the optrA gene, which confers resistance to oxazolidinones and phenicols. JARB-HU0796 showed nonsusceptibility to linezolid and multidrug resistance to other antibiotics. MLST analysis identified JARB-HU0796 as ST476, similar to the optrA-positive E. faecalis ST476 isolates from swine (South Korea, 2020) and pet food (Switzerland, 2022). The optrA region of JARB-HU0796 is nearly identical to that of ST476 E. faecalis strain TZ2, isolated from humans (China, 2013). CONCLUSIONS: To the best of our knowledge, this is the first report of the complete genome sequence of E. faecalis ST476 carrying optrA on a chromosome isolated from a patient in Japan. The strain may have originated in animals, suggesting that the organisms acquired resistance to linezolid because the optrA gene may be closely spread between animals and humans.

Prevalence of Mycoplasma hominis, Ureaplasma urealyticum, and Ureaplasma parvum detection in urine and respiratory tract samples in Hiroshima, Japan.

Background: Mycoplasma hominis, Ureaplasma parvum, and Ureaplasma urealyticum are commensal bacteria that are associated with colonization and infection of the urogenital tract. However, colonization of the respiratory tract by these microorganisms in adults has not been fully investigated. Methods: Urine and respiratory tract samples (sputum, tracheal aspirates, and bronchoalveolar lavage) of patients aged 20-80 years were analyzed to detect the presence of M. hominis, U. parvum, and U. urealyticum using a conventional PCR method. The samples were submitted to the microbiological clinical laboratory of Hiroshima University Hospital from December 1, 2021 to May 31, 2022. Results: In total, 334 urine and 238 respiratory tract samples were analyzed. The overall detection rates of M. hominis, U. parvum, and U. urealyticum were 2.9%, 1.7%, and 2.3% in male urine; 7.0%, 13.8%, and 1.9% in female urine; 2.2%, 0%, and 2.2% in male respiratory tract; and 0%, 2.0%, and 0% in female respiratory tract, respectively. In urine samples, the detection rates of M. hominis, U. parvum, and U. urealyticum were significantly higher (p < 0.001) for women (29/159; 18.2%) than for men (10/175; 5.7%); however, in respiratory tract samples, the detection rates were not significantly different (p = 0.70) between women (2/101; 2.0%) and men (5/137; 3.7%). Further, both the urine and respiratory samples of 83 patients were analyzed. Three male samples were positive for M. hominis or U. urealyticum, and M. hominis and U. urealyticum were matched in both the urine and respiratory tract samples: M. hominis (n = 1), U. urealyticum (n = 1), M. hominis + U. urealyticum (n = 1). Conclusion: M. hominis, U. parvum, and U. urealyticum were detected in the respiratory tract of not only the young patients, but also of patients aged 50-60 years. Further studies are required to understand the relationship of these microorganisms in urogenital and respiratory tract samples with extra-genital infections.

Different CprABC amino acid sequences affect nisin A susceptibility in Clostridioides difficile isolates.

Clinical isolates of Clostridioides difficile sometimes exhibit multidrug resistance and cause diarrhea after antibiotic administration. Metronidazole and vancomycin are often used as therapeutic agents, but resistance to these antibiotics has been found clinically. Therefore, the development of alternative antimicrobial agents is needed. Nisin A, produced by Lactococcus lactis, has been demonstrated to be effective against C. difficile infection. In this study, we evaluated the susceptibility of 11 C. difficile clinical isolates to nisin A and found that they could be divided into 2 groups: high and low susceptibility. Since CprABC and DltDABC, which are responsible for nisin A efflux and cell surface charge, respectively, have been reported to be related to nisin A susceptibility, we investigated the expression of cprA and dltA among the 11 strains. cprA expression in all strains was induced by nisin A, but dltA expression was not. The expression levels of both genes did not correlate with nisin A susceptibility in these clinical isolates. To evaluate cell surface charge, we performed a cytochrome C binding assay and found no relationship between charge and nisin A susceptibility. Then, we determined the whole genome sequence of each clinical isolate and carried out phylogenetic analysis. The 11 isolates separated into two major clusters, which were consistent with the differences in nisin A susceptibility. Furthermore, we found common differences in several amino acids in the sequences of CprA, CprB, and CprC between the two clusters. Therefore, we speculated that the different amino acid sequences of CprABC might be related to nisin A susceptibility. In addition, C. difficile strains could be divided in the same two groups based on susceptibility to epidermin and mutacin III, which are structurally similar to nisin A. These results suggest that genotypic variations in C. difficile strains confer different susceptibilities to bacteriocins.

