The antimicrobial properties of the American cranberry were studied against Escherichia coli O157:H7, Listeria monocytogenes, and Lactobacillus rhamnosus to determine the effects on growth inhibition, membrane permeability, and injury. Cranberry powder was separated using a C-18 Sep-Pak cartridge into sugars plus organic acids (F1), monomeric phenolics (F2), and anthocyanins plus proanthocyanidins (F3). Fraction 3 was further separated into anthocyanins (F4) and proanthocyanidins (F5) using an LH-20 Sephadex column. Each fraction was diluted in the brain heart infusion (BHI) broth to determine the minimum inhibitory/bactericidal concentrations (MIC/MBC). L. monocytogenes was the most susceptible to cranberry fraction treatment with the lowest MIC/MBC for each treatment, followed by E. coli O157:H7 and L. rhamnosus. Membrane permeability and potential was studied using LIVE/DEAD viability assay and using Bis (1, 3-dibutylbarbituric acid) trimethine oxonol (DiBAC4), respectively. L. rhamnosus demonstrated the highest permeability followed by E. coli O157:H7, and L. monocytogenes. L. rhamnosus demonstrated the highest recovery followed by E. coli O157:H7, and L. monocytogenes. Each cranberry fraction demonstrated membrane hyperpolarization at their native pH, while F2, F3, and F5 demonstrated membrane depolarization at neutral pH. With this knowledge cranberry compounds may be used to prevent maladies and potentially substitute for synthetic preservatives and antibiotics.
We developed a rapid and reliable technique for simultaneous detection of Salmonella Typhimurium, Escherichia coli O157:H7 and Listeria monocytogenes that can be used in food products. Magnetic nano-beads (MNBs) based immunomagnetic separation (IMS) was used to separate the target bacterial cells while multiplex PCR (mPCR) was used to amplify the target genes. To detect only the viable bacteria, propidium monoazide (PMA) was applied to selectively suppress the DNA detection from dead cells. The results showed the detection limit of IMS-PMA-mPCR assay was about 102 CFU/ml (1.2 × 102 CFU/ml for S. Typhimurium, 4.0 × 102 CFU/ml for E. coli O157:H7 and 5.4 × 102 CFU/ml for L. monocytogenes) in pure culture and 103 CFU/g (5.1 × 103 CFU/g for S. Typhimurium, 7.5 × 103 CFU/g for E. coli O157:H7 and 8.4 × 103 CFU/g for L. monocytogenes) in spiking food products samples (lettuce, tomato and ground beef). This report has demonstrated for the first time, the effective use of rapid and reliable IMS combined with PMA treatment and mPCR assay for simultaneous detection of viable S. Typhimurium, E. coli O157:H7 and L. monocytogenes in spiked food samples. It is anticipated that the present approach will be applicable to simultaneous detection of the three target microorganisms for practical use.
FoodWorld 