Listeria monocytogenes response to oxidative stress by sublethal sodium hypochlorite was investigated in this study. Continuous exposure of sublethal chlorine influenced biofilm formation and stress adaptation (homologous and heterologous) in L. monocytogenes. The biofilm forming ability of oxidative stress adapted and control cells were investigated on polystyrene surface at 22°C and 37°C. The oxidative stress adapted cells were found to form less biofilm in the presence of chlorine (p < 0.10) when compared to non-treated control cells at both the temperatures. In addition, the biofilm forming ability of L. monocytogenes was reduced significantly at higher sublethal chlorine concentrations (p < 0.10). In conclusion, oxidative stress adapted L. monocytogenes has developed tolerance to chlorine and some of the antibiotics. However, oxidative stress those cells did demonstrate an antibiofilm effect. This demonstrates that oxidative stress reduces L. monocytogenes biofilm formation but can also increase antibiotic resistance.

The objective of this study was to evaluate the efficacy of buffered vinegar in a marinade solution on inhibiting Listeria monocytogenes growth on cooked broiler breast meat. Broiler breasts were vacuum-tumbled for 30 min in a marinade consisting of dry (0%, 0.4% DV, 0.6%DV, and 0.8%) or liquid vinegar (1.5%), sodium chloride, sodium tripolyphospate, and water. The chicken breasts were then cooked to an internal temperature of 75°C. The breast meat was inoculated with L. monocytogenes, placed into modified atmosphere packaging, and stored at 2°C plus/minus 2 for 0-60 days. L. monocytogenes growth was stable on treatments for up to 30 days. However, from 35 to 60 days, the buffered vinegar treatments had fewer L. monocytogenes counts (P<0.05) than the control treatment. In addition, the 0.8 % DV and 1.5 % LV treatments had fewer than 2.0 log counts of L. monocytogenes after 60 days of storage.

Listeria monocytogenes is a food-borne pathogen responsible for the disease listeriosis. The infectious process depends upon survival in high bile salt conditions encountered throughout the gastrointestinal tract, including the gallbladder. However, it is not clear how bile salt resistance mechanisms are induced, especially under physiologically relevant conditions. This study sought to determine how L. monocytogenes responds to bile salts under anaerobic conditions. The study found resistance to be strain specific and not dependent upon virulence. Changes in the expressed proteome were analyzed using multidimensional protein identification technology coupled with electrospray ionization tandem mass spectrometry. A general response among virulent and avirulent strains found significant alterations in intensity of cell wall associated proteins, DNA repair proteins, protein folding chaperones and oxidative response proteins. Strain viability was correlated with an initial osmotic stress response followed by strain specific proteins associated with biofilm formation in EGDe and a transmembrane efflux pump in F2365.

The rates of the US hospitalization and mortality caused by Listeria monocytogenes was estimated to be the highest of 31 food-borne pathogens including Salmonella, Escherichia coli, Campylobacter, and Clostridium. This pathogen has an ability to survive under extreme conditions widely found in the natural environment and food. Among 13 serovars L. monocytogenes serovar 4b, 1/2a and 1/2b are mainly associated with human listeriosis outbreaks. The deadliest outbreaks of human listeriosis and massive product recalls in multi-states were associated with ready-to-eat (RTE) food products such as mexican-style cheese, turkey deli meat, cabbage, and cantaloupes contaminated with the bacterium. Thus, contamination of food products with L. monocytogenes is a major concern for the food industry, regulatory agents and consumers. This study used oligonucleotide probe-based DNA array, quantitative real time RT-PCR, gene manipulation, biochemical assays, and electron microscopy techniques to better understand the molecular mechanisms of L. monocytogenes under stress conditions on various food matrices,. The transcriptome profiles of L. monocytogenes via microarray analysis and quantitative PCR identified genes that are involved in adaptation, attachment, or survival and growth of the pathogen under a stress condition on a food matrix. The mechanistic and functional studies further characterized the biological properties of L. monocytogenes in various RTE food products. We showed that specific genes involved in energy metabolism, biosynthesis of proteins, and cellular processes to affect listerial growth or adaptation to a RTE meat matrix were changed with no associated changes in virulence factor expression. We also reported that the effects of salt stress on the expression of genes involved in PTS and its related metabolic enzymes in L. monocytogenes. In addition, a novel gene involved in attachment to RTE vegetables and fruits was discovered. The concern about the prevalence of L. monocytogenes in RTE food has been escalated by recent food-borne outbreaks, suggesting that the prevention of human listeriosis become the top priority for the food industry. Data from these studies help us to better understand the survival, growth and contamination of the bacterium under different conditions. The information will help the development of prevention strategies in RTE meat products, vegetables and fruits.

