Co-Production of NDM-1 and OXA-10 ß-Lactamase in Citrobacter braakii Strain Causing Urinary Tract Infection.

In this study, we describe, for the first time, the co-existence of bla NDM-1and bla OXA-10 in a carbapenem-resistant Citrobacter braakii strain DY2019 isolated from a patient with urinary tract infection in China. We aimed to investigate the genomic context of two ß-lactamase-producing plasmids and characterize the transmission mechanism of the carbapenemase-encoding gene. Whole-genome sequencing of strain DY2019 was performed with Nanopore and Illumina platforms, which revealed a chromosome sequence with the length of 4,830,928 bp, an IncC group plasmid pDY2019-OXA (size of 178,134 bp), and a novel IncHI2 group plasmid pDY2019-NDM (length 348,495 bp). A total of 16 antimicrobial resistance genes (ARGs) that confer resistance to nine different antibiotic groups were identified in strain DY2019, and 11 of them were carried by plasmid pDY2019-OXA. These data and analyses suggest that the carbapenem-resistant C. braakii strains may serve as potential reservoir of carbapenemase and highlight the need for further close surveillance of this species in clinical settings.

How do mutations affect the structural characteristics and substrate binding of CYP21A2? An investigation by molecular dynamics simulations.

Congenital adrenal hyperplasia (CAH) is one of the most frequent inborn errors of metabolism, inherited as an autosomal recessive trait. Above 95% of CAH cases are caused by mutations in cytochrome P450 21A2 (CYP21A2). It is a pity that how these mutations affect the structural characteristics and substrate binding of CYP21A2 is still unclear. To this end, molecular dynamics (MD) simulations and binding free energy calculations are performed to investigate the effects of single point mutations (L108R, G292C, G292S, G293D, and T296N) in CYP21A2. The results indicate that mutations could cause the local conformational changes of CYP21A2, affecting the substrate binding by changing the interaction between the protein and heme, changing the charge environment of residues, or introducing steric hindrance. In addition, our work gives a wonderful explanation of the phenomenon that though the substrate binding ability increases, the reaction activity decreases in T296N. The present study provides detailed atomistic insights into the structure-function relationships of CYP21A2, which could contribute to further understanding about 21-hydroxylase deficiency and also provide a theoretical basis for CAH prediction and treatment.