UNASSIGNED: This research aims to profile ten novel strains of carbapenem-resistant Enterobacteriaceae (CRE) co-carrying blaKPC and blaNDM.
UNASSIGNED: Clinical CRE strains, along with corresponding medical records, were gathered. To ascertain the susceptibility of the strains to antibiotics, antimicrobial susceptibility tests were conducted. To validate the transferability and cost of fitness of plasmids, conjugation experiments and growth curves were employed. For determining the similarity between different strains, ERIC-PCR was utilised. Meanwhile, whole genome sequencing (WGS) was performed to characterise the features of plasmids and their evolutionary characteristics.
UNASSIGNED: During the course of this research, ten clinical CRE strains co-carrying blaKPC and blaNDM were gathered. It was discovered that five out of these ten strains exhibited resistance to tigecycline. A closer examination of the mechanisms underlying tigecycline resistance revealed that tmexCD1-toprJ1, blaKPC-2, and blaNDM-1 existed concurrently within a single Citrobacter freundii strain (CF10). This strain, with a minimum inhibitory concentration (MIC) of 32 mg/L to tigecycline, was obtained from a sepsis patient. Furthermore, an investigation of genome evolution implied that CF10 belonged to a novel ST type 696, which lacked analogous strains. Aligning plasmids exposed that similar plasmids all had less than 70% coverage when compared to pCF10-tmexCD1, pCF10-KPC, and pCF10-NDM. It was also found that tmexCD1-toprJ1, blaKPC-2, and blaNDM-1 were transferred by Tn5393, IS5, and Tn6296, respectively.
UNASSIGNED: This research presents the first report of coexistence of tmexCD1-toprJ1, blaKPC-2, and blaNDM-1 in a carbapenem and tigecycline-resistant C. freundii strain, CF10.
UNASSIGNED: Tigecycline is considered a \"last resort\" antibiotic for treating CRE infections. The ongoing evolution of resistance mechanisms to both carbapenem and tigecycline presents an alarming situation. Moreover, the repeated reporting of both these resistance mechanisms within a single strain poses a significant risk to public health. The research revealed that the genes tmexCD1-toprJ1, blaKPC-2, and blaNDM-1, which cause carbapenem and tigecycline-resistance in the same strain, were located on mobile elements, suggesting a potential for horizontal transmission to other Gram-negative bacteria. The emergence of such a multi-resistant strain within hospitals should raise significant concern due to the scarcity of effective antimicrobial treatments for these \"superbugs\".

OBJECTIVE: Here, we report a case of severe infection caused by Escherichia coli that harbored mcr-1, bla NDM-5, and acquired resistance to tigecycline during tigecycline salvage therapy.
METHODS: Antimicrobial susceptibility testing, Southern blot hybridization, and complete genome sequence of the strains were carried out. The genetic characteristics of the mcr-1 and bla NDM-5 plasmids were analyzed. The whole genome sequencing of mcr-1-containing plasmid was completed. Finally, putative single nucleotide polymorphisms and deletion mutations in the tigecycline-resistant strain were predicted.
RESULTS: Three E. coli isolates were obtained from ascites, pleural effusion, and stool of a patient; they were resistant to almost all the tested antibiotics. The first two strains separated from ascites (E-FQ) and hydrothorax (E-XS) were susceptible to amikacin and tigecycline; however, the third strain from stool (E-DB) was resistant to tigecycline after nearly 3 weeks\' treatment with tigecycline. All three isolates possessed both mcr-1 and bla NDM-5. The bla NDM-5 gene was found on the IncX3 plasmid, whereas the mcr-1, fosA3 and blaCTX-M-14 were located on the IncHI2 plasmid. Mutations in acrB and lon were the reason for the resistance to tigecycline.
CONCLUSIONS: This is the first report of a colistin-, carbapenem-, and tigecycline-resistant E. coli in China. Tigecycline resistance acquired during tigecycline therapy is of great concern for us because tigecycline is a drug of last resort to treat carbapenem-resistant Gram-negative bacterial infections. Furthermore, the transmission of such extensively drug-resistant isolates may pose a great threat to public health.