Germination inhibition of Bacillus cereus spores: impact of the lipophilic character of inhibiting compounds

• Published in: International journal of food microbiology Vol. 160; no. 2; pp. 124 - 130
• Main Authors: van Melis, C.C.J., Almeida, C. Bravo, Kort, R., Groot, M.N. Nierop, Abee, T.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.11.2012; Elsevier
• Subjects: 1-alkanols; absorbance; acidification; Acids - metabolism; Alcohols; Alcohols - metabolism; atcc-14579; Bacillus cereus; Bacillus cereus - drug effects; Bacillus cereus - physiology; bacterial-spores; Biological and medical sciences; carbon; dormant; escherichia-coli; fluorescence; Food industries; Food Microbiology; Fundamental and applied biological sciences. Psychology; hexanoic acid; Hydrogen-Ion Concentration; hydrophobicity; Inhibition; inner membrane; lipid-bilayers; Lipophilicity; microorganisms; octanol-water partition coefficients; Organic acids; Picolinic Acids - metabolism; propionic acid; sorbic acid; Spore germination; spores; Spores, Bacterial - drug effects; Spores, Bacterial - physiology; Bacillus cereus; Inhibition; Spore germination; Organic acids; Lipophilicity; Alcohols; Bacillales; Germination; Bacteria; Alcohol; Bacillaceae; Spores
• ISSN: 0168-1605; 1879-3460
• DOI: 10.1016/j.ijfoodmicro.2012.10.006

In this study, the impact of a range of organic acids and structurally similar alcohols with three to six carbon backbones and increasing lipophilic character, were tested on the germination behavior of B. cereus ATCC 14579 spores. This approach allowed substantiating whether the effectivity of the various compounds was largely dictated by membrane interference or a classic weak acid acidification effect. The octanol–water partition coefficient (log Poct/water) ranges from 0.25/0.33 to 2.03/1.96 for propanol/undissociated propionic acid and hexanol/undissociated hexanoic acid, respectively. Performance of germination assays at neutral (pH7) and acidic conditions (pH5.5) allowed for a comparative analysis of the action of dissociated versus undissociated acids, and the presumed pH-independent effect of the corresponding alcohols. Germination assays, based on both continuously measured optical density and time-based plating experiments, and microscopic observations demonstrated the correlation between the lipophilic character of the selected compounds and their inhibiting effect on spore germination. Real-time fluorescence based assays showed that membrane integrity in dormant spores was maintained in the presence of the tested inhibitors. Lowering the critical concentration of inhibitors by a one-step washing procedure resulted in the onset of nutrient-induced germination, indicating the reversible nature of the inhibition process. Furthermore, blocking of nutrient-induced germination in the presence of inhibitory concentrations of selected lipophilic acids and corresponding alcohols was by-passed upon addition of Ca-dipicolinic acid, pointing to loss of signaling capacity in germinant receptor-mediated germination activity. These findings show that lipophilicity is an important determinant for the ability of the selected acids and corresponding alcohols to accumulate in the spore inner membrane and their ability to act as a germination-inhibitor. ► The impact of a range of organic acids and structurally similar alcohols was tested on Bacillus cereus spore germination. ► Lipohilicity is an important determinant for the ability of organic acids and alcohols to inhibit spore germination. ► Effectivity of the various compounds is largely dictated by spore membrane interference. ► Germination inhibition by accumulation of lipophilic compounds in the inner membrane is reversible and can be circumvented. ► Accumulation of short- to medium-chain lipophilic compounds in the inner membrane does not affect membrane integrity.