Listeria

The distributions of the times to turbidity for wells inoculated with single cells of Listeria innocua were determined in different environmental conditions (pH 4.5 to 7 and with 0.5% to 8% of NaCl at 30 degrees C). It was established by statistical analysis that the main source of the variability of the detection times, T, is the variability of individual lag times. A linear relation dev(T) approximately T was observed between the detection times and their standard deviation. At slow growth, other sources of variability became increasingly significant.

When shredded or sliced carrots were inoculated with Listeria monocytogenes the number of viable listerias decreased rapidly. On carrot slices stored at 8 degrees C there was a decrease after 3d followed by an increase, after 7d, to numbers similar to those present initially. The numbers of spoilage micro-organisms increased throughout storage at 8 degrees C. Carrots macerated in a Stomacher Lab Blender also showed an antilisterial activity which resulted in a decrease in number of viable bacteria and in sublethal damage. The effect was shown by five carrot cultivars and acted on nine strains of L. monocytogenes and single strains of L. innocua, L. ivanovii, L. seeligeri, L. melshimeri. This antilisterial effect was heat-labile, was inactivated after a few hours at 4 degrees C or at 30 degrees C and was active over the pH range 5.8 to 7.0. Maceration of carrots in an Atomix blender for 1 min or in liquid nitrogen destroyed the antilisterial activity.

To ensure that the residents are kept as safe as possible from food poisoning and food-associated illness, by adopting the highest standards of food hygiene and food preparation. If food poisoning does occur, the organization will ensure that its staff is able to recognize the signs and symptoms do a full investigation and take corrective action.

A modification to Performance-Tested MethodSM (PTM) 070601, Reveal® Listeria Test (Reveal), is described. The modified method uses a new media formulation, LESS enrichment broth, in single-step enrichment protocols for both foods and environmental sponge and swab samples. Food samples are enriched for 2730 h at 30C and environmental samples for 2448 h at 30C. Implementation of these abbreviated enrichment procedures allows test results to be obtained on a next-day basis. In testing of 14 food types in internal comparative studies with inoculated samples, there was a statistically significant difference in performance between the Reveal and reference culture U.S. Food and Drug Administration's Bacteriological Analytical Manual (FDA/BAM) or U.S. Department of Agriculture-Food Safety and Inspection Service (USDA-FSIS) methods for only a single food in one trial (pasteurized crab meat) at the 27 h enrichment time point, with more positive results obtained with the FDA/BAM reference ...

The antilisterial efficiency of three bacteriocins from lactic acid bacteria, lactocin 705 (produced by L. casei CRL705, 17000 AU/ml), enterocin CRL35 (produced by E. faecium CRL35, 17000 AU/ml), and nisin (2000 IU/ml), was tested in broth, individually and in combination against Listeria monocytogenes and Listeria innocua. Both Listeria species showed an initial decrease in viable counts followed by the regrowth of the survivors after 1 h in the presence of each bacteriocin. A greater antilisterial effect was observed when the bacteriocins were combined in pairs, maximal inhibition being reached when nisin was involved. When a mix of the three bacteriocins was used, no survivors were observed after 24 h of incubation. Similar results were obtained when the bacteriocin combinations were tested in a meat system, indicating that the use of more than one LAB bacteriocin in combination may be effective in preventing the spontaneous emergence of a bacteriocin-resistant Listeria population.

A pathogen is defined as a bacterial, viral or other microbial agent that causes disease. It might therefore be a surprise that studies with a number of pathogens have, in recent years, yielded some of the most exciting new insights into the regulation of actin polymerization in the ...

The RapidChek Listeria NextDay test system is designed for the presumptive detection and identification of Listeria species in food in a minimum of 27 hours via a one-step system.  This study evaluated the performance of RapidChek Listeria NextDay against other commercially available rapid methods for the detection of Listeria spp. in food.  Samples of imitation crab were inoculated with 0, 1.25 or 12.5 CFU/sample Listeria monocytogenes, and cold stressed 72 hours prior to testing.  Samples were tested using the FDA Bacteriological Analytical Manual (BAM) method, method alpha - a 27 hour lateral flow method, method beta - a 48 hour automated immunoassay method, and method gamma - a 28 hour automated immunoassay.  Results were confirmed per FDA BAM guidelines on MOX agar plates.  Presumptive results from the rapid test methods were compared to results of the FDA BAM method, with statistical analysis performed for the fractional recovery spikes.  In the first test, RapidChek demonstrated a χ2 of 1.26, with 100% sensitivity and specificity; method alpha showed a χ2 of 2.08, 87% sensitivity and 100% specificity; method beta showed a χ2 of 0.61, 100% sensitivity and specificity.  In the second test run, RapidChek demonstrated a χ2 of 0.17, with 100% sensitivity and specificity, and method gamma showed a statistically significant χ2 of 4.18, 100% sensitivity and 67% specificity.  RapidChek Listeria NextDay performed equivalently to the FDA BAM method and a 48-hour automated method, and demonstrated greater accuracy than other following day result methods tested.

