Mechanisms of resistance to linalool in Salmonella Senftenberg and their role in survival on basil

Abstract

Fresh produce contaminated with human pathogens raises vital and ecological questions about bacterial survival strategies. Such occurrence was basil harboring Salmonella enterica serovar Senftenberg that caused an outbreak in 2007. This host was unanticipated due to its production of antibacterial substances, including linalool. We show that linalool perforates bacterial membranes, resulting in increased permeability and leakage of vital molecules. It also inhibits cell motility and causes bacterial aggregation. Linalool-resistance was investigated by identification and characterization of S. Senftenberg mutants that perform altered resistance. Resistance mechanisms include selective permeability, regulated efflux/influx and chemotaxis-controlled motility. Moreover, survival of S. Senftenberg on basil leaves was substantially affected by McpL, a putative chemotaxis-related receptor, and RfaG, a component of the lipopolysaccharide production pathway, both have a role in resistance to linalool. Results reveal that adaptation to linalool occurs in nature by concurrent mechanisms. This adaption raises concerns about pathogens adaptation to new hosts including antimicrobial-compound-producing plants.

Adaptation of Salmonella enterica Serovar Senftenberg to Linalool and Its Association with Antibiotic Resistance and Environmental Persistence

“…It was shown that linalool perforates the bacterial membrane of Gram-negative bacteria, resulting in the increased permeability of both membranes and the leakage of vital molecules (16). Linalool also directly or indirectly inhibits cell motility and causes bacterial aggregation in Salmonella enterica serovar Senftenberg by an unknown mechanism (16,17). The MIC of linalool against pathogens like Escherichia coli, Salmonella enterica, Staphylococcus spp., and Streptococcus spp.…”

“…typically ranges from 0.6 to 125 mM (17,18). However, much of the commercial use of linalool involves preparations with unspecified concentrations of linalool which may fall into its sublethal dosage range and, hence, provide considerable opportunity for bacterial adaptation to linalool (higher MIC values) when other barriers to bacteria applied in the product are not sufficient to eliminate the pathogens (16). For example, commercial fruit juices contain 0.02 to 90 mM linalool (19), and pet feed may contain up to 0.6 mM linalool (20).…”

“…The naturally reduced susceptibility of S. Senftenberg to EO components highlights the great health risks posed by the emergence of resistant pathogens adapted to plant-derived antimicrobial agents. Specifically, the resistance of S. Senftenberg to linalool is attributed to concurrent mechanisms, including chemotaxis-controlled motility, the selective permeability of the cell envelope, and regulated efflux/influx (16). The ability to form larger aggregates in the presence of linalool was also described, but its association with resistance is still unclear (16).…”

“…Specifically, the resistance of S. Senftenberg to linalool is attributed to concurrent mechanisms, including chemotaxis-controlled motility, the selective permeability of the cell envelope, and regulated efflux/influx (16). The ability to form larger aggregates in the presence of linalool was also described, but its association with resistance is still unclear (16). It was shown that exposure to linalool enhances the transcription of mcpL, an STM1657-like gene, in S. Senftenberg.…”

“…It was shown that exposure to linalool enhances the transcription of mcpL, an STM1657-like gene, in S. Senftenberg. This gene encodes a putative methylaccepting chemotaxis protein (MCP) with serine sensor receptors (16) which is possibly involved in the detection of chemotactic signals (31). Deletion of this gene in S. Senftenberg increases its sensitivity to linalool (16).…”