The particular behaviour of Listeria monocytogenes under sub-optimal conditions.

Listeria monocytogenes is a ubiquitous pathogenic microorganism which has been described as growing at temperatures of interest to food production and especially at low temperatures (-2 degrees to 8 degrees C) in storage process. However, the general relationship between the maximum specific growth rate, mumax and temperature has not often been studied for L. monocytogenes in the whole temperature range from minimal to maximal growth temperature. A global analysis of this relationship for temperatures between -2 degrees C and 42 degrees C was therefore done. The global shape of this relationship was that usually observed for microorganisms, especially in the neighbourhood of the optimal temperature, Topt. But a more detailed study showed the existence of a so-called "change temperature", occurring between 10 degrees and 15 degrees C, below which L. monocytogenes grows faster than one would expect. This implies that the minimal growth temperature of both studied strains of L. monocytogenes is lower than expected.

Differential growth of Listeria monocytogenes at 4 and 8°C: Consequences for the Shelf Life of Chilled Products.

Growth rates and lag times of Listeria monocytogenes at 4 and 8°C were compared in dairy products (milk, cream, and cheese), minced beef, and smoked salmon. Results showed that an increase in incubation temperature from 4 to 8°C leads to a significant decrease in time required to reach a given bacterial population density. The decreases were about 50% on cheese surfaces, 60 to 65% in milk and cream, and 75 to 80% in minced beef and smoked salmon. Consequences on the shelf life of chilled products are discussed on the basis of a simple and general linear relationship between the relative decrease in shelf life and generation time. This relationship was experimentally highlighted and theoretically demonstrated.

Epitopic regions for antibodies against tumor necrosis factor alpha. Analysis by synthetic peptide mapping.

The location of biologically relevant epitopes on human tumor necrosis factor alpha (hTNF-alpha) was evaluated by testing the immunoreactivity of anti-TNF-alpha antibodies against 149 sequential, overlapping octamer peptides. A goat polyclonal antibody raised against recombinant hTNF-alpha, which neutralizes hTNF-alpha biological activities, reacted with oligopeptides corresponding to hTNF-alpha residues 7-11, 17-23, 30-39, 42-49, 106-112, and 135-142. A possible assembled epitopic region (residues 25, 27, and 144) for neutralizing murine monoclonal antibodies designated 11D7G4 and 9C4G5 was deduced from the fact that they bound to tripeptides, mimicking a discontinuous epitope. These antigenic regions wer found to include of adjoin poorly conserved amino acids and they were located in the turns between beta-sheets on the surface of the molecule. Three of the sequential epitopic regions and an assembled region were closely related to the receptor binding sites proposed in several other studies. These antibodies appear to neutralize TNF-alpha activities by directly masking receptor binding sites.

Convenient Model To Describe the Combined Effects of Temperature and pH on Microbial Growth.

A new model in which the maximum microbial specific growth rate ((mu)(infmax)) is described as a function of pH and temperature is presented. The seven parameters of this model are the three cardinal pH parameters (the pH below which no growth occurs, the pH above which no growth occurs, and the pH at which the (mu)(infmax) is optimal), the three cardinal temperature parameters (the temperature below which no growth occurs, the temperature above which no growth occurs, and the temperature at which the (mu)(infmax) is optimal), and the specific growth rate at the optimum temperature and optimum pH. The model is a combination of the cardinal temperature model with inflection and the cardinal pH model (CPM). The CPM was compared with the models of Wijtzes et al. and Zwietering et al. by using previously published data sets. The models were compared on the basis of the usual criteria (simplicity, biological significance and minimum number of parameters, applicability, quality of fit, minimum structural correlations, and ease of initial parameter estimation), and our results justified the choice of the CPM. Our combined model was constructed by using the hypothesis that the temperature and pH effects on the (mu)(infmax) are independent. An analysis of this new model with an Escherichia coli O157:H7 data set showed that there was a good correspondence between observed and calculated (mu)(infmax) values. The potential and convenience of the model are discussed.