Survival and Heat Resistance of Listeria monocytogenes after Exposure to Alkali and Chlorine

A strain of Listeria monocytogenes isolated from a drain in a food-processing plant was demonstrated, by determination of D values, to be more resistant to the lethal effect of heat at 56 or 59°C following incubation for 45 min in tryptose phosphate broth (TPB) at pH 12.0 than to that of incubation for the same time in TPB at pH 7.3. Cells survived for at least 6 days when they were suspended in TPB at pHs 9.0, 10.0, and 11.0 and stored at 4 or 21°C. Cells of L. monocytogenes incubated at 37°C for 45 min and then stored for 48 or 144 h in TPB at pH 10.0 were more resistant to heat treatment at 56°C than were cells stored in TPB at pH 7.3. The alkaline-stress response in L. monocytogenes may induce resistance to otherwise lethal thermal-processing conditions. Treatment of cells in 0.05 M potassium phosphate buffer (pH 7.00 ± 0.05) containing 2.0 or 2.4 mg of free chlorine per liter reduced populations by as much as 1.3 log(10) CFU/ml, while treatment with 6.0 mg of free chlorine per liter reduced populations by as much as 4.02 log(10) CFU/ml. Remaining subpopulations of chlorine-treated cells exhibited some injury, and cells treated with chlorine for 10 min were more sensitive to heating at 56°C than cells treated for 5 min. Contamination of foods by L. monocytogenes cells that have survived exposure to processing environments ineffectively cleaned or sanitized with alkaline detergents or disinfectants may have more severe implications than previously recognized. Alkaline-pH-induced cross-protection of L. monocytogenes against heat has the potential to enhance survival in minimally processed as well as in heat-and-serve foods and in foods on holding tables, in food service facilities, and in the home. Cells surviving exposure to chlorine, in contrast, are more sensitive to heat; thus, the effectiveness of thermal processing in achieving desired log(10)-unit reductions is not compromised in these cells

Participatory action research for enironmental health: Encountering Feire in the urban barrio

The community-based approach to health research and intervention is a model of inquiry rooted in Freire's participatory action research (PAR). We need to show, in concept and practice, what it is about PAR that may be well suited for the types of health issues we encounter in inner-city environments. What type of learning results, how does this respond to particular health issues in the urban context, and what are the particular challenges faced in translating Freire's model into today's urban setting?To investigate these questions, we describe a recent PAR project in Southeast Los Angeles, California - an area known to some as "Asthmatown." One salient finding of the research is that PAR allows the integration of complex and multiple forms of knowledge, and this is a necessary response to the complex and multiplex nature of cumulative impacts. There are challenges to translating the model to the urban setting, however, such as the difficulties of participation in today's urban milieu. The research leads to some lessons for practitioners, such as the need to build "constant" elements into PAR projects. Lastly, we reflect on implications of this model for institutional reform. © 2007 Urban Affairs Association.link_to_subscribed_fulltex