Evolution of carbapenem resistance in klebsiella pneumoniae and escherichia coli carrying blaNDM-1 gene: imipenem exposure results in sustained resistance memory of strains in vitro

Background Antibiotics exert an outstanding selective pressure on bacteria, forcing their chromosomal gene mutations and drug resistance genes to spread. The objective of this study is to evaluate the expression of the New Delhi Metallo-beta-Lactamase-1 gene (bla(NDM-1)) in the clinical isolate (Klebsiella pneumoniae TH-P12158), transformant strains Escherichia coli BL21 (DE3)-bla(NDM-1), and Escherichia coli DH5 alpha-bla(NDM-1) when exposed to imipenem. Methods beta-Lactamase genes (bla(SHV,) bla(TEM-1), bla(CTX-M-9), bla(IMP), bla(NDM-1), bla(KPC), bla(OXA), bla(GES), and bla(DHA)) from randomly selected carbapenems-sensitive K.pneumoniae (n = 20) and E.coli (n = 20) strains were amplified by PCR. The recombinant plasmid of pET-28a harboring bla(NDM-1) was transformed into E.coli BL21 (DE3) and E.coli DH5 alpha by electroporation. The resistance phenotype and higher bla(NDM-1) expression in K.pneumoniae TH-P12158, transformant E.coli BL21 (DE3)-bla(NDM-1), and E.coli DH5 alpha-bla(NDM-1) were observed when exposed to imipenem with grade increasing, decreasing, and canceling doses, respectively. Results After being exposed to different doses of imipenem, the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of antimicrobial drugs and blaNDM-1 expression of strains increased, which was positively correlated with doses of imipenem. On the contrary, with the decrease or cancellation of imipenem doses, the blaNDM-1 expression was deteriorated, while the MIC and MBC values remained relatively stable. These results demonstrated that low doses of imipenem (<MIC) could press blaNDM-1 positive strains producing stable drug resistance memory and altered blaNDM-1 expression. Conclusions Low doses of imipenem could press bla(NDM-1) positive strains producing sustained resistance memory and altered bla(NDM-1) expression. In particular, the positive correlation between the resistance genes expression and antibiotics exposure shows promising guiding significance for clinical medication.