Growth and survival of exponential and stationary phase Salmonella during sausage fermentation

When raw meat is contaminated with enteropathogens, the growth state may appear in a mixture of phases. Survival for exponential and stationary phase cells differs, with stationary phase cells being generally more resistant. Our aim of this study was to investigate the survival of exponential and stationary phase Salmonella during freezing and to follow the survival/growth of these cells during subsequent sausage fermentation. Minced meat was inoculated with exponential and stationary phase Salmonella Thyphimurium, respectively, and frozen at -20ºC for up to 35 days. The meat was thawed overnight at 5ºC prior to sausage production

Acid stress response and protein induction in Campylobacter jejuni isolates with different acid tolerance.

<p>Abstract</p> <p>Background</p> <p>During the transmission route from poultry to the human host, the major foodborne pathogen <it>C. jejuni</it> may experience many types of stresses, including low pH caused by different acids. However, not all strains are equally sensitive to the stresses. The aim of this study was to investigate the response to acid stress of three sequenced <it>C. jejuni</it> strains with different acid tolerances using HCl and acetic acid.</p> <p>Results</p> <p>Two-dimensional gel electrophoresis was used for proteomic analysis and proteins were radioactively labelled with methionine to identify proteins only related to acid exposure. To allow added radioactive methionine to be incorporated into induced proteins, a modified chemically defined broth was developed with the minimal amount of methionine necessary for satisfactory growth of all strains. Protein spots were analyzed using image software and identification was done with MALDI-TOF-TOF. The most acid-sensitive isolate was <it>C. jejuni</it> 327, followed by NCTC 11168 and isolate 305 as the most tolerant. Overall, induction of five proteins was observed within the pI range investigated: 19 kDa periplasmic protein (p19), thioredoxin-disulfide (TrxB), a hypothetical protein Cj0706 (Cj0706), molybdenum cofactor biosynthesis protein (MogA), and bacterioferritin (Dps). Strain and acid type dependent differences in the level of response were observed. For strain NCTC 11168, the induced proteins and the regulator <it>fur</it> were analysed at the transcriptomic level using qRT-PCR. In this transcriptomic analysis, only up-regulation of <it>trxB</it> and <it>p19</it> was observed.</p> <p>Conclusions</p> <p>A defined medium that supports the growth of a range of <it>Campylobacter</it> strains and suitable for proteomic analysis was developed. Mainly proteins normally involved in iron control and oxidative stress defence were induced during acid stress of <it>C. jejuni</it>. Both strain and acid type affected sensitivity and response.</p

Quantifying the effect of natural microflora on growth of salmonellae in fresh pork

This study was undertaken to provide predictive models to help prevent health problems in relation to salmonellae in fresh pork. The models consider different time and temperature of storage as well as microbial interaction with the natural microflora in the meat. At six temperatures between 4 and 20°C, duplicate growth curves of Salmonella Typhimurium DT104 and Salmonella Derby were established in both sterile (irradiated) minced pork as well as in minced pork with a natural microflora