Quinolone-resistant gyrase mutants demonstrate decreased susceptibility to triclosan

Objectives: Cross-resistance between antibiotics and biocides is a potentially important driver of MDR. A relationship between susceptibility of Salmonella to quinolones and triclosan has been observed. This study aimed to: (i) investigate the mechanism underpinning this; (ii) determine whether the phenotype is conserved in Escherichia coli; and (iii) evaluate the potential for triclosan to select for quinolone resistance. Methods: WT E. coli, Salmonella enterica serovar Typhimurium and gyrA mutants were used. These were characterized by determining antimicrobial susceptibility, DNA gyrase activity and sensitivity to inhibition. Expression of stress response pathways (SOS, RpoS, RpoN and RpoH) was measured, as was the fitness of mutants. The potential for triclosan to select for quinolone resistance was determined. Results: All gyrase mutants showed increased triclosan MICs and altered supercoiling activity. There was no evidence for direct interaction between triclosan and gyrase. Identical substitutions in GyrA had different impacts on supercoiling in the two species. For both, there was a correlation between altered supercoiling and expression of stress responses. This was more marked in E. coli, where an Asp87Gly GyrA mutant demonstrated greatly increased fitness in the presence of triclosan. Exposure of parental strains to low concentrations of triclosan did not select for quinolone resistance. Conclusions: Our data suggest gyrA mutants are less susceptible to triclosan due to up-regulation of stress responses. The impact of gyrA mutation differs between E. coli and Salmonella. The impacts of gyrA mutation beyond quinolone resistance have implications for the fitness and selection of gyrA mutants in the presence of non-quinolone antimicrobials

Lipid A modifications in Bordetella pertussis : regulation and function of the lgm locus

In many Gram-negative pathogens, gene transcription is often facilitated by post-transcriptional regulatory mechanisms. In Bordetella pertussis, several regulatory RNAs have been identified, but their targets and impacts on virulence factor production have not been assessed. RNase III and RNase E, endonucleases with dominant roles in regulatory RNA processing, were mutated in B. pertussis to determine gene loci regulated at the post-transcriptional level. RNA-Seq analysis of these strains identified that ~25% of the B. pertussis transcriptome was affected in each endonuclease mutant. Substantial impacts were observed on genes associated with amino acid uptake, bacterial secretion, and many virulence factors. Comparing these findings to the regulon of the RNA chaperone Hfq, 120 genes, and 19 operons were identified as potentially influenced at the post-transcriptional level. Amongst these, the lipid A glucosamine modification (lgm) locus was one of the most upregulated gene loci in the RNase E mutant strain. The lgm locus is a 5 gene operon consisting of four genes in one orientation (lgmA-D) and a fifth open reading frame (lgmE) overlapping in the opposite orientation. Given lipid A modifications in Gram-negative bacteria are typically controlled by complex regulatory networks, it was proposed that several overlapping systems are involved in lgm locus regulation, including the role of a cis-encoded antisense RNA. As shown by luciferase reporter assays, the lgm locus responds to Bvg phase, nutrient availability, low pH, and increased C02%. These assays also identified a reciprocal relationship in activation of the diametrically opposed lgmA and lgmE promoters, suggestive of asRNA regulation. It was then proposed that lgmE acts as dual-function RNA as the lgmE ORF has all the characteristics of a translated protein. It is shown that lgmE encodes a functional, small membrane-associated protein, and deletion and overexpression of lgmE negatively impact lgm locus activity. Furthermore, structural predictions and modelling of protein-protein interactions suggest LgmE may form a membrane anchor for localization with LgmB. Overall, the lgm locus forms a non-contiguous operon whose activity is modulated at the transcriptional, post-transcriptional, and post-translational levels, with these integrated mechanisms intersecting as a means to fine-tune lipid A modification in B. pertussis.Science, Faculty ofMicrobiology and Immunology, Department ofGraduat

Optimised Heterologous Expression and Functional Analysis of the Yersinia pestis F1-Capsular Antigen Regulator Caf1R

The bacterial pathogen, Yersinia pestis, has caused three historic pandemics and continues to cause small outbreaks worldwide. During infection, Y. pestis assembles a capsule-like protective coat of thin fibres of Caf1 subunits. This F1 capsular antigen has attracted much attention due to its clinical value in plague diagnostics and anti-plague vaccine development. Expression of F1 is tightly regulated by a transcriptional activator, Caf1R, of the AraC/XylS family, proteins notoriously prone to aggregation. Here, we have optimised the recombinant expression of soluble Caf1R. Expression from the native and synthetic codon-optimised caf1R cloned in three different expression plasmids was examined in a library of E. coli host strains. The functionality of His-tagged Caf1R was demonstrated in vivo, but insolubility was a problem with overproduction. High levels of soluble MBP-Caf1R were produced from codon optimised caf1R. Transcriptional-lacZ reporter fusions defined the PM promoter and Caf1R binding site responsible for transcription of the cafMA1 operon. Use of the identified Caf1R binding caf DNA sequence in an electrophoretic mobility shift assay (EMSA) confirmed correct folding and functionality of the Caf1R DNA-binding domain in recombinant MBP-Caf1R. Availability of functional recombinant Caf1R will be a valuable tool to elucidate control of expression of F1 and Caf1R-regulated pathophysiology of Y. pestis.Science, Faculty ofNon UBCMicrobiology and Immunology, Department ofReviewedFacult