Published Article / The development of tolerance to low pH levels and the existence of cross-resistance may promote survival of bacteria in acidic foodstuff and in acidic environments such as the human stomach, in so doing escalating the probability of food poisoning. Similar to antimicrobial resistance developing, there is growing concern that effectiveness of organic acids may decrease as a result of the emergence of acid-tolerant food-borne pathogens. The objectives of this study were to determine the development of acid tolerance in selected food-borne pathogenic bacteria and to explore the activity of organic acids against acid tolerant pathogens. Bacterial strains were screened for acid-tolerance and susceptible strains were induced through exposure to increasing concentrations of an inorganic acid, as well as acidic foodstuffs. Susceptibility to six organic acids at various pH levels was assessed in order to evaluate the possible relationship between altered antimicrobial activity and acid tolerance. Salmonella enterica sv. Enteritidis ATCC 13076 and Escherichia coli ATCC 25922 were found to rapidly develop acid tolerance, while intrinsic acid tolerance was noted in Salmonella enterica sv. Typhimurium ATCC 14028. Pseudomonas aeruginosa ATCC 27853 demonstrated intermediate intrinsic acid tolerance. As expected, pH played a significant role in inhibitory activity of the organic acids as these compounds exhibit optimum antimicrobial activity at a lower pH (pH ≤5). It is, however, necessary to further elucidate the two-way role of pH in foodstuff concomitant to the addition of an organic acid.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / Este trabalho teve como objetivo estudar a utilizaÃÃo de glicerol oriundo da indÃstria do biodiesel (glicerol bruto) como substrato em ensaios fermentativos para a produÃÃo de etanol. Os ensaios foram realizados em mesa agitadora com velocidade de 200 rpm, nas temperaturas de 30 e 37 ÂC, respectivamente para os microrganismos Saccharomyces sp. 1238 e Escherichia coli 224 ATCC 25922. Nos experimentos realizados com a levedura Saccharomyces sp., variaram-se as concentraÃÃes de glicerol adicionado ao meio fermentativo em 0,5; 1,0 e 5,0 % v/v e fixou-se o volume de inÃculo em 1 % m/v. Observou-se que o microrganismo Saccharomyces sp. nÃo utilizou glicerol como fonte de carbono para produÃÃo de etanol, porÃm em ensaios teste com glicose P.A., observou-se que este substrato foi rapidamente consumido pelo microrganismo apresentando uma produÃÃo de etanol de 5,5 g/L. Nas fermentaÃÃes com a bactÃria Escherichia coli, variou-se a concentraÃÃo de glicerol adicionado ao meio fermentativo em: 1, 10, 15 e 20 g/L. Pela avaliaÃÃo da influÃncia da concentraÃÃo de substrato no meio atravÃs dos resultados obtidos, pode-se concluir que a melhor condiÃÃo para a produÃÃo de etanol com esse microrganismo foi a concentraÃÃo inicial de 10 g/L de glicerol. O consumo de glicerol pela bactÃria Escherichia coli foi afetado pela variaÃÃo deste substrato. Observou-se que o etanol foi produzido a partir de 8 h de cultivo nas fermentaÃÃes tanto com glicerol bruto quanto P.A. nas concentraÃÃes de 10, 15 e 20 g/L adicionado ao meio de cultivo. Observou-se tambÃm a formaÃÃo de Ãcido acÃtico nas primeiras horas da fermentaÃÃo. A produÃÃo de Ãcido acÃtico foi baixa, atingindo a concentraÃÃo de 0,15 g/L na fermentaÃÃo utilizando 10 g/L de glicerol bruto. Analisando os dois microrganismos estudados, verificou-se que apenas a bactÃria Escherichia coli 224 ATCC 25922 mostrou-se adequada ao objetivo desta pesquisa, jà que com a levedura nÃo foi produzido etanol em quantidade significativa. / The aim of this work was to investigate the use of glycerol from biodiesel industry (raw glycerol) as a substrate in fermentation assays for production of ethanol. The assays were performed in shaker with agitation of 200 rpm, at temperatures of 30 and 37 ÂC, respectively for the microorganisms Saccharomyces sp. 1238 and 224 Escherichia coli ATCC 25922. In experiments with yeast Saccharomyces sp., it was varied concentrations of glycerol from fermentation medium at 0.5, 1.0 and 5.0 % v/v and the inoculum was set to 1% w/v. It was observed that the microorganism Saccharomyces sp. could not use glycerol as carbon source for ethanol production, but in assays using glucose, this substrate was rapidly consumed by the microorganism achieving an ethanol production of 5.5 g/L. It was varied the concentration of glycerol added to the fermentation medium: 1, 10, 15 and 20 g/L when Escherichia coli was used. By analyzing the influence of substrate concentration in fermentations, it can be concluded that the best condition for ethanol production, with this microorganism, was initial concentration of glycerol of 10 g/L. The consumption of glycerol by Escherichia coli was affected by the change of substrate concentration. It was observed that ethanol was produced after 8 h of fermentation with both raw and PA glycerol at 10, 15 and 20 g/L. It also observed the formation of acetic acid in the first hours of fermentation. The production of acetic acid was low, reaching a concentration of 0.15 g/L in fermentation using 10 g/L of raw glycerol. Analyzing the two microorganisms studied, it was found that only 224 bacteria Escherichia coli ATCC 25922 was adequate to the aim of this research, since the yeast was not produced ethanol in significant amounts.