Interspecies Comparison of the Bacterial Response to Allicin Reveals Species‐Specific Defense Strategies

Abstract

Allicin, a broad‐spectrum antimicrobial agent from garlic, disrupts thiol and redox homeostasis, proteostasis, and cell membrane integrity. Since medicine demands antimicrobials with so far unexploited mechanisms, allicin is a promising lead structure. While progress is being made in unraveling its mode of action, little is known on bacterial adaptation strategies. Some isolates of Pseudomonas aeruginosa and Escherichia coli withstand exposure to high allicin concentrations due to as yet unknown mechanisms. To elucidate resistance and sensitivity‐conferring cellular processes, the acute proteomic responses of a resistant P. aeruginosa strain and the sensitive species Bacillus subtilis are compared to the published proteomic response of E. coli to allicin treatment. The cellular defense strategies share functional features: proteins involved in translation and maintenance of protein quality, redox homeostasis, and cell envelope modification are upregulated. In both Gram‐negative species, protein synthesis of the majority of proteins is downregulated while the Gram‐positive B. subtilis responded by upregulation of multiple regulons. A comparison of the B. subtilis proteomic response to a library of responses to antibiotic treatment reveals 30 proteins specifically upregulated by allicin. Upregulated oxidative stress proteins are shared with nitrofurantoin and diamide. Microscopy‐based assays further indicate that in B. subtilis cell wall integrity is impaired.

Genetic and molecular characterization of multicomponent resistance ofPseudomonasagainst allicin

“…The garlic defense substance allicin is a potent thiol reagent which targets the cellular redox buffer glutathione and accessible -SH groups in proteins (Borlinghaus et al, 2014). Allicin has been shown to S-thioallylate several cysteine-containing proteins in bacteria (Müller et al, 2016;Chi et al, 2019;Loi et al, 2019;Wüllner et al, 2019) and humans (Gruhlke et al, 2019) and has been described as a redox toxin (Gruhlke et al, 2010). S-thioallylation by allicin is reversible and sublethal doses suppress bacterial multiplication for a period of time, the length of which is dose-dependent, before growth resumes (Müller et al, 2016).…”

“…There are indications that the allicin target and cellular redox buffer glutathione (GSH) plays a central role in enabling cells to resist the effects of allicin (Gruhlke et al, 2010(Gruhlke et al, , 2017Leontiev et al, 2018). Allicin reversibly Sthioallylates a range of proteins in bacteria and human cells which can lead to loss of function of essential enzymes (Müller et al, 2016;Chi et al, 2019;Gruhlke et al, 2019;Loi et al, 2019;Wüllner et al, 2019).…”

Allicin, the Odor of Freshly Crushed Garlic: A Review of Recent Progress in Understanding Allicin’s Effects on Cells

“…This was demonstrated with an rpoH mutant which was not able to induce the heat shock response, and unlike the wild type was unable to recover from allicin treatment [31]. Additionally, allicin also induced oxidative stress response genes controlled by the OxyR and PerR regulons, e.g., katA, ahpCF, and thioredoxins in B. subtilis, E. coli, and S. aureus [31,59,60,78].…”

“…Likewise, the CtsR and HrcA controlled regulons encoding Clp proteases and DnaK/GroESL chaperones were highly induced in the transcriptomes of B. subtilis and S. aureus [59,60]. Similarly, oxidative unfolding of proteins by allicin was countered by the induction of amino acid biosynthesis genes, ribosomal proteins, and translation factors in several bacteria tested [31,59,60,78,79]. It was shown that the ability to induce the heat shock response in E. coli was essential to overcome the effects of allicin stress.…”

A How-To Guide for Mode of Action Analysis of Antimicrobial Peptides

“…These proteins reflect the acute stress response of the bacterial cells to the given stress condition and are indicative of the antibiotic mechanism of action. A reference compendium with protein expression profiles of over 100 antimicrobial compounds has been established to aid mode of action analysis of new drug candidates (Bandow et al, 2003;Wenzel et al, , 2012Wenzel et al, , 2013Wenzel et al, , 2014Wenzel et al, , 2015bRaatschen et al, 2013;Stepanek et al, 2016a,b;Müller et al, 2016b;Scheinpflug et al, 2017;Saising et al, 2018;Meier et al, 2019;Wüllner et al, 2019). Radioactive 2D-PAGE should not be confused with two-dimensional difference gel electrophoresis (2D-DIGE), which also compares protein expression profiles by densitometric quantification against a control sample, but is a fluorescent sample multiplexing and not a metabolic labeling technique (Minden, 2012).…”