Background
Polymyxin B is considered a last-line therapeutic option against multidrug-resistant gram-negative bacteria, especially in COVID-19 coinfections or other serious infections. However, the risk of antimicrobial resistance and its spread to the environment should be brought to the forefront.
Methods
Pandoraea pnomenusa M202 was isolated under selection with 8 mg/L polymyxin B from hospital sewage and then was sequenced by the PacBio RS II and Illumina HiSeq 4000 platforms. Mating experiments were performed to evaluate the transfer of the major facilitator superfamily (MFS) transporter in genomic islands (GIs) to Escherichia coli 25DN. The recombinant E. coli strain Mrc-3 harboring MFS transporter encoding gene FKQ53_RS21695 was also constructed. The influence of efflux pump inhibitors (EPIs) on MICs was determined. The mechanism of polymyxin B excretion mediated by FKQ53_RS21695 was investigated by Discovery Studio 2.0 based on homology modeling.
Results
The MIC of polymyxin B for the multidrug-resistant bacterial strain P. pnomenusa M202, isolated from hospital sewage, was 96 mg/L. GI-M202a, harboring an MFS transporter-encoding gene and conjugative transfer protein-encoding genes of the type IV secretion system, was identified in P. pnomenusa M202. The mating experiment between M202 and E. coli 25DN reflected the transferability of polymyxin B resistance via GI-M202a. EPI and heterogeneous expression assays also suggested that the MFS transporter gene FKQ53_RS21695 in GI-M202a was responsible for polymyxin B resistance. Molecular docking revealed that the polymyxin B fatty acyl group inserts into the hydrophobic region of the transmembrane core with Pi-alkyl and unfavorable bump interactions, and then polymyxin B rotates around Tyr43 to externally display the peptide group during the efflux process, accompanied by an inward-to-outward conformational change in the MFS transporter. Additionally, verapamil and CCCP exhibited significant inhibition via competition for binding sites.
Conclusions
These findings demonstrated that GI-M202a along with the MFS transporter FKQ53_RS21695 in P. pnomenusa M202 could mediate the transmission of polymyxin B resistance.
This study investigated oxidative damage and exocrine dysfunction of fetal pancreas caused by maternal nutritional restriction. Eighteen ewes carrying singleton fetus were randomly divided into control group (CG, ad libitum, 0.67 MJ ME/BW 0.75 /d, n = 6), restricted group 1 (RG1, 0.33 MJ ME/BW 0.75 /d, n = 6), and restricted group 2 (RG2, 0.18 MJ ME/BW 0.75 /d, n = 6) at d 90 of pregnancy. Maternal undernutrition was imposed from d 90 to 140 of pregnancy. At 140 d of gestation, fetal blood and pancreas tissue were collected to determine fetal pancreatic extracellular matrix, antioxidant capacity, and indicators of exocrine dysfunction. With the decrease of maternal nutrition, the fetal body weight, pancreatic weight, and DNA content were reduced in RG2 compared with CG, and increased and thickened collagen fibers were observed in RG2. Fetuses in RG2 exhibited increased collagen 3 (COL3) and fibronectin (FN) levels relative to CG, and the COL1:COL3 ratio was lower than that of the CG. For RG1, we found increased COL3 compared with CG. Malondialdehyde, serum amylase, and serum lipase in fetal pancreas in RG2 increased, but the total antioxidant capacity (T-AOC) decreased compared with the CG. The impaired ovine fetal pancreas growth, antioxidant imbalance, and pancreatic exocrine dysfunction are induced by maternal undernutrition during late pregnancy.
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