We aimed at evaluating the prevalence of Listeria species isolated from food samples and characterizing food and human cases isolates. Between 2005 and 2007, one hundred food samples collected in the markets of Tunis were analysed in our study. Five strains of Listeria monocytogenes responsible for human listeriosis isolated in hospital of Tunis were included. Multiplex PCR serogrouping and pulsed field gel electrophoresis (PFGE) applying the enzyme AscI and ApaI were used for the characterization of isolates of L. monocytogenes. We have developed a rapid microarray-based assay to a reliable discrimination of species within the Listeria genus. The prevalence of Listeria spp. in food samples was estimated at 14% by using classical biochemical identification. Two samples were assigned to L. monocytogenes and 12 to L. innocua. DNA microarray allowed unambiguous identification of Listeria species. Our results obtained by microarray-based assay were in accordance with the biochemical ide...

Batch culture of biofilms on peg lids is a versatile method that can be used for microtiter determinations of biofilm antimicrobial susceptibility. In this paper, we describe a core protocol and a set of parameters (surface composition, the rate of rocking or orbital motion, temperature, cultivation time, inoculum size, atmospheric gases and nutritional medium) that can be adjusted to grow single- or multispecies biofilms on peg surfaces. Mature biofilms formed on peg lids can then be fitted into microtiter plates containing test agents. After a suitable exposure time, biofilm cells are disrupted into a recovery medium using sonication. Microbicidal endpoints can be determined qualitatively using optical density measurements or quantitatively using viable cell counting. Once equipment is calibrated and growth conditions are at an optimum, the procedure requires approximately 5 h of work over 4-6 d. This efficient method allows antimicrobial agents and exposure conditions to be teste...

The antimicrobial activity against Listeria innocua of three different combined non-thermal treatments, along with the impact on color and texture on green bean samples, was evaluated. In this study a bioactive coating formulation based on modified chitosan containing 0.05% nanoemulsion of mandarin essential oil was tested in combination with γ-irradiation, UV-C and ozonated water treatments, and the results in terms of antimicrobial activity, color and texture changes, were evaluated during 14 days storage. The combined coating and γ-irradiation treatment gave promising results, showing 3.3 log CFU/g initial microbial reduction, and exhibiting a strong synergistic antimicrobial effect. The treatment based on UV-C and coating formulation allowed a 3 log CFU/g reduction of initial L. innocua population on samples, showing a good residual antimicrobial activity and preventing loss of firmness and color changes during storage. The combined treatment of coating and ozonated water did no...

Lactobacillus curvatus LTH 1174, a strain isolated from fermented sausage, produces the antilisterial bacteriocin curvacin A. Its biokinetics of cell growth and bacteriocin production as a function of temperature (20-38 degrees C) and pH (4.8-7.0) were investigated in vitro during laboratory fermentations using de Man, Rogosa and Sharpe (MRS) medium. A predictive, successfully validated model was set up to describe the influence of temperature and pH on the microbial behavior. Both cell growth and bacteriocin activity were influenced by changes in temperature and pH. The optimum temperature value for cell growth, 34.5 degrees C, did not correspond with the optimum temperature for curvacin A production (20-27 degrees C). Interestingly, the pH range for growth and curvacin A production was broad. Thus, Lb. curvatus LTH 1174 seems to be a promising bacteriocin-producing strain for use in European sausage fermentations that are performed at temperatures near 25 degrees C.

This study compares the feature of different media with the combination of selective with non-selective media in a TAL method for recovery of Listeria innocua cells exposed to thermal treatments. Experiments were conducted in broth at constant temperature (52.5 and 65.0 °C) and pH (4.5 and 7.5) conditions, using NaCl or glycerol to adjust water activity to 0.95. Four different media were used in bacterial cell enumeration: (i) a non-selective medium – TSAYE, (ii) two selective media – TSAYE + 5%NaCl and Palcam Agar and (iii) TAL medium (consisting of a layer of Palcam Agar overlaid with one of TSAYE).Two food products were used as case studies aiming at comparison of results obtained on selective and TAL media enumeration. Parsley samples were inoculated with L. innocua and subjected to posterior thermal treatments both under isothermal (52.5, 60.0 and 65.0 °C) and non-isothermal (heating rate of 1.8 °C/min from 20.0 to 65.0 °C) conditions. The recovery capability of TAL method was also studied when a pre-cooked frozen food (i.e. meat pockets) was fried (oil temperature of ∼180 °C). TAL method proved to be better than Palcam Agar in terms of capability to recover injured cells and was effective in L. innocua enumeration when non-sterile samples were analysed.

We investigated the degree of physiological damage to bacterial cells caused by optical trapping using a 1,064-nm laser. The physiological condition of the cells was determined by their ability to maintain a pH gradient across the cell wall; healthy cells are able to maintain a pH gradient over the cell wall, whereas compromised cells are less efficient, thus giving rise to a diminished pH gradient. The pH gradient was measured by fluorescence ratio imaging microscopy by incorporating a pH-sensitive fluorescent probe, green fluorescent protein or 5(6)-carboxyfluorescein diacetate succinimidyl ester, inside the bacterial cells. We used the gram-negative species Escherichia coli and three gram-positive species, Listeria monocytogenes, Listeria innocua, and Bacillus subtilis. All cells exhibited some degree of physiological damage, but optically trapped E. coli and L. innocua cells and a subpopulation of L. monocytogenes cells, all grown with shaking, showed only a small decrease in pH...