Effects of Allicin on the Formation of Pseudomonas aeruginosa Biofilm and the Production of Quorum-Sensing Controlled Virulence Factors

The Gram-negative Pseudomonas aeruginosa bacterial pathogen is reputed for its resistance to multiple antibiotics, and this property is strongly associated with the development of biofilms. Bacterial biofilms form by aggregation of microorganisms on a solid surface and secretion of an extracellular polysaccharide substances that acts as a physical protection barrier for the encased bacteria. In addition, the P aeruginosa quorum-sensing system contributes to antibiotic resistance by regulating the expression of several virulence factors, including exotoxin A, elastase, pyoverdin and rhamnolipid. The organosulfur compound allicin, derived from garlic, has been shown to inhibit both surface-adherence of bacteria and production of virulence factors. In this study, the effects of allicin on P aeruginosa biofilm formation and the production of quorum-sensing controlled virulence factors were investigated. The results demonstrated that allicin could inhibit early bacterial adhesion, reduce EPS secretion, and down-regulate virulence factors' production. Collectively, these findings suggest the potential of allicin as a therapeutic agent for controlling P aeruginosa biofilm.

Selective retention in saline ice of extracellular polysaccharides produced by the cold-adapted marine bacteriumColwellia psychrerythraeastrain 34H

The retention of salts in laboratory-grown ice was compared to the retention of extracellular polysaccharide substances (EPS) produced by the cold-adapted marine gammaproteobacterium,Colwellia psychrerythraeastrain 34H. Saline ice was formed, by means of a cold-finger apparatus, from artificial sea-water solutions containing either native dissolved EPS from strain 34H, the same EPS but heat-treated, or dissolved EPS from the uninoculated growth medium. Results indicated that only the native (unheated) EPS of strain 34H was retained preferentially in the ice. Temperature and volumetric measurements of the ice further suggested a link between the heat-labile fraction of this EPS of marine bacterial origin and potential habitat alteration. Bacterial EPS may join algal EPS in our understanding of how extracellular polymers help to establish and sustain the microbial community that inhabits sea ice.

Production of cryoprotectant extracellular polysaccharide substances (EPS) by the marine psychrophilic bacteriumColwellia psychrerythraeastrain 34H under extreme conditionsThis article is one of a selection of papers in the Special Issue on Polar and Alpine Microbiology.

Extracellular polysaccharide substances (EPS) play critical roles in microbial ecology, including the colonization of extreme environments in the ocean, from sea ice to the deep sea. After first developing a sugar-free growth medium, we examined the relative effects of temperature, pressure, and salinity on EPS production (on a per cell basis) by the obligately marine and psychrophilic γ-proteobacterium, Colwellia psychrerythraea strain 34H. Over growth-permissive temperatures of ~10 to –4 °C, EPS production did not change, but from –8 to –14 °C when samples froze, EPS production rose dramatically. Similarly, at growth-permissive hydrostatic pressures of 1–200 atm (1 atm = 101.325 kPa) (at –1 and 8 °C), EPS production was unchanged, but at higher pressures of 400 and 600 atm EPS production rose markedly. In salinity tests at 10‰–100‰ (and –1 and 5 °C), EPS production increased at the freshest salinity tested. Extreme environmental conditions thus appear to stimulate EPS production by this strain. Furthermore, strain 34H recovered best from deep-freezing to –80 °C (not found for Earthly environments) if first supplemented with a preparation of its own EPS, rather than other cryoprotectants like glycerol, suggesting EPS production as both a survival strategy and source of compounds with potentially novel properties for biotechnological and other applications.