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Impacts of resistance gene knock-outs on the proteome

ABSTRACT: The spread of antibiotic resistance has developed to all known antibiotics. Extended spectrum β-lactamase-producing bacteria are particularly problematic, as they are resistant to a wide range of commonly used antibiotics. Resistance to β-lactams is known to be multifactorial, although the underlying mechanisms generally are poorly understood but critical factors for effective therapy against infections, especially for multi-resistant pathogenic bacteria. In the present study, a plasmid-based homologous recombination system was used to target and delete specific β-lactamase genes (i.e., the blaOXA-1, blaTEM-1 or the ESBL blaCTX-M15) of the clinical strain ESBL Escherichia coli CCUG 73778, generating three “knock-out” clone variants, each one lacking only one of the β-lactamases. The objective was to determine the genotypic impacts of each gene loss on the phenotypic antibiotic resistance and proteome of the bacterium. Quantitative proteomic analyses performed on the three clone variants and the original strain, using tandem mass tags (TMT) and bottom-up liquid chromatography tandem mass spectrometry (LC-MS/MS), after exposure to different concentrations of cefadroxil. Variation of the proteome in each clone variant was determined, to establish the relative importance of each resistance gene and better understand the genetic and proteomic responses and mechanisms of the resistance phenotypes. The knockout of blaCTX-M-15 was observed to have the greatest impact in protein expression, with the knockout of blaOXA-1 also effecting a marked but lower degree of changes. Proteins known to be associated with antibiotic resistance, cell membrane integrity, cellular stress, gene expression and hypothetical/unknown function proteins, among others, demonstrated distinct differences in expression levels (Fold change >1-5 or <-1.5), that may be related to aspects of compensation for the mutant resistance phenotypes. The present study provides a framework to study the impacts of targeted loss of antibiotic resistance genes in clinically relevant strains for understanding the mechanisms of phenotypic antibiotic resistance.

INSTRUMENT(S): Orbitrap Fusion Lumos

ORGANISM(S): Escherichia Coli

SUBMITTER: Proteomics Core Facility

LAB HEAD: Edward Moore

PROVIDER: PXD029140 | Pride | 2023-01-04

REPOSITORIES: Pride

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			Action	DRS
	3255_TMT_set1to4_3255ecoli_try_0miss_perc_norm_Lumos_191124.msf	Msf
	3255_TMT_set1to4_3255ecoli_try_0miss_perc_norm_Lumos_191124.pdResult	Other
	File_List.xlsx	Xlsx
	Lumos_191124_04.raw	Raw
	Lumos_191124_05.raw	Raw

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Project description:Escherichia coli (E. coli) urinary tract infections (UTIs) are becoming a serious problem both for pets and humans (zoonosis) due to the close contact and to the increasing resistance to antibiotics. Great progress has been made in the discovery of novel antibiotics to counteract E. coli pathogens. However, this huge progress has been undercut by the evolution of bacteria in the way of drug resistance. Enrofloxacin is one of the most efficient antibiotics against E. coli pathogens and there is considerable evidence that documents how this microorganism is becoming more resistant to this antibiotic and is developing multidrug resistance. This study has been performed in order to unravel the mechanism of induced enrofloxacin resistance in canine E. coli isolates that represent a good tool to study this pathology. For a comprehensive investigation about antibiotic resistance mechanisms, an E. coli isolate from urinary tract infection (UTI) was induced to grow under a concentration of 10 µg/ml of enrofloxacin. Proteins represent the main contributors to the mechanisms involved in antibiotic resistance in bacteria. Their abundance profile provides reliable information about the mechanisms involved in this process. Three biological replicates of control and resistant isolate have been analyzed both through 2D DIGE and shotgun proteomics. In our case, prior to perform the proteomics analysis, the screening with MS profiling of control and resistant isolates was performed highlighting the differences among strains and successfully clustering experimental strains according to PC analysis (PCA). The results clearly demonstrate differential profiles in peptide expression among clusters and between isolate and reference strain. According to these preliminary results, the protein profile of the resistant group was compared with the one of its sensitive counterpart by a proteomic analysis based on 2D-DIGE to separate proteins combined to MALDI MS analysis and database search to identify differentially expressed proteins. This analysis showed the modulation of 19 proteins between the two conditions. At the same time, another comparative proteomics investigation was also carried out by free-label nLC-MSE. This method has allowed the qualitative and quantitative analysis of total protein extracts of the two groups for the simultaneous screening of a larger number of proteins. A total of 57 differentially expressed proteins were identified and a comprehensive study on the proteins associated with enrofloxacin resistance was carried out. We classified these modulated proteins by their molecular functions and pathways where they are principally involved. This approach allowed to highlight some pathways that can be involved in an increased antibiotic resistance. Two major mechanisms were discovered. The first one was related to the stabilization of DNA structure through the up-regulation of Dsp protein. The second one was the downregulation of outer membrane protein W in order to reduce the membrane permeability to enrofloxacin. Discovered differentilally expressed proteins are principally involved in antibiotic resistance and linked to the oxidative stress response, to DNA protection and in membrane permeability. Moreover, since enrofloxacin is an inhibitor of DNA gyrase, the overexpression of DNA starvation/stationary phase protection protein (Dsp) could be a central point to discover the mechanism of this clone to counteract the effects of enrofloxacin. In parallel, the dramatic decrease of the synthesis of the outer membrane protein W, which represents one of the main gates for enrofloxacin entrance, could explain additional mechanism of E. coli defense against this antibiotic. The proteins differentially expressed could represent putative targets for the development of new strategies to counteract drug and multidrug resistance.

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Impacts of resistance gene knock-outs on the proteome

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