Loss of Function in Escherichia coli Exposed to Environmentally Relevant Concentrations of Benzalkonium Chloride

Forbes, Sarah; Morgan, Nicola; Humphreys, Gavin J.; Amézquita, Alejandro; Mistry, Hitesh; McBain, Andrew J.

Abstract

Assessing the risk of resistance associated with biocide exposure commonly involves exposing microorganisms to biocides at concentrations close to the MIC. With the aim of representing exposure to environmental biocide residues, Escherichia coli MG1655 was grown for 20 passages in the presence or absence of benzalkonium chloride (BAC) at 100 ng/liter and 1,000 ng/liter (0.0002% and 0.002% of the MIC, respectively). BAC susceptibility, planktonic growth rates, motility, and biofilm formation were assessed, and differentially expressed genes were determined via transcriptome sequencing. Planktonic growth rate and biofilm formation were significantly reduced (P < 0.001) following BAC adaptation, while BAC minimum bactericidal concentration increased 2-fold. Transcriptomic analysis identified 289 upregulated and 391 downregulated genes after long-term BAC adaptation compared with the respective control organism passaged in BAC-free medium. When the BAC-adapted bacterium was grown in BAC-free medium, 1,052 genes were upregulated and 753 were downregulated. Repeated passage solely in biocide-free medium resulted in 460 upregulated and 476 downregulated genes compared with unexposed bacteria. Long-term exposure to environmentally relevant BAC concentrations increased the expression of genes associated with efflux and reduced the expression of genes associated with outer-membrane porins, motility, and chemotaxis. This was manifested phenotypically through the loss of function (motility). Repeated passage in a BAC-free environment resulted in the upregulation of multiple respiration-associated genes, which was reflected by increased growth rate. In summary, repeated exposure of E. coli to BAC residues resulted in significant alterations in global gene expression that were associated with minor decreases in biocide susceptibility, reductions in growth rate and biofilm formation, and loss of motility.

Citation

Forbes, S., Morgan, N., Humphreys, G. J., Amézquita, A., Mistry, H., & McBain, A. J. (2019). Loss of Function in Escherichia coli Exposed to Environmentally Relevant Concentrations of Benzalkonium Chloride. Applied and Environmental Microbiology, 85(4), https://doi.org/10.1128/aem.02417-18

• Journal Article Type: Article
• Publication Date: Feb 15, 2019
• Deposit Date: Mar 11, 2024
• Journal: Applied and Environmental Microbiology
• Print ISSN: 0099-2240
• Electronic ISSN: 1098-5336
• Publisher: American Society for Microbiology
• Peer Reviewed: Peer Reviewed
• Volume: 85
• Issue: 4
• DOI: https://doi.org/10.1128/aem.02417-18
• Keywords: Ecology; Applied Microbiology and Biotechnology; Food Science; Biotechnology