The possibility of using the polymerase chain reaction (PCR) to speed up and specify the detection of aflatoxigenic fungi isolated from feed was investigated. The method, applied to 2 genes encoding the biosynthesis of aflatoxins (apa-2 and ver-1), was optimized on two collection cultures (Aspergillus flavus CCM F-108 and A. parasiticus CCM F-550). The specificity of the optimized PCR method was proved on collection cultures of different kinds of fungi. Fifty feed samples out of which 18 showed positive findings of aflatoxigenic fungi on an Aspergillus Flavus and Parasiticus Agar (AFPA) medium were tested. Isolated strains of Aspergillus strains were verified using the PCR method; its reaction products were detected in 1% agarose gel by electrophoresis. The results almost exclusively matched those gained from the AFPA medium.
AbstractČ������� L., Z������ I., M��������� P., V�������� J. (2003): Effect of pH and water activity on the growth of Arcobacter sp. in culture. Czech J. Food Sci., 21: 203-209.The effect was studied of pH value and water activity (a w ) on the growth of Arcobacter butzleri and Arcobacter cryaerophilus in culture media at 30°C. Various weak organic acids were used to achieve target pH, and different humectants were used to control a w . Generally, the growth of arcobacters was inhibited at medium pH. Compared to propionic, lactic, malic and ascorbic acids (pH 5.5-5.0), formic, citric and tartaric acids in the pH range of 6.0-5.5 were more inhibitory to both arcobacter species. Both arcobacter strains were extremely sensitive to broth environment with a w values of < 0.980 using NaCl, glycerol and sucrose as humectants. This sensitivity to a w and pH may well be an important constraint for the distribution and survival of Arcobacter sp. in the environment, particularly in foods and food products.
The influence of weak organic acids and trisodium citrate in combination with a high or a reduced water activity (aw) was investigated when a population of Arcobacter butzleri was exposed to a low concentration of acetic or citric acid, and trisodium citrate combined with high (0.993) and reduced (0.977) aw in culture broth at 30 degrees C. Regardless of water activity, acetic and citric acid (> 0.2%) inhibited the growth of A. butzleri with no viable cells detected after 4-5 h of incubation. Enhanced survival was found at reduced aw with addition of acetic acid. In contrast, after exposure to citric acid in combination with reduced aw inactivation was more rapid than that after being exposed to high water activity. Incorporation of trisodium citrate in combination with reduced aw (0.977) would probably not confer any extra protection. Concentrations of organic acid widely used in meat decontamination processing represent feasible tools for reducing A. butzleri contamination and hence the risk of Arcobacter infection.
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