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| Author(s): |
Vinicius Buccelli Ribeiro
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ) |
| Defense date: | 2012-12-13 |
| Examining board members: |
Maria Teresa Destro;
Bernadette Dora Gombossy de Melo Franco;
Marina Baquerizo Martinez;
Marcia Pinto Alves Mayer;
Patrícia Severino
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| Advisor: | Maria Teresa Destro |
| Abstract | |
The control of Listeria monocytogenes (Lm) in food processing plants is difficult due to its ability to form biofilms and adapt to adverse environmental conditions. The survival at high concentrations of sodium chloride and growing at low temperatures are two other important features of Lm isolates, including the two most prevalent serotypes (1/2a and 4b). The objectives of this study were to evaluate the growing behavior, global gene expression profile and virulence potential of the two main serotypes of Lm under osmotic stress environments encountered by these microorganisms in the food industry. 22 Lm strains - 12 isolated from clinical cases (six strains serotype 4b and six serotype 1/2a) and 10 isolated from food (six serotype 4b and four serotype 1/2a) - plus one L. monocytogenes Scott A and one Listeria innocua were inoculated into BHI broth with water activity (aw) 0.94 (11% NaCl) and were incubated at 4°C, 10°C and 25°C during 73, 42 and 15 days respectively. At 4°C, the majority of strains both clinical and food were able to remain viable and to grow (up to 2 log CFU/ml). At 10°C, most strains could grow but significant differences (p < 0.05) on the lag phase duration between the serotypes 1/2a and 4b strains, regardless their origin, were observed (lag1/2a > lag4b). Statistical differences were also observed related to Lm serotype 4b strains when grown in BHI with aw 0.94 at 25°C, that showed higher maximum growth rate and final density (p < 0.05) compared to Lm serotype 1/2a strains. Regarding the virulence potential, there were no statistical differences among serotypes with respect to its hemolytic activity, however, the invasiveness of serotype 4b strains in Caco-2 cells was higher (p <0.05) than serotype 1/2a. Furthermore, comparative analyzes before and after osmotic stress confirmed the increased potential for invasion (p < 0.05) in both serotypes (1/2a and 4b) after being submitted to high salt concentrations. The role of transcription regulators sigma B and PrfA in L. monocytogenes survival under osmotic stress condition was also evaluated. Microarray assay using lineage I and II strains showed increased transcription levels in 173 and 68 genes, respectively, when comparing the wild type strains to the mutant ΔsigB strain. This included genes related to virulence (internalina), survival under stress conditions and metabolic genes. The results confirm the ability of Lm strains in remain viable or even grow at low temperatures and in high osmotic pressure environments, regardless of serotype or origin. They also emphasize the need for effective measures to control this pathogen by food industry since it is possible that Lm strains survive under adverse conditions and also increase its virulence potential. The data also indicate the need for additional studies regarding the behavior of Lm in environments with modified sodium chloride concentration since the discussion about salt levels in foods is increasing worldwide. (AU) | |
| FAPESP's process: | 09/14618-0 - Virulence gene expression of Listeria monocytogenes isolates from clinical and food origin submitted to different growing conditions |
| Grantee: | Vinicius Buccelli Ribeiro |
| Support Opportunities: | Scholarships in Brazil - Doctorate |