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Purpose: The isolation rate of carbapenem-resistant Enterobacter cloacae complex (CREC) is continuously increasing. The aims of this study were to investigate the molecular characteristics and risk factors associated with CREC infections. Methods: Bacterial species were identified using the matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) (Bruker Daltonik GmbH, Bremen, Germany), and the hsp60 gene was utilized for further typing. Antimicrobial susceptibilities were assessed through the MicroScan WalkAway 96 Plus system (Siemens, Germany) and the microbroth dilution method. Antimicrobial resistance genes were screened through polymerase chain reaction (PCR), while the homologous relationship was assessed using multilocus sequence typing (MLST). Conjugation experiments were performed to verify whether the plasmid could be transferred. Additionally, logistic regression model was employed to analyze risk factors for CREC infections. Results: 32 strains of CREC bacteria were isolated during the study, yet only 20 were retained for preservation. While the isolates demonstrated resistance to the majority of antibiotics, they exhibited high sensitivity to polymyxin B and tigecycline. All isolates carried the blaNDM resistance gene, including 13 blaNDM-1 isolates and 7 blaNDM-5 isolates. MLST homology analysis revealed the presence of seven known ST types and one new ST type. Conjugation experiments confirmed that 13 isolates were capable of transferring the blaNDM resistance gene to Escherichia coli strain EC600. Single-factor analysis identified multiple primary risk factors for CREC infection, but multivariate analysis did not reveal independent risk factors. Conclusion: This study investigates the molecular characteristics and risk factors associated with CREC infections. The detection rate of CREC strains in our hospital is continuously rising and homology analysis suggested that strains might spread in our hospital, emphasizing the importance of implementing effective preventive measures to control the horizontal transmission of plasmid-mediated antimicrobial resistance genes.
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Carbapenem-resistant Acinetobacter baumannii (CRAB) has become one of the leading causes of healthcare-associated infections globally, particularly in intensive care units (ICUs). Cross-transmission of microorganisms between patients and the hospital environment may play a crucial role in ICU-acquired CRAB colonization and infection. The control and treatment of CRAB infection in ICUs have been recognized as a global challenge because of its multiple-drug resistance. The main concern is that CRAB infections can be disastrous for ICU patients if currently existing limited therapeutic alternatives fail in the future. Therefore, the colonization, infection, transmission, and resistance mechanisms of CRAB in ICUs need to be systematically studied. To provide a basis for prevention and control countermeasures for CRAB infection in ICUs, we present an overview of research on CRAB in ICUs, summarize clinical infections and environmental reservoirs, discuss the drug resistance mechanism and homology of CRAB in ICUs, and evaluate contemporary treatment and control strategies.
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Emergence of bla NDM-1 and bla KPC-2 co-producing Klebsiella pneumoniae strains is currently attracting widespread attention, but little information is available about their tigecycline resistance, virulence, and prevalence in Southwest China. In July 2021, an extensively drug-resistant K. pneumoniae strain AHSWKP25 whose genome contained both bla NDM-1 and bla KPC-2 genes was isolated from the blood of a patient with the malignant hematological disease in Luzhou, China. We investigated the resistance profiles of AHSWKP25 using microbroth dilution, agar dilution, modified carbapenemase inactivation (mCIM), and EDTA-modified carbapenemase inactivation methods (eCIM). The virulence of AHSWKP25 was assessed through string tests, serum killing assays, and a Galleria mellonella larval infection model. Conjugation and plasmid stability experiments were conducted to determine the horizontal transfer capacity of plasmids. And efflux pump phenotype test and real-time quantitative reverse transcription-PCR (RT-PCR) were used to determine its efflux pump activity. Sequencing of AHSWKP25 determined that AHSWKP25 belonged to ST464, which is resistant to antibiotics such as carbapenems, tetracycline, fluoroquinolones, tigecycline, and fosfomycin. The efflux pump phenotype tests and RT-PCR results demonstrated that efflux pumps were overexpressed in the AHSWKP25, which promoted the tigecycline resistance of the bacteria. AHSWKP25 also showed hypervirulence and serum resistance in vitro model. AHSWKP25 carried several different plasmids that contained bla NDM-1, bla KPC-2, and mutated tet(A) genes. Sequence alignment revealed that the plasmids carrying bla NDM-1 and bla KPC-2 underwent recombination and insertion events, respectively. We demonstrated that an X3 plasmid carrying bla NDM-1 was transferred from pSW25NDM1 to E. coli J53. We also identified missense mutations in the ramR, rcsA, lon, and csrD genes of AHSWKP25. Our results highlighted the potential of bla NDM-1 and bla KPC-2 co-producing K. pneumoniae strains to further develop antimicrobial resistance and hypervirulent phenotypes, but measures should be taken to closely monitor and control the spread of superbugs with multidrug-resistant phenotypes and hypervirulence.
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Background: Colistin is one of the few options for treating carbapenem-resistant Enterobacterales (CREs). There is little available information about the epidemic status of colistin-resistant CREs in Southern Sichuan, China. This study mainly investigated the genomic and phenotypic characteristics of an extensively drug resistant E. coli LZ00114 isolated from Luzhou, China. Materials and Methods: In 2020, LZ00114 was isolated from the urine of a patient with hydronephrosis and urinary tract infection in Luzhou, China. We assessed the resistance profile of LZ00114 in the presence and absence of the protonophore carbonyl cyano-m-chlorophenylhydrazine (CCCP) and 1-(1-naphthylmethyl)-piperazine (NMP) by antimicrobial susceptibility testing. The growth kinetics, motility, and pathogenicity of LZ00114 were determined to evaluate its microbial characteristics. In combination with whole genome sequencing (WGS) and real-time reverse transcription PCR (RT-PCR), we comprehensively analyzed the resistance mechanisms of LZ00114. Results: LZ00114 was resistant to various antimicrobial agents, including meropenem, tetracycline, ciprofloxacin, gentamicin, fosfomycin, and polymyxin B. Notably, CCCP reversed the resistance of LZ00114 to polymyxin B. LZ00114 displayed high pathogenicity in the infection model (P<0.01) compared with the Lab-WT strain, and its growth rate and motility were not significantly different from the Lab-WT strain. WGS and conjugation revealed that LZ00114 belonged to ST410 and carried a bla NDM-5-harboring self-transmissible IncX3 plasmid and a multi-replicon IncFII/FIA/FIB plasmid carrying bla OXA-1-bla CTX-M-55-tet(B)-aac(6')-Ib-cr-dfrA17-sul1-fosA3. Comparative genomics revealed genetic relatedness between LZ00114 and strains isolated from other regions. Furthermore, there were point mutations in pmrA (S29G, G144S), pmrB (D283G, Y358N), marR (G103S, Y137H), emrA (I219V), and emrD (G323D) of LZ00114. RT-PCR confirmed the overexpression of efflux pumps and PmrABC in LZ00114. Conclusion: This study provides valuable information for the surveillance of antimicrobial resistance and a theoretical basis for the prevention and control of colistin-resistant E. coli. There is still a need to be vigilant about the clone spread of the high-risk clone group E. coli ST410.