Antimicrobial resistance, molecular characteristics, virulence and pathogenicity of bla NDM-1-positive Enterobacter cloacae.

Introduction. The bla _NDM-1 -positive Enterobacter cloacae has led to limited therapeutic options for clinical treatment.Hypothesis/Gap Statement. Analysing the antimicrobial resistance and molecular typing of bla _NDM-1-positive E. cloacae is of great significance. Meanwhile, the effect of the bla _NDM-1 gene on the virulence and pathogenicity of E. cloacae remains unclear and should be assessed.Aim. To understand bla _NDM-1-positive E. cloacae from different perspectives.Methodology. The PCR was used to screen bla _NDM-1-positive E. cloacae, then, antimicrobial susceptibility tests and multilocus sequence typing (MLST) were performed on them; sixty-nine strains of bla _NDM-1-negative E. cloacae were collected as the controls, 28 pairs of virulence-related genes' carriage and biofilm-forming ability were detected for preliminary evaluation of the virulence phenotype of the strains; to gain insight into the effect of the bla _NDM-1 gene on the virulence and pathogenicity of E. cloacae, the bla _NDM-1-positive E. cloacae T2 (NDM-1), the T2 bla _NDM-1 knockout strain (ΔNDM-1) and ATCC13047 (ST) were studied, compared the motility, anti-serum killing ability, and virulence to cells. Then, the mice intraperitoneal infection model was established, the survival curve, histopathological characteristics, bacterial load in spleen and the contents of cytokines were compared.Results. (1) Thirty-five bla _NDM-1-positive E. cloacae exhibited multidrug resistance. MLST distinguished 12 STs, ST74 was the most common clonal type (11/35), followed by ST114 (10/35). (2) The detection rates of virulence genes clpB, icmf, VasD/Lip and acrA in the bla _NDM-1-positive E. cloacae were significantly higher than those in bla _NDM-1-negative E. cloacae (P<0.05), while there was no significant difference in the amount of biofilm formation between two groups. (3) The presence of bla _NDM-1 gene attenuated the motility diameter of E. cloacae, but had no significant effect on their ability to resist serum killing, and the virulence to cells. The survival rate, histopathological changes, bacterial load in spleen and inflammatory cytokines were not significantly affected.Conclusions. (1) The bla _NDM-1-positive E. cloacae exhibited multidrug resistance, and the MLST typing was mainly ST74 and ST114, with a small-scale clonal spread of the ST114 strain in the hospital NICU ward. (2) The bla _NDM-1 gene did not affect the virulence and pathogenicity of E. cloacae.