Condições para indução do estado viável não cultivável (VNC) em Salmonella e Escherichia coli

• Autor(a) principal: Floresta, Flávia Arruda
• Data de Publicação: 2006
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/5332
• topic: Salmonella; Escherichia coli; Salmonella; Escherichia coli; CNPQ::CIENCIAS AGRARIAS::CIENCIA E TECNOLOGIA DE ALIMENTOS::CIENCIA DE ALIMENTOS::MICROBIOLOGIA DE ALIMENTOS

The effect of sodium chorine on the growth and survival of Salmonella and Escherichia coli and the role of salt concentration in the induction of the viable but non culturable (VNC) state was evaluated. Salmonella CCS3 and E. coli CCS4, isolated from swine carcasses, and a reference strain of Salmonella and E. coli were used in this study. All strains showed smaller maximum growth rates when cultured in Brain Heart Infusion (BHI) with different NaCl concentrations than in control treatments (BHI without NaCl). Sodium chloride affected log and stationary phase cultures of Salmonella and E. coli differently. Salmonella and E. coli from exponentially growing cultures showed reduction in the number of colony forming units (CFU/mL) after ten days of storage at 4 °C in BHI medium. Stationary phase cells of Salmonella and E. coli were not affected by NaCl concentrations up to 0,68 M and 1.02 M, respectively. In BHI without salt and BHI with 0,17 M of NaCl, growth was observed for both log and stationary phase cells of the four strains tested. In phosphate Butterfield solution (PBS) without salt or with 0,17 M of NaCl, log phase cells of Salmonella and E. coli did not grow, while concentrations of 0,68 M and 1,02 M NaCl for Salmonella and 1,02 M and 1,28 M NaCl for E. coli induced a significant loss of culturability at the same time and temperature of incubation. When stationary phase cells of the four strains were incubated in PBS, the number of CFU/mL was similar regardless of the NaCl concentration used. Some log phase cells of the four strains lost culturability but maintained viability at higher NaCl concentrations in BHI and PBS, suggesting that Salmonella and E. coli entered the VNC state. Scanning electron microscopy indicated morphological changes in E. coli CCS4 cells under osmotic stress. In BHI medium without salt or with 0,17 M and 1,02 M of NaCl, filamentous growth was observed, while in BHI with 1,28 M NaCl, the cells became smaller or lysed. In PBS, all conditions tested resulted in cell size reduction and at 1,28 M NaCl was observed the transition of the cells to the coccoid form. These results suggest that osmotic stress and refrigeration temperature induce the VNC state in isolates of Salmonella and E. coli obtained from swine carcasses.