Antimicrobial action of selected plant-derived compounds against Listeria monocytogenes

Listeria monocytogenes causes listeriosis, a disease that can be fatal to immunocompromised individuals. Due to the number of outbreaks, recalls, and deaths linked to the consumption of contaminated ready-to-eat (RTE) foods, the United States government issued a directive for the control of L. monocytogenes in the production of RTE meats including the use of a post-lethality treatment and/or the addition of a growth inhibitor. Several methods to inhibit pathogenic bacteria in RTE foods are currently utilized. One method actively being studied involves the use of natural plant products as food antimicrobials. The present study evaluated the effectiveness of plant-derived compounds in controlling the growth of L. monocytogenes . Four antimicrobials (cranberry-CB, grape seed-GS, oregano-OR, and green tea-GT) were evaluated in culture media and two (CB and GS in combination with sodium lauryl sulfate-SLS) as dips for frankfurters (formulated with or without sodium lactate-SL). In culture media, GS had the highest inhibitory activity at both storage temperatures (4 and 10°C) and at all concentrations tested. In frankfurters without SL, 4 and 6 log reductions in the initial numbers of the pathogen were obtained with CB (+SLS) and GS (+SLS), respectively, and growth of survivors was inhibited up to day 14. In frankfurters with SL, a similar bacteriocidal effect was obtained with both CB (+SLS) and GS (+SLS) but growth of survivors was prevented for 90 days. The survival of acid adapted L. monocytogenes in culture media containing CB and GS was also assessed. Acid adapted cells were less affected by CB than the non-acid adapted at weeks 1 and 2; no differences in sensitivity to GS was observed between acid adapted and non-acid adapted cells. Lastly, preliminary evidence on the mode of action of GS on L. monocytogenes cells using transmission electron microscopy indicated possible damage to the cytoplasmic membrane

Antimicrobial action of selected plant-derived compounds against Listeria monocytogenes

Listeria monocytogenes causes listeriosis, a disease that can be fatal to immunocompromised individuals. Due to the number of outbreaks, recalls, and deaths linked to the consumption of contaminated ready-to-eat (RTE) foods, the United States government issued a directive for the control of L. monocytogenes in the production of RTE meats including the use of a post-lethality treatment and/or the addition of a growth inhibitor. Several methods to inhibit pathogenic bacteria in RTE foods are currently utilized. One method actively being studied involves the use of natural plant products as food antimicrobials. The present study evaluated the effectiveness of plant-derived compounds in controlling the growth of L. monocytogenes . Four antimicrobials (cranberry-CB, grape seed-GS, oregano-OR, and green tea-GT) were evaluated in culture media and two (CB and GS in combination with sodium lauryl sulfate-SLS) as dips for frankfurters (formulated with or without sodium lactate-SL). In culture media, GS had the highest inhibitory activity at both storage temperatures (4 and 10°C) and at all concentrations tested. In frankfurters without SL, 4 and 6 log reductions in the initial numbers of the pathogen were obtained with CB (+SLS) and GS (+SLS), respectively, and growth of survivors was inhibited up to day 14. In frankfurters with SL, a similar bacteriocidal effect was obtained with both CB (+SLS) and GS (+SLS) but growth of survivors was prevented for 90 days. The survival of acid adapted L. monocytogenes in culture media containing CB and GS was also assessed. Acid adapted cells were less affected by CB than the non-acid adapted at weeks 1 and 2; no differences in sensitivity to GS was observed between acid adapted and non-acid adapted cells. Lastly, preliminary evidence on the mode of action of GS on L. monocytogenes cells using transmission electron microscopy indicated possible damage to the cytoplasmic membrane.</p

Inhibition of Aminoglycoside 6′-N-Acetyltransferase Type Ib-Mediated Amikacin Resistance by Antisense Oligodeoxynucleotides

Amikacin has been very useful in the treatment of infections caused by multiresistant bacteria because it is refractory to the actions of most modifying enzymes. However, the spread of AAC(6′)-I-type acetyltransferases, enzymes capable of catalyzing inactivation of amikacin, has rendered this antibiotic all but useless in some parts of the world. The aminoglycoside 6′-N-acetyltransferase type Ib, which is coded for by the aac(6′)-Ib gene, mediates resistance to amikacin and other aminoglycosides. RNase H mapping and computer prediction of the secondary structure led to the identification of five regions accessible for interaction with antisense oligodeoxynucleotides in the aac(6′)-Ib mRNA. Oligodeoxynucleotides targeting these regions could bind to native mRNA with different efficiencies and mediated RNase H digestion. Selected oligodeoxynucleotides inhibited AAC(6′)-Ib synthesis in cell-free coupled transcription-translation assays. After their introduction into an Escherichia coli strain harboring aac(6′)-Ib by electroporation, some of these oligodeoxynucleotides decreased the level of resistance to amikacin. Our results indicate that use of antisense compounds could be a viable strategy to preserve the efficacies of existing antibiotics to which bacteria are becoming increasingly resistant

Antilisterial effects of gravinol-s grape seed extract at low levels in aqueous media and its potential application as a produce wash.

Grape seed extract (GSE) is a rich source of proanthocyanidins, a class of natural antioxidants reported to have wide-ranging bioactivity as anti-inflammatory, anticarcinogenic, and antimicrobial agents. The ability of GSE to rapidly inactivate Listeria monocytogenes in vitro and the generally recognized as safe status of GSE make this extract an attractive candidate for control of Listeria in or on foods. Previously, GSE has been used at relatively high concentrations (1%) in complex food matrices and in combination with other antimicrobials. We sought to characterize the antilisterial effects of a commercial GSE preparation (Gravinol-S) alone at much lower concentrations (0.00015 to 0.125%) in aqueous solution and to test its possible use as an antimicrobial wash for fresh produce surfaces. Based on broth microdilution tests, the MICs of GSE against L. monocytogenes Scott A and Listeria innocua ATCC 33090 were as low as 50 and 78 mg ml21, respectively. GSE was evaluated in 0.85% saline against live cells of L. innocua via flow cytometry, using propidium iodide as a probe for membrane integrity. At sub-MICs and after only 2 min of exposure, treatment with GSE caused rapid permeabilization and clumping of L. innocua, results that we confirmed for L. monocytogenes using fluorescence microscopy and Live/Dead staining. At higher concentrations (0.125%), GSE reduced viable cell counts for L. monocytogenes by approximately 2 log units within 2 min on tomato surfaces. These results suggest the potential for GSE as a natural control of Listeria spp. on low-complexity foods such as tomatoes.This article is from Journal of Food Protection 73(2): 266-273. Posted with permission.</p