Inhibitory relationships of resident bacteria isolated from the mantle fluids of Crassostrea virginica.

Thirteen aerobic, halotolerant marine bacterial strains were isolated from the mantle fluids and associated mucus of the eastern oyster Crassostrea virginica harvested from the highly impacted Black Rock Harbor in western Long Island Sound. All isolated strains were Gram negative and had previously been identified using 16S RNA gene sequence analysis. These 13 strains were examined for their ability to inhibit the growth of each other employing a diffusion agar method used by antibiotic assays. All challenger strains were able to inhibit at least one of the indicator isolates. Enhanced antimicrobial activity was observed from cultures of Pseudoalteromonas sp. (L), Shewanella sp. (H), Thalassospira sp. (JA), and Alteromonas sp. (JB) when used to challenge the indicator isolates. The indicator isolate most sensitive to antimicrobial activity was another Pseudoalteromonas species (KC) whose growth was inhibited by 10 of the challenger strains, whereas Pseudoalteromonas (L) was resistant to all growth challenges. Growth autoinhibition was observed with isolates Tenacibaculum ascidiaceicola (KC), Vibrio (B), and Shewanella (H) during a 24 h incubation. No antimicrobial growth inhibition was detected when 24 and 48 h cell-free extracts of these isolates were used to challenge indicator isolate growth.

The effects of tea polyphenols on Candida albicans: inhibition of biofilm formation and proteasome inactivation.

The adherence of Candida albicans to one another and to various host and biomaterial surfaces is an important prerequisite for the colonization and pathogenesis of this organism. Cells in established biofilms exhibit different phenotypic traits and are inordinately resistant to antimicrobial agents. Recent studies have shown that black and green tea polyphenols exhibit both antimicrobial and strong cancer-preventive properties. Experiments were conducted to determine the effects of these polyphenols on C. albicans. Standard growth curves demonstrated a 40% reduction in the growth rate constant (K) with a 2 mg/mL concentration of Polyphenon 60, a green tea extract containing a mixture of polyphenolic compounds. Cultures treated with 1.0 micromol/L -(-)epigallocatechin-3-gallate (EGCG), the most abundant polyphenol, displayed a 75% reduction of viable cells during biofilm formation. Established biofilms treated with EGCG were also reduced, by 80%, as determined through XTT (2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide) colorimetric assays. Identical concentrations of epigallocatechin and epicatechin-3-gallate demonstrated similar biofilm inhibition. Further investigations regarding the possible mechanism of polyphenol action indicate that in vivo proteasome activity was significantly decreased when catechin-treated yeast cells were incubated with a fluorogenic peptide substrate that measured proteasomal chymotrypsin-like and peptidyl-glutamyl peptide-hydrolyzing activities. Impairment of proteasomal activity by tea polyphenols contributes to cellular metabolic and structural disruptions that expedite the inhibition of biofilm formation and maintenance by C. albicans.

The effect of farnesol on amino acid incorporation by a wild-type and cell-wall variant strain of Candida albicans.

Farnesol, a quorum sensing (QS) signal, is produced by Candida albicans during high density growth and has been found to inhibit morphogenesis. This QS auto-inducing signal was discovered to increase amino acid incorporation by C. albicans when concentrations of farnesol increased to 10 microg/mL in yeast nitrogen broth. Farnesol concentrations greater than 10 microg/mL abolished the enhanced incorporation, and the magnitude of the increased incorporation was dependent on cell-surface hydrophobicity.