Growths kinetics comparison of clinical and seafood Listeria monocytogenes isolates in acid and osmotic environment.

Comparison of pathogenic bacterial strains of clinical origin with strains of the same species isolated from the environment may be a valuable tool for microbial risk assessment, especially for foodborne pathogens. Thus, a number of Listeria monocytogenes strains responsible for human cases of listeriosis, in relation to the consumption of contaminated seafood, have been compared with "natural" L. monocytogenes strains isolated from similar seafood products. Complete factorial designs were used to assess quantitatively the growth abilities of four clinical and four seafood isolates of L. monocytogenes placed in various environmental conditions. The cells were submitted to acid and osmotic stress as they were in stationary phase (constant condition) or in exponential phase (dynamic condition). The effects and interactions of pH (5-7) and NaCl concentration (0.5-8% v/v) were studied at two growth temperatures (10 and 20 degrees C). Growth parameters (lag and generation times calculated with Gompertz equation) were used to compare the behavior of the strains with respect to the conditions of culture. The results indicated an overall weak effect of acid stress alone, whereas osmotic stress clearly affected bacterial growth and a synergic effect between these two factors was observed. Clinical strains displayed better adaptation than seafood strains in stationary phase, however, this difference was not verified in exponential phase. Low temperature (10 degrees C) usually confirmed the observations at 20 degrees C, and the differences between clinical and food strains were more pronounced. Finally, a classification of the eight strains, based on the collected data, showed three groups: (i) seafood strains, (ii) three clinical strains and (iii) the last clinical strain, alone due to its high resistance to adverse conditions.

Molecular epidemiology of Listeria monocytogenes isolates collected from the environment, raw meat and raw products in two poultry- and pork-processing plants.

AIMS: In order to study the transmission of Listeria monocytogenes in a poultry and a pork meat plant, we analysed the contamination by this pathogen over several months. METHODS AND RESULTS: Five hundred and two isolates of L. monocytogenes were collected and characterized by genotyping and serotyping. Thirty-seven genotypes were obtained by ApaI-restriction analysis-pulsed field gel electrophoresis (REA-PFGE) and 35 by SmaI-REA-PFGE and resulted in 50 combined genotypes. The tracing of the contamination in both plants showed that some clones were able to survive for several months. However, some other clones were found only during processing operations, were not detectable after cleaning and seemed to enter continuously into the plant. CONCLUSIONS: Some L. monocytogenes strains may persist for a long period in the plant environment. Different genotypes can be associated with poultry as well as pork meat. SIGNIFICANCE AND IMPACT OF THE STUDY: Listeria monocytogenes contamination can be due to contaminated raw materials, bacterial spread and also ineffective cleaning procedures.