Rhamnus prinoides (gesho) stem extract prevents co-culture biofilm formation by Streptococcus mutans and Candida albicans.

Streptococcus mutans and Candida albicans exhibit a symbiotic relationship to form polymicrobial biofilms that exacerbate oral infections including early-childhood caries, periodontitis and candidiasis. Rhamnus prinoides (gesho) has traditionally been used for the treatment of a variety of illnesses and was recently found to inhibit Gram-positive bacterial biofilm formation. We hypothesized that Rhamnus prinoides extracts have anti-biofilm activity against S. mutans and C. albicans mono- and dual-species biofilms. Ethanol extracts were prepared from gesho stems and leaves; then anti-biofilm activity was assessed using crystal violet, resazurin and XTT staining. Ethanol extracts significantly inhibited Streptococcus mutans and Candida albicans mono-species biofilm formation up to 97 and 75%, respectively. The stem ethanol extract disrupted S. mutans and C. albicans co-culture synergism, with 98% less polymicrobial biofilm formation than the untreated control. Additionally, this extract inhibited planktonic S. mutans cell growth and decreased biofilm polysaccharide production up to 99%. The reduction in polysaccharide production is likely a contributing factor in the anti-biofilm activity of GSE. These findings indicate that gesho or gesho-derived compounds may have potential as additives to oral hygiene products. SIGNIFICANCE AND IMPACT OF THE STUDY: Oral Streptococcus mutans and Candida albicans biofilms are associated with a variety of illnesses. When occurring together, the resulting infections are especially challenging to treat due to enhanced biofilm formation and antibiotic resistance. More therapeutics that can effectively prevent polymicrobial biofilm formation and disrupt interspecies synergism are needed. Rhamnus prinoides ethanol extracts significantly inhibited dual-species biofilm formation and disrupted interspecies synergism.

Colorimetric method for identifying plant essential oil components that affect biofilm formation and structure.

The specific biofilm formation (SBF) assay, a technique based on crystal violet staining, was developed to locate plant essential oils and their components that affect biofilm formation. SBF analysis determined that cinnamon, cassia, and citronella oils differentially affected growth-normalized biofilm formation by Escherichia coli. Examination of the corresponding essential oil principal components by the SBF assay revealed that cinnamaldehyde decreased biofilm formation compared to biofilms grown in Luria-Bertani broth, eugenol did not result in a change, and citronellol increased the SBF. To evaluate these results, two microscopy-based assays were employed. First, confocal laser scanning microscopy (CLSM) was used to examine E. coli biofilms cultivated in flow cells, which were quantitatively analyzed by COMSTAT, an image analysis program. The overall trend for five parameters that characterize biofilm development corroborated the findings of the SBF assay. Second, the results of an assay measuring growth-normalized adhesion by direct microscopy concurred with the results of the SBF assay and CLSM imaging. Viability staining indicated that there was reduced toxicity of the essential oil components to cells in biofilms compared to the toxicity to planktonic cells but revealed morphological damage to E. coli after cinnamaldehyde exposure. Cinnamaldehyde also inhibited the swimming motility of E. coli. SBF analysis of three Pseudomonas species exposed to cinnamaldehyde, eugenol, or citronellol revealed diverse responses. The SBF assay could be useful as an initial step for finding plant essential oils and their components that affect biofilm formation and structure.

Plant compounds that induce polychlorinated biphenyl biodegradation by Arthrobacter sp. strain B1B.

Plant compounds that induced Arthrobacter sp. strain B1B to cometabolize polychlorinated biphenyls (PCBs) were identified by a screening assay based on the formation of a 4,4'-dichlorobiphenyl ring fission product. A chemical component of spearmint (Mentha spicata), l-carvone, induced Arthrobacter sp. strain B1B to cometabolize Aroclor 1242, resulting in significant degradation of 26 peaks in the mixture, including selected tetra- and pentachlorobiphenyls. Evidence for PCB biodegradation included peak disappearance, formation of a phenylhexdienoate ring fission product, and chlorobenzoate accumulation in the culture supernatant. Carvone was not utilized as a growth substrate and was toxic at concentrations of greater than 500 mg liter-1. Several compounds structurally related to l-carvone, including limonene, p-cymene, and isoprene, also induced cometabolism of PCBs by Arthrobacter sp. strain B1B. A structure-activity analysis showed that chemicals with an unsaturated p-menthane structural motif promoted the strongest cometabolism activity. These data suggest that certain plant-derived terpenoids may be useful for promoting enhanced rates of PCB biodegradation by soil bacteria.