A rapid method for determining the antimicrobial activity of novel natural molecules

Heat-cured poly(methyl methacrylate) resin incorporated with different food preservatives as an anti-microbial denture base material

BACKGROUND/PURPOSE

The colonization of microorganisms onto denture bases is one common problem that can contribute to oral diseases. Herein, three food preservatives, including zinc oxide, potassium sorbate, and sodium metabisulfite were introduced as anti-microbial additives into a heat-polymerized poly(methyl methacrylate) (PMMA).

MATERIALS AND METHODS

Relative microbial reductions of the modified PMMA resins against Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans were evaluated. The in vitro cytotoxicity of the materials was measured against mouse fibroblast L929 cells. A three-point flexural test was performed to determine a flexural strength and modulus properties of the materials.

RESULTS

The incorporation of all preservative agents into the material diminished the microbial growth of three microbial species. The PMMA resin combined with sodium metabisulfite exhibited the greatest anti-microbial activity that reduced almost all bacterial cells and about 40% of C. albicans. All modified resins showed no significant cytotoxicity against L929 cells. The addition of food preservatives did not significantly alter the flexural strength of the PMMA resin (∼84-92 MPa). However, the flexural modulus of the PMMA incorporated with food preservatives (∼2,024-2,144 MPa) was significantly lower than the unmodified PMMA.

CONCLUSION

Three food preservatives, especially sodium metabisulfite, could be applied as anti-microbial additives into the denture base resin. The PMMA incorporated with the additives did not show cytotoxicity. Although, the addition of the food preservatives altered the mechanical properties, the materials still provided acceptable flexural properties.

Tetrazolium/Formazan Test as an Efficient Method to Determine Fungal Chitosan Antimicrobial Activity

Fungal chitosan was extracted from Aspergillus niger mycelia. The produced chitosan was characterized with deacetylation degree of 89.2%, a molecular weight of 2.4 × 104 Da, and 96.0% solubility in 1% acetic acid solution. The antibacterial activity of fungal chitosan was evaluated against two foodborne pathogens, that is, Salmonella typhimurium and Staphylococcus aureus, using the established antibacterial assays, for example, zone of growth inhibition and agar plat count tests, and using 2,3,5,-triphenyltetrazolium chloride (TTC) as chromogenic marker for qualitative and quantitative determining of antibacterial potentiality. The TTC (0.5% w/v) was added, at concentration of 10%, to cultured broth, containing chitosan with different concentrations then the formed formazan was separated. The formation of red formazan could be considered as a qualitative indication for antibacterial activity, whereas the measurement of color intensity for the resuspended red formazan, using spectrophotometer at 480 nm, provided a quantitative evidence for the strength of the used antibacterial agent. Regarding the rapidity, technical simplicity, and cost-effectiveness, TTC assay could be recommended as an efficient alternative method for qualitative and quantitative determination of chitosan antibacterial activity and could be suggested for general evaluation of antibacterial agents.

The effect of water extract of sumac (Rhus coriaria L.) and lactic acid on decontamination and shelf life of raw broiler wings

In an attempt to improve the bacteriological quality and refrigerated shelf life of broiler meat, 10-min surface wash treatments with sterile distilled water (DW), 8% (wt/vol) water extract of sumac (Rhus coriaria L.) fruits (WES), and 2% (vol/vol) lactic acid (LA) were compared by using a broiler wing model. The aerobic plate counts (log10 cfu/g) of psychrotrophs, mesophilic aerobes, Enterobacteriaceae, coliforms and presumptive fecal coliforms on the samples were determined. Immediately after a 10-min decontaminaton, the mean count of all the bacterial groups was determined to be 3.9, 2.6, and 1.7 (log10 cfu/g) for DW, WES, and LA, respectively. Because the postdecontamination population level of psychrotrophs, mesophiles, and Enterobacteriaceae were low in the LA-treated group compared to the WES group, an equity between the 2 groups in the point of view of the 3 bacterial groups existed at d 10 of cold storage (3 +/- 1 degrees C). Shelf life was 7 and 14 d for wings treated with DW and WES, respectively, whereas the LA-treated wings did not spoil after 14 d of cold storage (3 +/- 1 degrees C). Nevertheless, an undesirable pale color and an acidulous odor occurred in the LA-treated wings. In contrast, a good color appeared on the WES-treated wings, which was also superior to the color of the DW-treated wings. Such advantages of WES may be important for poultry processors and for consumers. However, the immediate decontamination and refrigerated shelf life extension potential of WES should be intensively studied in antimicrobial interventions in poultry processing plants.