Antimicrobial chemicals are widely applied to clean and disinfect food-contacting surfaces. However, the cellular response of bacteria to various disinfectants is unclear. In this study, the physiological and genome-wide transcriptional responses of Bacillus cereus ATCC 14579 exposed to four different disinfectants (benzalkonium chloride, sodium hypochlorite, hydrogen peroxide, and peracetic acid) were analyzed. For each disinfectant, concentrations leading to the attenuation of growth, growth arrest, and cell death were determined. The transcriptome analysis revealed that B. cereus, upon exposure to the selected concentrations of disinfectants, induced common and specific responses. Notably, the common response included genes involved in the general and oxidative stress responses. Exposure to benzalkonium chloride, a disinfectant known to induce membrane damage, specifically induced genes involved in fatty acid metabolism. Membrane damage induced by benzalkonium chloride was confirmed by fluorescence microscopy, and fatty acid analysis revealed modulation of the fatty acid composition of the cell membrane. Exposure to sodium hypochlorite induced genes involved in metabolism of sulfur and sulfur-containing amino acids, which correlated with the excessive oxidation of sulfhydryl groups observed in sodium hypochlorite-stressed cells. Exposures to hydrogen peroxide and peracetic acid induced highly similar responses, including the upregulation of genes involved in DNA damage repair and SOS response. Notably, hydrogen peroxide-and peracetic acid-treated cells exhibited high mutation rates correlating with the induced SOS response.

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An association between swarming and hemolysin BL secretion was observed in a collection of 42 Bacillus cereus isolates (P ‫؍‬ 0.029). The highest levels of toxin were detected in swarmers along with swarm cell differentiation (P ‫؍‬ 0.021), suggesting that swarming B. cereus strains may have a higher virulence potential than nonswarming strains.Bacterial swarming is a specialized form of surface translocation that enables flagellate bacteria to coordinately move atop solid surfaces (11). The ability to swarm depends on a complex differentiation process that leads short and oligoflagellate swimmer cells to produce long, multinucleate, and hyperflagellate swarm cells actively migrating over surfaces in organized groups of tightly bound cells (reviewed in reference 10). The widespread nature of swarming-proficient species suggests that this type of flagellum-aided motility is a successful strategy developed by flagellate bacteria to rapidly colonize environmental surfaces (10). Moreover, swarming can be influential in host-pathogen interactions, since it contributes to the virulence potential that certain pathogens may exert by facilitating host colonization (1,7,8,14) and/or leads to an increase in the production of specific virulence factors (2, 15). We have previously described the swarming behavior exhibited by laboratory strains of Bacillus cereus and Bacillus thuringiensis (9, 19), two closely related species that produce common genome-encoded virulence factors (17); among these, the tripartite toxin (B, L 1 , and L 2 components) hemolysin BL (HBL) exerts enterotoxic, hemolytic, cytotoxic, and dermonecrotic activity (3-5). In B. thuringiensis 407 Cry Ϫ , a mutation in flhA, a component of the flagellar export apparatus (12, 16), was found to coordinately abolish swarming and secretion of HBL (9). In B. cereus NCIB 8122, which produces only the L 2 component of HBL, L 2 secretion was detectable exclusively in differentiated swarm cells (19). These findings suggested that swarming and HBL secretion could be associated phenomena.In this study, we assessed the motility behavior of and the secretion of HBL by B. cereus strains isolated from different sources to evaluate whether (i) HBL secretion requires intact flagella, (ii) swarming and HBL secretion are prevalent traits in natural isolates, and (iii) an increase in HBL secretion occurs along with swarm cell differentiation.Swimming and swarming motility in B. cereus isolates. B. cereus strains were collected from clinical, environmental, or food samples (Table 1) and identified by the API 50 CH assay (Bio-Merieux, France). Identification of B. cereus was confirmed, excluding the presence of parasporal crystals, which are discriminative for B. thuringiensis, in preparations of sporulating cultures stained with 0.5% basic fuchsin. Assays for swimming (on 1% tryptone-0.5% NaCl plates containing 0.25% agar [TrM]) and chemotaxis (on TrM supplemented with 2.0 mM mannitol or glutamine) were performed as described previously (9, 19). Swarming differentiation (on 1% try...

ABSTRACTMulticellular communities produced byBacillus subtiliscan adopt sliding or swarming to translocate over surfaces. While sliding is a flagellum-independent motility produced by the expansive forces in a growing colony, swarming requires flagellar functionality and is characterized by the appearance of hyperflagellated swarm cells that associate in bundles or rafts during movement. Previous work has shown that swarming by undomesticatedB. subtilisstrains requiresswrA, a gene that upregulates the expression of flagellar genes and increases swimming motility, and surfactin, a lipopeptide biosurfactant that also facilitates sliding. Through an analysis ofswrA+andswrAmutant laboratory strains with or without a mutation insfp(a gene involved in surfactin production), we show that bothswrAand surfactin upregulate the transcription of the flagellin gene and increase bacterial swimming. Surfactin also allows the nonswarmingswrAmutant strain to efficiently colonize moist surfaces by sliding. Finally, we reconfirm the essential role ofswrAin swarming and show that surfactin, which increases surface wettability, allowsswrA+strains to produce swarm cells on media at low humidity.