Seroepidemiological study of factors affecting anti-spike IgG antibody titers after a two-dose mRNA COVID-19 vaccination in 3744 healthy Japanese volunteers.

Several factors related to anti-spike(S) IgG antibody titers after mRNA COVID-19 vaccination have been elucidated, but the magnitude of the effects of each factor has not been fully understood. This cross-sectional study assessed anti-S and anti-nucleocapsid (N) antibody titers on 3744 healthy volunteers (median age, 36 years; IQR, 24-49 years; females, 59.0%) who received two doses of mRNA-1273 or BNT162b2 vaccine and completed a survey questionnaire. Multiple regression was conducted to identify factors associated with antibody titers. All but one participant tested positive for anti-S antibodies (99.97%). The following factors were independently and significantly associated with high antibody titer: < 3 months from vaccination (ratio of means 4.41); mRNA-1273 vaccine (1.90, vs BNT162b2); anti-N antibody positivity (1.62); age (10's: 1.50, 20's: 1.37, 30's: 1.26, 40's: 1.16, 50's: 1.15, vs ≧60's); female (1.07); immunosuppressive therapy (0.54); current smoking (0.85); and current drinking (0.96). The largest impact on anti-S IgG antibody titers was found in elapsed time after vaccination, followed by vaccine brand, immunosuppressants, previous SARS-CoV-2 infection (anti-N antibody positive), and age. Although the influence of adverse reactions after the vaccine, gender, smoking, and drinking was relatively small, they were independently related factors.

The tumor-infiltrating lymphocyte ultrasonography score can provide a diagnostic prediction of lymphocyte-predominant breast cancer preoperatively.

PURPOSE: Tumor-infiltrating lymphocytes (TILs) are known to predict the therapeutic effect in breast cancer. Although a preoperative tissue biopsy can be used to evaluate TILs, TILs that are heterogeneously distributed might require examination of all preoperative tissue biopsy samples. We have recently reported that the TIL ultrasonography (US) score, as determined by characteristic US findings, provides excellent predictive performance for lymphocyte predominant breast cancer (LPBC). We herein aimed to determine whether the preoperative TIL-US score can more accurately predict LPBC than preoperative tissue biopsy. METHODS: We assessed 161 patients with invasive breast cancer that were treated with curative surgery between January 2014 and December 2017. Stromal lymphocytes were examined on preoperative tissue biopsy tissues and surgical pathological specimens. Breast cancer samples with ≥ 50% stromal TILs were defined as pre-LPBC (preoperative tissue biopsy) and LPBC (surgical pathological specimens). Useful factors for predicting LPBC were searched among clinicopathological factors. RESULTS: The TIL-US score cutoff value for predicting LPBC was 4 points based on the receiver operating characteristic curves (area under the curve: 0.88). Several significant predictors for LPBC were revealed by the undertaken multivariate logistic regression analysis (odds ratios: TIL-US score, 26.8; pre-LPBC, 18.6; HER2, 9.2; all, p < 0.05). The sensitivity, specificity, accuracy, positive predictive value, and negative predictive value were 0.74, 0.89, 0.85, 0.67, and 0.92 for the TIL-US score, respectively, and 0.51, 0.98, 0.87, 0.91, and 0.86 for the pre-LPBC, respectively. CONCLUSION: TIL-US scores can predict LPBC preoperatively and are characterized by a significantly high sensitivity and negative predictive value.

A longitudinal study of anti-SARS-CoV-2 antibody seroprevalence in a random sample of the general population in Hiroshima in 2020.

BACKGROUND: This longitudinal study aimed to determine chronological changes in the seroprevalence of prior SARS-CoV-2 infection, including asymptomatic infections in Hiroshima Prefecture, Japan. METHODS: A stratified random sample of 7,500 residents from five cities of Hiroshima Prefecture was selected to participate in a three-round survey from late 2020 to early 2021, before the introduction of the COVID-19 vaccine. The seroprevalence of anti-SARS-CoV-2 antibodies was calculated if at least two of four commercially available immunoassays were positive. Then, the ratio between seroprevalence and the prevalence of confirmed COVID-19 cases in Hiroshima was calculated and compared to the results from other prefectures where the Ministry of Health, Labour and Welfare conducted a survey by using the same reagents at almost the same period. RESULTS: The numbers of participants in the first, second, and third rounds of the survey were 3025, 2396, and 2351, respectively and their anti-SARS-CoV-2 antibodies seroprevalences were 0.03% (95% confidence interval: 0.00-0.10%), 0.08% (0.00-0.20%), and 0.30% (0.08-0.52%), respectively. The ratio between the seroprevalence and the prevalence of confirmed COVID-19 cases in Hiroshima was 1.2, which was smaller than that in similar studies in other prefectures. CONCLUSIONS: The seroprevalence of anti-SARS-CoV-2 antibodies in Hiroshima increased tenfold in a half year. The difference between seroprevalence and the prevalence of confirmed COVID-19 cases in Hiroshima was smaller than that in other prefectures, suggesting that asymptomatic patients were more actively detected in Hiroshima.