The purpose of this study was to induce an oxidative-stress adaptation in Listeria monocytogenes Bug600 (serotype 1/2a) and F1057 (serotype 4b) by pre-exposing to sublethal H2O2 and alkali-stress either singly or sequentially. Our findings show that the sequential pre-exposure of cells to pH 9 for 30 min treatment followed by 50 ppm H2O2 for 30 min at 37°C yielded the highest oxidative-stress resistant phenotypes of L. monocytogenes Bug600 and F1057. The sublethal H2O2 and sublethal alkali-stress induced oxidative-stress adaptations were completely reversible within 60 min at 37°C in the absence of such sublethal stress. However, the oxidative-stress adaptation induced at 37°C was stable at 4°C over a 24 h test period in both L. monocytogenes Bug600 and F1057. Future studies will focus on the potential cross-resistance of oxidative-stress adapted L. monocytogenes serotypes 1/2a and 4b to commonly used disinfectants and GRAS antimicrobials.

The purpose of this study is to determine the effect of temperature on inducing an alkaline-tolerance response in L. monocytogenes (Lm) serotypes 1/2a and 4b. When Lm cells were pre-exposed to a sublethal alkali pH of 9.0 at different temperatures, two main patterns were observed: (1) Alkali-stress adaptation was readily induced in Lm when cells were pre-exposed to a sublethal alkali pH of 9.0 for 5-15 min at 37°C or 22°C; and (2) Alkali-stress adaptation was not induced in Lm when cells were pre-exposed to a sublethal alkali pH of 9.0 for 1 h at 4°C. However, exposure of Lm to 4°C for 24 h enhanced its survival against lethal alkaline challenge (pH 11.5). Also, alkali-stress adaptation if occurred at 37°C or 22°C was highly stable at 4ºC even in the absence of mild alkaline stress which should be taken into account while conducting risk analysis for this pathogen.

No description available.

Stormwater runoff is a major environmental concern, particularly in urban environments. Trends in managing stormwater have evolved (and continue to evolve) from a quantity only approach into a sustainable approach, which integrates quantity, quality, the environment, and aesthetics. Best management practices (BMPs) and Low Impact Development (LID) are two well-documented techniques capable of managing to sustainable standards. There are a number of stormwater models available to design professionals today. However, there are few which integrate site-scale BMP/LID analysis in a simplified fashion. The purpose of this study is to determine if there is a demand in the design profession for simplified stormwater modeling tools to help designers make informed decisions about integrating BMP/LID strategies into site plans. A Web-based questionnaire was administered to a group of design professionals to determine their knowledge of BMPs and their technological needs and preferences in meeting stormwater goals and requirements.

Listeria monocytogenes is a deadly, Gram-positive foodborne pathogen that is ubiquitous in the environment. The bacterium expresses a number of virulence and stress adaptation proteins that support its pathogenic capabilities. Two-dimensional gel electrophoresis (2-DE) was used to map L. monocytogenes surface proteins, which play a central role in virulence, and to examine protein expression by L. monocytogenes grown on ready-to-eat meat, an important source of Listeria infections. A novel method for solubilization of surface proteins from L. monocytogenes for 2-DE was developed. Additionally, the unique proteome expressed by L. monocytogenes grown on a meat matrix was uncovered. The developed solubilization method will facilitate efforts to identify and routinely compare surface proteins of Listeria by 2-DE. Furthermore, the 2-DE database of proteins expressed by L. monocytogenes grown on a meat matrix will allow further understanding of the interactions of Listeria with its food environment that influence its ability to cause disease.

Post process application of antimicrobials is one method to control recontamination of Listeria monocytogenes on cooked RTE meat products. This study evaluated the antilisterial effect of externally applied solutions of nisin, buffered solution of sodium citrate supplemented with sodium diacetate (SCSD) and a combined solution of the two antimicrobials on commercial beef frankfurters formulated without antimicrobials. Autoclaved frankfurters were inoculated (104 -105 CFU/g), dipped (5 min, 25 ± 2°C) in treatments consisting of 2000; 4000;or 6000 IU/ml nisin, and buffered solutions of 2.5; 3.0; or 3.5% SCSD (Study I), and 6000 IU/ml nisin followed by 3.5% SCSD, or 3.5% SCSD followed by 6000 IU/ml nisin, or a combined solution containing both 6000 IU/ml nisin and 3.5% SCSD(Study II). Treated hot dogs were vacuum packaged and stored at 4 and 10°C. L. monocytogenes counts were determined on Modified Oxford Agar on 0, 14, 28, and 42 days at 4°C and 0, 4, 8, 12, 16, and 20 days at 10°C. Nisin (6000 IU/ml) initially reduced L. monocytogenes population by 2.1 and 2.5 logs (at 4 and 10°C, respectively on day 0), buffered SCSD (3.5%) by 1.1 and 0.2 logs (at 4 and 10°C, respectively on day 0) and the combined solution by 1.7 and 2.0 logs (at 4 and 10°C, respectively on day 0). The combined solution was the most effective treatment compared to nisin and buffered SCSD, used in sequence or alone, since it inhibited the growth of L. monocytogenes during 28 days at 4°C. The buffered SCSD was effective against L. monocytogenes at 4°C but not at 10°C. Further research is needed to investigate the effectiveness of buffered SCSD with other antimicrobials. The results of this study may be useful for further research on combinations of antimicrobials.