Resistance of Corynebacterium pseudotuberculosis in the Brazilian semiarid environment

ABSTRACT: The semiarid northeast of Brazil contains a unique biome known as caatinga, with a maximum temperature of 40 ºC and a relativity humidity of 56%. The caatinga is characterized by a variety of plants, including Cereus jamacaru Dc (mandacaru), Poincianella microphylla Mart. ex G. Don (catingueira), Pilosocereus gounellei FAC Weber (xique-xique) and Mimosa tenuiflora (Willd.) Poir (jurema preta). Sheep and goat industries are economically strong in that region, despite the fact that caseous lymphadenitis is highly prevalent. The aim of the present study was to assess the survival and biofilm production of Corynebacterium pseudotuberculosis isolates in the environment and under controlled temperatures (28°C, 37°C and 42°C) under different surfaces (plants, soil, wood, wire and thorns). In addition, we investigated the effects of applying the disinfectants chlorhexidine, hypochlorite and quaternary ammonia in soil, tiles, wood and vegetation cover. Four strains of C. pseudotuberculosis were selected (two from goats and two from sheep) for inoculation according to their in vitro biofilm production. Adherence to microplates was used to assess the biofilm-forming ability of the bacteria. Lower survival rates were observed when isolates of C. pseudotuberculosis were subjected to a temperature of 42°C. In terms of caatinga biome plants, contamination of jurema-preta plants resulted in the lowest survival rates. The disinfectant quaternary ammonia promoted a lower inoculum survival in all surfaces. The disinfectants and the higher temperature contributed to the reduction of biofilm production in isolates of C. pseudotuberculosis. knowledge of these patterns is important for the establishment of disease control measures, given the questionable efficacy of the treatment and the immuno-prophylaxis of caseous lymphadenitis.

Models of Early Spring Survival of Wheat Leaf Rust in the Central Great Plains

Severe leaf rust epidemics, which result in economic yield reductions in the Great Plains wheat-producing region of the United States, are usually initiated by Puccinia recondita f. sp. tritici inoculum that has survived in the local field from the previous wheat crop until early spring. Models were developed for an epidemic year beginning at physiological maturity of one wheat crop to maturity of the following wheat crop. Meteorological variables for periods prior to final tiller development of the wheat crop during 1980 to 1992 at several sites in the central Great Plains winter-wheat-production area were used to model inoculum survival from one wheat crop until early spring of the next crop. Stepwise multiple regression was used to identify weather variables that explained the most variation in inoculum survival at the final tiller development wheat growth stage. Inoculum survival was recorded on a 0 to 9 scale with 0 indicating no survival and 9 indicating inoculum on all wheat plants in the field. Independent variables used in development of models were daily deviations from the 10-year average of maximum and minimum temperature, fungal temperature equivalence function, cumulative fungal temperature function, precipitation, cumulative precipitation, and snow cover averaged for 10-day periods prior to dates inoculum forecasts were desired. Models were constructed to forecast inoculum survival from data collected prior to fall wheat planting, the beginning of winter dormancy of the wheat, and the final tiller development wheat growth stage. Of the observed occurrences of leaf rust overwintering, 70% were forecast by models constructed using weather data prior to wheat planting decision time. Overwintering could be forecast by models constructed with data prior to the wheat entering winter dormancy 80% of the time. Models constructed with data collected prior to final tiller development in the spring forecast overwintering of leaf rust inoculum 95% of the time. Results from these models will be used to develop forecasts of leaf rust epidemics and resulting yield reductions.

Survival of Listeria monocytogenes in Refrigerated Cultured Milks and Yogurt

Skim milks containing Listeria monocytogenes were fermented at 21, 30, 37 or 42°C for 15 h with Streptococcus lactis, S. cremoris, S. thermophilus, Lactobacillus bulgaricus or L. bulgaricus plus S. thermophilus (LBST). Amounts of inocula were 5.0, 1.0, 0.5 or 0.1%. Yogurt mix was inoculated with L. monocytogenes and fermented at 45°C for 5 h. Cultured skim milks and yogurt were stored at 4°C and sampled weekly to monitor survival of L. monocytogenes and the pH. Yogurt was sampled ca. every 3 d for enumeration of L. monocytogenes and determination of pH. Results show that L. monocytogenes survived longest in skim milks fermented with S. thermophilus, ranging from 4 weeks in skim milk fermented at 42°C with a 5.0% inoculum (final pH 4.62) to 37 weeks in skim milk fermented at 37°C with a 1.0% inoculum (final pH 4.52). When skim milks were fermented with S. lactis, L. monocytogenes survived from 2 weeks (5.0% inoculum, 30°C incubation, final pH 4.20) to more than 13 weeks (0.1% inoculum, 21°C incubation, final pH 4.70). L. monocytogenes survived from 4 (final pH 4.36) to 13 (final pH 5.30) weeks in milk fermented with S. cremoris. L. bulgaricus was the most detrimental to L. monocytogenes; the pathogen survived only 3 d to 1 week in the skim milk fermented at 37°C with 0.1 % inoculum. Survival of L. monocytogenes in milk fermented with LBST culture ranged from 1 (final pH 3.93) to 12 (final pH 4.41) weeks in those skim milks in which the organism survived the fermentation process. L. monocytogenes survived yogurt manufacture and from 1 (final pH 4.13) to 12 (final pH 3.93) d during refrigerated storage of the product.