Clinical characteristics of Actinotignum schaalii bacteremia in a Japanese tertiary hospital.

We retrospectively analyzed seven patients with Actinotignum schaalii bacteremia in a tertiary hospital in Japan. Pyelonephritis was the most frequent source of bacteremia, followed by Fournier's gangrene and pyometra. All patients with pyelonephritis had underlying urological conditions, ureteral stents, nephrostomy, ureteral stones, or ureterocele.

Clinical and microbiological characteristics of Eggerthella lenta bacteremia at a Japanese tertiary hospital.

Eggerthella lenta is an important cause of anaerobic bloodstream infections and is associated with high mortality. However, there are few reports of E. lenta infection in Japan. This study aimed to evaluate the clinical and microbiological characteristics of bacteremia caused by E. lenta in Hiroshima, Japan. We retrospectively analyzed E. lenta bacteremia patients at the Hiroshima University Hospital between January 2012 and December 2020. During the study period, 14 patients with E. lenta bacteremia were identified. All E. lenta isolates were cultured in anaerobic bottles, and the median time to blood culture positivity was 52.9 h. In most cases (85.6%), the source of E. lenta bacteremia was associated with intra-abdominal infections, and colon perforation was the most frequent source of E. lenta bacteremia (42.9%, n = 6). Antimicrobial susceptibility testing showed high minimal inhibitory concentrations (MIC) of piperacillin-tazobactam (TZP) and 100% susceptibility to ampicillin-sulbactam, carbapenems, and metronidazole. This study demonstrates that E. lenta bacteremia is associated with intra-abdominal infections, particularly colon perforation, and a high MIC of TZP. When gram-positive anaerobes are detected in the blood cultures of patients with severe intra-abdominal infections, clinicians should suspect E. lenta, and it may be better to change antimicrobial agents from TZP.

Ultrasonography Combined With Contrast-enhanced Ultrasonography Can Predict Lymphocyte-predominant Breast Cancer.

Background: We investigated whether contrast-enhanced ultrasonography (CEUS) scores can predict lymphocyte-predominant breast cancer (LPBC). Patients and Methods: We evaluated 75 patients who underwent US and CEUS. LPBC was defined as tissues with ≥50% stromal tumour-infiltrating lymphocytes (TILs) preoperatively. Characteristic US images predicting LPBC were evaluated using TIL-US scores via three ultrasonic tissue characteristics: Shape, internal echo level, and posterior echoes. TIL-CEUS was evaluated based on TIL-US plus CEUS. Results: TIL-US and TIL-CEUS cut-offs for predicting LPBC were 4 and 6 (area under the curve=0.93 and 0.96, respectively) points based on receiver operating characteristics curves. Sensitivity, specificity, and accuracy values (95% confidence intervaI) were 0.94 (0.77-0.99), 0.75 (0.70-0.77), and 0.80 (0.72-0.82); and 0.94 (0.78-0.99), 0.86 (0.81-0.87), and 0.88 (0.80-0.90) for TIL-US and TIL-CEUS, respectively. TIL-CEUS score was a significant single predictor for LPBC in multivariate logistic regression (p=0.001). Conclusion: TIL-CEUS can be used for preoperative LPBC prediction and detection.

Concomitant emphysema might increase the false-negative rate of urinary antigen tests in patients with pneumococcal pneumonia: results from a retrospective study.

The urinary antigen test (UAT) is a rapid diagnostic method for pneumococcal pneumonia, but the high false-negative rate of 30% may affect its reliability. To maximize the utility of UAT, it is necessary to investigate the patient factors affecting UAT results. However, there is no report elucidating the association between its utility and pre-existing lung abnormalities. We retrospectively reviewed 388 patients with pneumococcal pneumonia confirmed by blood and/or sputum culture tests. Finally, 94 of 388 patients who had the results of UAT and computed tomography scans were enrolled to evaluate the association between the utility of UAT and patient factors including pulmonary emphysema and fibrosis. The overall positive rate of UAT was 69.1%. The positive rates of UAT in the patients with emphysema were significantly lower than those in individuals without emphysema (33.3% and 77.6%, p < 0.001). Univariate logistic regression analysis showed that the presence of emphysema was associated with a low positive rate (odds ratio 6.944, 95% confidence interval 2.268-21.231). Multivariate logistic analysis showed that the presence of emphysema and lower levels of serum blood urea nitrogen (BUN) were significantly and independently associated with a low positive rate. The combination of emphysema and BUN can potentially stratify the positive rate of UAT in patients with pneumococcal pneumonia. Patients with pneumococcal pneumonia and emphysema have a lower positive rate of UAT. Additionally, the combination of emphysema and serum BUN value may be useful to evaluate the reliability of the negative results of pneumococcal UAT.

