Carbapenem-resistant Salmonella has recently aroused increasing attention. In this study, a total of four sequence type 36 Salmonella enterica subsp. enterica serovar Typhimurium (S. Typhimurium) isolates were consecutively isolated from an 11-month-old female patient with a gastrointestinal infection, of which one was sensitive to carbapenems and three were resistant to carbapenems. Via antibiotic susceptibility testing, a carbapenemases screening test, plasmid conjugation experiments, Illumina short-reads, and PacBio HiFi sequencing, we found that all four S. Typhimurium isolates contained a bla_CTX-M-14-positive IncI1 plasmid. One carbapenem-sensitive S. Typhimurium isolate then obtained an IncHI2 plasmid carrying bla_NDM-1 and an IncP plasmid without any resistance genes during the disease progression. The bla_NDM-1 gene was located on a new 30 kb multiple drug resistance region, which is flanked by IS26 and TnAs2, respectively. In addition, the ST_F0903R isolate contained eight tandem copies of the ISCR1 unit (ISCR1-dsbD-trpF-ble-bla_NDM-1-ISAba125Δ1), but an increase in MICs to carbapenems was not observed. Our work further provided evidence of the rapid spread and amplification of bla_NDM-1 through plasmid. Prompting the recognition of carbapenem-resistant Enterobacterales and the initiation of appropriate infection control measures are essential to avoid the spread of these organisms.

Background: Carbapenem resistant Enterobacteriaceae (CRE) colonization is a risk factor for CRE infection. CRE infection results in an increase in mortality in patients with cirrhosis. However, minimal data regarding the prevalence and the risk factors of CRE colonization in patients with liver disease yet without liver transplantation are available. The present study aimed to investigate the prevalence, risk factors and molecular epidemiology characteristics of CRE fecal carriage among patients with liver disease. Methods: Stool specimens from 574 adult inpatients with liver disease were collected from December 2020 to April 2021. CRE were screened using selective chromogenic agar medium and identified by the Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS). Antimicrobial susceptibility was determined using the broth microdilution method. Carbapenemase genes were characterized by polymerase chain reaction (PCR) and DNA sequencing. Multilocus sequence typing (MLST) was performed for Carbapenem Resistant Klebsiella pneumoniae (CR-KPN) isolates and Carbapenem Resistant Escherichia Coli (CR-ECO) isolates. Results: The total number of stool specimens (732) were collected from 574 patients with liver disease. 43 non-duplicated CRE strains were isolated from 39 patients with a carriage rate of 6.79% (39/574). The carriage rate was 15.60% (17/109) in patients with acute-on-chronic liver failure (ACLF). Multivariate analysis indicated that ACLF (P = 0.018), the history of pulmonary infection within past 3 months (P = 0.001) and the use of third generation cephalosporin/β-lactamases inhibitor within past 3 months (P = 0.000) were independent risk factors of CRE colonization in patients with liver disease. Klebsiella Pnuemoniae (KPN) (51.28%) and Escherichia coli (ECO) (30.77%) were main strains in these patients. All CRE strains showed high resistance to most antimicrobials except for polymyxin B and tigecycline. Most (83.72%, 36/43) of the CRE carried carbapenemase genes. bla_KPC-2 was the major carbapenemase gene. The molecular epidemiology of KPN were dominated by ST11, while the STs of ECO were scattered. Conclusions: The present study revealed that CRE fecal carriage rates were higher in patients with ACLF than in patients without liver failure. ACLF, the history of pulmonary infection within past 3 months and the use of third generation cephalosporin/β-lactamases inhibitor within past 3 months were independent risk factors of CRE colonization in patients with liver disease. Regular CRE screening for hospitalized patients with liver disease should be conducted to limit the spread of CRE strain.

