Effects of Subinhibitory Concentrations of Menthol on Adaptation, Morphological, and Gene Expression Changes in Enterohemorrhagic Escherichia coli

Abstract

Menthol (C 10 H 20 O) possesses antibacterial activity; nevertheless, bacterial adaptation to this compound has never been studied. Here we report that precultivation of enterohemorrhagic Escherichia coli (EHEC) strains in increasing subinhibitory (SI) concentrations of menthol significantly elevates (4-to 16-fold) their resistance to menthol. Concomitant morphological alterations included the appearance of mucoid colonies and reduced biofilm production. Scanning electron microscopy (SEM) examination revealed suppressed curli formation in menthol-adapted cells. Expression of the gene cpsB10 (encoding one of the enzymes responsible for colanic acid production) was elevated in response to SI concentrations of menthol in a laboratory E. coli strain, whereas expression in an rcsC null mutant was reduced, implicating a partial role for the Rcs phosphorelay system in mediating the menthol signal. Adaptation to menthol also reduced expression of the locus of enterocyte effacement-encoded regulator (Ler). This reduction, together with reduced curli and biofilm formation and elevated mucoidity, suggests a general reduction in bacterial virulence following adaptation to menthol. Our results thus suggest menthol as a potential lead in the recently emerging alternative strategy of targeting bacterial virulence factors to develop new types of anti-infective agents.

Antibacterial Activity of Carum copticum Essential Oil Against Escherichia Coli O157:H7 in Meat: Stx Genes Expression

“…multiflora Boiss EO diminishes the gene expressions of enterotoxins A, C, and B in a dosedependent manner. Similar results were also reported by Qiu et al [27], Landau and Shapira [21], and Husain et al [16] that explained exposure of S. aureus, EHEC, Pseudomonas aeruginosa, and Aeromonas hydrophila to subMICs concentrations of EOs, or their constituents reduce the expression of virulence factors. In another study, Harris et al [12] found that including 2 and 3 % salt in lactose broth decreased E. coli O157:H7 population, but increased stx2 expression compared to control (1 % salt).…”

“…Effects of EOs on virulence gene expression of pathogenic bacteria were investigated in broth or food-like broth models [8,21,25]. However, environmental conditions such as the type of food or other sample matrixes may have a significant effect on the virulence gene expression.…”

Effects of Menthol Supplementation in Feedlot Cattle Diets on the Fecal Prevalence of Antimicrobial-Resistant Escherichia coli

“…Previous studies have demonstrated inhibitory effects with concentrations of 75 mM for E . coli O157:H7 [27] and as low as 16 mM with E . coli ATCC15221 [28].…”

A Colanic Acid Operon Deletion Mutation Enhances Induction of Early Antibody Responses by Live Attenuated Salmonella Vaccine Strains

“…The CA-deficient E. coli strain had less viability in the human gastrointestinal tract environment and upon exposure to acid but not to bile (36). Most of this research on CA was carried out with E. coli strains (5), such as different laboratory K-12 strains, including MC4100, MG1655, and W3310 (6,8,17,30,31,(37)(38)(39)(40), K1 (41), K5 (41), K92 (42), extraintestinal isolate O4/K54/H5 (35,43), different O8 and O9 pathovars (44), enterohemorrhagic E. coli O157:H7 (18,26,27,36,37,45), and uropathogenic E. coli (33). Although it was reported that CA in Salmonella is not important for biofilm formation in vitro (46), some reports indicated that CA in Salmonella may play a role in vivo (4,47,48).…”