Liver fibrosis assessments using FibroScan, virtual-touch tissue quantification, the FIB-4 index, and mac-2 binding protein glycosylation isomer levels compared with pathological findings of liver resection specimens in patients with hepatitis C infection.

BACKGROUND: Evaluation of fibrosis stage is important to monitor progression of liver disease and risk of hepatocellular carcinoma (HCC). While liver biopsy is the gold standard, the method is invasive and faces several limitations. The aim of this study was to determine correlations among METAVIR scores and FibroScan, Virtual-Touch tissue quantification (VTQ), fibrosis index based on four factors (FIB-4 index), and Mac-2 binding protein glycosylation isomer (M2BPGi) level, and for examine differences in the reliability of non-invasive methods to evaluate fibrosis. METHODS: We used liver resection specimens from patients with hepatitis C virus (HCV), correlations were assessed between METAVIR scores and non-invasive method. Receiver operating characteristic (ROC) curves were generated to determine the sensitivity, specificity, and cut off values of the methods. RESULTS: All Patients group: In F0-2 vs F3-4, the areas under the ROC curve (AUC) (0.85) of FibroScan was significantly higher than that (0.67) of FIB-4 index (p = 0.002) and that (0.67) of M2BPGi (p = 0.001). The AUC (0.83) of VTQ was significantly higher than that (0.67) of FIB-4 index (p = 0.01) and that (0.67) of M2BPGi (p = 0.002). In F0-3 vs F4, the AUC (0.86) of VTQ was significantly higher than that (0.65) of FIB-4 index (p = 0.04). The AUC (0.89) of FibroScan was significantly higher than that (0.65) of FIB-4 index (p = 0.002) and that (0.76) of M2BPGi (p = 0.02). Non-SVR group: In F0-2 vs F3-4, the AUC (0.85) of FibroScan was significantly higher than that (0.84) of FIB-4 index (p = 0.02) and that (0.73) of M2BPGi (p = 0.003). The AUC (0.84) of VTQ was significantly higher than that (0.74) of FIB-4 index (p = 0.04). In F0-3 vs F4, the AUC (0.91) of FibroScan was significantly higher than that (0.67) of FIB-4 index (p = 0.003) and that (0.78) of M2BPGi (p = 0.02). The AUC (0.88) of VTQ was significantly higher than that of FIB-4 index (0.67) and that of M2BPGi (0.78) (p = 0.04). CONCLUSIONS: FibroScan and VTQ best reflected the results of hepatic fibrosis diagnosis using liver resection specimens among the four examination methods evaluated.

Novel tumor-infiltrating lymphocytes ultrasonography score based on ultrasonic tissue findings predicts tumor-infiltrating lymphocytes in breast cancer.

BACKGROUND: The presence of tumor-infiltrating lymphocytes (TILs) is a prognostic factor for breast cancer. However, because of tumor tissue heterogeneity, an accurate and simple evaluation method is needed. We determined if preoperative characteristic ultrasonography (US) image findings are predictive of lymphocyte-predominant breast cancer (LPBC). METHODS: We evaluated 191 patients with invasive breast cancer treated by curative surgery between January 2014 and December 2017. Stromal lymphocytes in surgical pathological specimens were evaluated. Fifty-two patients with ≥ 50% stromal TILs were defined as having LPBC. Preoperative US images were examined for indicators of TILs. The US images with characteristic TILs were scored for prediction of LPBC. RESULTS: Shape (more lobulated), internal echo level (weaker), and posterior echoes (stronger) were predictors of LPBC and used to assign the TILs-US scores (0-7 points); the score cutoff for predicting LPBC was 4 points (sensitivity, 0.73; specificity, 0.87; accuracy, 0.83) based on the receiver operating characteristics (ROC) curves (AUC 0.88). Multivariate logistic regression analysis identified nuclear grade (NG), OR 3.4; estrogen receptor (ER), OR 5.7; human epidermal growth factor receptor type-2 (HER2), OR 4.1; and TILs-US score, OR 14.9 as LPBC predictors (all, p < 0.05). The sensitivity, specificity, and accuracy for predicting LPBC were 0.75, 0.69, and 0.71 for NG and 0.33, 0.96, and 0.79 for ER and HER2, respectively. ROC analysis showed that the diagnostic abilities of NG, ER, and HER2 were lower than that of the TILs-US score. CONCLUSIONS: LPBC showed characteristic US imaging findings. The TILs-US score was an accurate preoperative predictor of LPBC.