Salmonella enterica subsp. enterica serovar Mbandaka ( S . Mbandaka) represents an emerging public health threat due to its remarkable genomic adaptability, involvement in multinational foodborne outbreaks, and the ability to establish persistent infections. Here, we report the first documented isolation of a carbapenem-resistant S . Mbandaka strain, a significant public health concern given the critical role of carbapenems in treating multidrug-resistant infections. Five clonal S . Mbandaka isolates were obtained from a single patient, with three isolates (SM_F22R, SM_F28R, and SM_B30R) exhibiting carbapenem resistance mediated by the bla _NDM-1 . The comprehensive genomic analysis uncovered a 1,220 kb chromosomal inversion mediated by IS 26 through intramolecular replicative transposition (in trans ), generating the SM_F28R and SM_B30R variants. Using S1 pulsed-field gel electrophoresis, Southern blotting, and conjugation experiments, we demonstrated the transfer of bla _NDM-1 : chromosomal localization in SM_F22R and plasmid-borne (IncC-type) carriage in SM_F28R and SM_B30R. Notably, the region carrying bla _NDM-1 in both locations was flanked by IS 26 and completely identical, indicating that IS 26 may facilitate the transfer of bla _NDM-1 between the chromosome and plasmid. Additionally, we detected the amplification of mph(A ) on the chromosome and bla _NDM-1 on the IncC plasmid. The expression level of bla _NDM-1 in SM_F22R was lower than that in SM_F28R and SM_B30R, consistent with SM_F22R exhibiting lower carbapenem resistance compared to SM_F28R and SM_B30R. This study reported the IS 26 -mediated transfer of bla _NDM-1 between the chromosome and a plasmid in S . Mbandaka, highlighting the critical role of transposable elements in disseminating carbapenem resistance. IMPORTANCE: As a clinically significant foodborne pathogen, carbapenem-resistant Salmonella presents a significant therapeutic challenge due to its extensive antibiotic resistance. While bla _NDM-1 is conventionally plasmid-borne, our study elucidates its transfer between chromosomes and a conjugative IncC plasmid in Salmonella . Our findings demonstrate the pivotal involvement of IS 26 and IS CR1 mobile genetic elements in orchestrating genomic rearrangements while concurrently mediating the horizontal transfer and subsequent amplification of antimicrobial resistance determinants. This study provides an important theoretical basis for an in-depth analysis of the horizontal transfer mechanism of bacterial resistance genes.

Objectives: This study aimed to identify differences in risk factors for carbapenem-resistant Enterobacteriaceae (CRE) infections across different anatomical sites and to explore risk factors associated with mortality in CRE-infected patients. Methods: Patients who underwent CRE screening and were subsequently diagnosed with CRE infections were included and categorized by infection site: respiratory tract (RTI), urinary tract (UTI), and bloodstream (BSI). Forty ICU patients without CRE infection were randomly selected as controls. Statistical comparisons were performed using the Mann–Whitney U or Chi-square test, as appropriate. Potential risk factors were evaluated via univariate and multivariate analyses, and a predictive model was constructed, with its performance assessed using ROC curve analysis. Results: CRE colonization was identified as a common independent risk factor across all three groups (RTI, UTI, and BSI). Infection-site-specific analyses revealed independent risk factors: RTI was associated with mechanical ventilation, UTI with trauma, and BSI with gastrointestinal injury. Predictive models for RTI, UTI, and BSI demonstrated good discrimination, with ROC AUCs of 0.94, 0.94, and 0.95, respectively. In the analysis of Survived versus Deceased patients, the BSI group had the highest mortality, though the difference was not statistically significant. Deceased patients exhibited significantly higher PCT levels than Survived patients (p = 0.005). Prior use of carbapenems and antifungal agents, as well as Ln(PCT), were independently associated with mortality in CRE-infected patients. Conclusions: Risk factors for CRE infections vary across anatomical sites, with CRE colonization, mechanical ventilation, trauma, and gastrointestinal injury playing key roles. Overuse of antibiotics and elevated inflammatory responses are associated with increased mortality. These findings provide evidence for early identification of high-risk patients and optimization of individualized treatment strategies.