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Objective: To observe the effect of the (p)ppGpp synthase gene (relA) on the heteroresistance of colistin against Acinetobacter baumannii. Methods: The relA gene in Acinetobacter baumannii ATCC19606 was knocked out by Red homologous recombination technique. The biofilm formation of Acinetobacter baumannii was observed by crystal violet staining. The change of heterogeneous colonies of Acinetobacter baumannii under the action of colistin was detected by population analysis profiles (PAP) and the heterogeneity was calculated. The killing curve was used to detect the formation of persistent bacteria in Acinetobacter baumannii under the action of colistin. Results: The relA gene in Acinetobacter baumannii was successfully knocked out, and the relA knockout strain ATCC19606-ΔrelA was obtained. After relA gene knockout, the biofilm formation of Acinetobacter baumannii decreased significantly. After relA gene knockout, Acinetobacter baumannii significantly reduced the heterogeneous colonies and persistent bacteria formation under the action of colistin. Conclusion: The bacterial stringent reaction (p) ppGpp synthase relA may be an important factor affecting the heteroresistance of Acinetobacter baumannii to colistin.
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Objective To construct a blaNDM-1gene deletion mutant of Enterobacter cloacae and to analyze its biological characteristics. Methods The blaNDM-1gene deletion mutant was constructed by using Red homologous recombination technology and verified by PCR and RT-qPCR. Antimicrobial susceptibility profiles,growth curves and in vitro competition abilities of the original strain and the blaNDM-1gene deletion mutant were analyzed. Results PCR,DNA sequencing and RT-qPCR showed that the blaNDM-1gene dele-tion mutant was successfully constructed. Antimicrobial susceptibility test showed that the original strain was resistant to imipenem,meropenem and ertapenem, while the blaNDM-1gene deletion mutant was sensitive to all. The original strain and the blaNDM-1gene deletion mutant had similar growth curves in Luria-Bertani liq-uid medium. In vitro competition experiment revealed that the competitive index of them was 0.69. Conclu-sion Red homologous recombination technology can be used to knockout the blaNDM-1gene of Enterobacter cloacae,which is associated with antimicrobial resistance and competitiveness.
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Objective To construct small RNA deletion and overexpression strains with a length of less than 100 nt in Yersinia pestis.Methods Deletion mutants of the target sRNAs were constructed by increasing the length of homologous regions.Meanwhile, the high copy plasmid pBAD/HisA was modified into an inducible transcriptional vector as an sRNA-overexpression plasmid by using QuikChange lightning site-directed mutagenesis kit .The presence , size, and transcription-al initiation sites of the indicated sRNA were predicted by transcriptome sequencing , primer extension , and previous stud-ies.The full-length DNA fragments of target sRNAs were transformed into the transcriptional vector .The overexpressing strains of sRNAs were identified by Northern Blot .Results and Conclusion Four sRNAs deletion mutants of sR01, sR02, sR03 and HmsA and three sRNAs overexpression mutants MicF , HmsA and CpxQ were successfully constructed .A method of construction of sRNA deficient and overexpressing strains of Y.pestis has been quickly and efficiently established by λ-Red homologous recombination technology and QuikChange ? lightning site-directed mutagenesis kit.
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Objective To construct Escherichia coli O157∶H7 T3SS effector NleF gene knockout mutant and its com-plementary strain, and probe its effects on bacterial growth and cell death .Methods T3SS Effector NleF gene knockout mutant ΔnleF was constructed with λ-Red homologous recombination .Complementary strain ΔnleF/NleF was constructed by transferring pET-24a(+)-NleF into ΔnleF competent cells.Wild type,ΔnleF and ΔnleF/NleF were cultured in LB and DMEM(10%FBS) respectively,D600 was measured every hour , and the growth curve was drawn .HeLa cells were infected with three kinds of strains , the supernatant of LDH release was detected with cytotoxicity detection kit ,and the cytotoxicity was calculated .Results ΔnleF and ΔnleF/NleF were constructed .The growth rates of wild type , ΔnleF and ΔnleF/NleF was not significantly different .Wild type O157 infection induced cell death .Cytotoxicity was increased as much in ΔnleF in-fected cells as in ΔnleF/NleF infected cells.Conclusion EHEC O157∶H7 T3SS Effector NleF has no significant effect on bacterial growth ,but might inhibit host cell death caused by bacterial infection .