Clinical features and predictive value of serum inflammatory markers of perivascular involvement in immunoglobulin G4-related disease.

Vascular and/or perivascular involvements of sclerotic inflammation (perivasculitis) are a complication of immunoglobulin G4-related disease (IgG4-RD). We sought to examine clinical manifestations of perivasculitis by computed tomography (CT) in patients with elevated serum IgG4 levels, and then to evaluate some potential predictors of perivasculitis in definite IgG4-RD patients. From a database of patients with serum IgG4 measurements, we selected 81 patients with elevated serum IgG4 levels (≥135 mg/dl). Perivasculitis was defined radiologically as thickened contrast-enhanced rind surrounding the aorta and its major artery on CT imaging. We found 15 patients with perivasculitis; 10 patients in the definite (n = 37), four in the possible (n = 18), and one in the excluded (n = 26) IgG4-RD groups. Clinical predictors of perivasculitis were investigated in 34 untreated patients with definite IgG4-RD. Patients with perivasculitis (n = 10) had significantly higher age at diagnosis (74.2 ± 8.8 vs 63.5 ± 9.9 years, P = 0.006), higher levels of serum IgG4 (754 vs 292 mg/dl, P = 0.007) and C-reactive protein (CRP, 0.52 mg/dl vs 0.10 mg/dl, P = 0.001) than patients without perivasculitis (n = 24). The sensitivity and specificity of serum CRP ≥0.25 mg/dl for identifying perivasculitis in the definite IgG4-RD group were 100 and 71%, respectively (area under the receiver operating characteristic curve 0.863). Our results indicate that IgG4-related perivasculitis was associated with elevated levels of serum CRP and older age, and that CRP may be a useful marker for detecting perivascular involvement in IgG4-RD.

Wisteria floribunda agglutinin positive Mac-2-binding protein level increases in patients with acute liver injury.

BACKGROUND: Wisteria floribunda agglutinin positive human Mac-2-binding protein glycosylation isomer (M2BPGi) is a novel serum glycomarker for liver fibrosis. However, it is not known whether or not M2BPGi reflects only liver fibrosis. We measured serum M2BPGi levels in patients with acute liver injury. METHODS: Fifty-one patients with acute liver injury were enrolled. M2BPGi levels were measured at the initial visit and at achievement of recovery. The relationship between M2BPGi values at the initial visit and clinical outcomes was analyzed. RESULTS: Serum M2BPGi levels at the initial visit were elevated in 47 of 51 acute liver injury patients (8.33 ± 7.56 cutoff index). M2BPGi values were associated with prothrombin activity (r = -0.600, P = 0.001), total bilirubin level (r = 0.588, P = 0.001), and Model for End-Stage Liver Disease score (r = 0.490, P = 0.001) but not with aspartate aminotransferase (r = -0.070) and alanine aminotransferase (r = -0.073) levels. M2BPGi values at the initial visit were significantly higher in patients with acute liver failure (diagnosed by prothrombin activity of 40% or less; P < 0.001), subsequent development of hepatic coma (P = 0.036), and subsequent requirement of liver transplant (P = 0.014), and in a patient who died (P = 0.045). M2BPGi values decreased after aminotransferase level normalization in patients who recovered from acute liver injury; however, M2BPGi level was not a predictive factor for recovery with medical therapy. CONCLUSIONS: Serum M2BPGi values increased in patients with acute liver injury and decreased following recovery. The marker seems to reflect not only liver fibrosis but also other factors, such as liver inflammation, liver damage, and hepatocyte regeneration.

Complete nucleotide sequence of the IncN plasmid encoding IMP-6 and CTX-M-2 from emerging carbapenem-resistant Enterobacteriaceae in Japan.

We have determined the DNA sequence of Klebsiella pneumoniae multidrug resistance plasmid pKPI-6, which is a self-transmissible IncN-type plasmid. pKPI-6 harboring blaIMP-6 and blaCTX-M-2 confers a stealth-type carbapenem resistance phenotype on members of the family Enterobacteriaceae that is not detectable with imipenem. pKPI-6 is already epidemic in Japan, favoring the dissemination of IMP-6 and CTX-M-2 in members of the family Enterobacteriaceae.