Inhibition of Aspergillus carbonarius growth and Ochratoxin A production using lactic acid bacteria cultivated in an optimized medium.

The Gram-positive bacteria lactic acid bacteria (LAB) are used in the food industry but are also known for inhibiting certain food spoilage microorganisms, especially fungi. Sources of nitrogen (N) for culture media are generally organic and expensive. Many attempts have been made to formulate economical culture media with alternative N sources obtained from agricultural and industrial byproducts. This study describes the design and optimization of an inexpensive culture medium for Lactiplantibacillus plantarum (formerly Lactobacillus plantarum) MZ809351 strain B31. The culture medium was optimized using statistical experimental designs to identify the factors with the most significant effects on biomass concentration to reduce the overall cost, aiming to obtain a biomass concentration similar to that obtained with the reference LAB culture medium (de Man, Rogosa and Sharpe; MRS). Sodium acetate and magnesium sulfate were the most significant factors (p < 0.005), and their contents were reduced by 22 % and 40 %, respectively, without affecting biomass concentration. Malt germ extract (MGE) was used as an alternative nitrogen source to replace meat extract (ME) and proteose peptone (PP). Through these experiments, the composition of a culture medium that is less expensive than MRS broth was defined, which produced a biomass concentration (3.8 g/L) similar to that obtained with MRS medium. The inhibitory effects of two LAB strains isolated from the Ivory Coast and Mexico on the growth and production of ochratoxin A (OTA) in an ochratoxigenic fungus was tested. The minimum cellular concentration of the LAB to prevent the development of Aspergillus carbonarius Ac 089 and the production of OTA was determined in a model assay in Petri dishes. The conditions to inhibit the germination of A. carbonarius Ac 089 and the production of OTA were found. Using the optimized medium and a ratio of 2 × 104 LAB/spore (1 × 108 CFU/mL) strain B7 (L. plantarum MZ809351) and 2 × 103 LAB/spore (1 × 107 CFU/mL) strain B31 (L. plantarum MN922335) completely inhibited the growth of the fungus. A ratio of 2 × 105 LAB/spore (1 × 109 CFU/mL) was required to inhibit OTA production with strains B7 and B31. This study indicates the potential of cultivating LAB in an optimized and inexpensive culture medium for use as a biological control agent against ochratoxigenic fungi in food.

Frequency shift in topography of spontaneous brain rhythms from childhood to adulthood.

It has been described that the frequency ranges at which theta, mu and alpha rhythms oscillate is increasing with age. The present report, by analyzing the spontaneous EEG, tries to demonstrate whether there is an increase with age in the frequency at which the cortical structures oscillate. A topographical approach was followed. The spontaneous EEG of one hundredand seventy subjects was recorded. The spectral power (from 0.5 to 45.5 Hz) was obtained by means of the Fast Fourier Transform. Correlations of spatial topographies among the different age groups showed that older groups presented the same topographical maps as younger groups, but oscillating at higher frequencies. The results suggest that the same brain areas oscillate at lower frequencies in children than in older groups, for a broad frequency range. This shift to a higher frequency with age would be a trend in spontaneous brain rhythm development.

Narrow band quantitative and multivariate electroencephalogram analysis of peri-adolescent period.

BACKGROUND: The peri-adolescent period is a crucial developmental moment of transition from childhood to emergent adulthood. The present report analyses the differences in Power Spectrum (PS) of the Electroencephalogram (EEG) between late childhood (24 children between 8 and 13 years old) and young adulthood (24 young adults between 18 and 23 years old). RESULTS: The narrow band analysis of the Electroencephalogram was computed in the frequency range of 0-20 Hz. The analysis of mean and variance suggested that six frequency ranges presented a different rate of maturation at these ages, namely: low delta, delta-theta, low alpha, high alpha, low beta and high beta. For most of these bands the maturation seems to occur later in anterior sites than posterior sites. Correlational analysis showed a lower pattern of correlation between different frequencies in children than in young adults, suggesting a certain asynchrony in the maturation of different rhythms. The topographical analysis revealed similar topographies of the different rhythms in children and young adults. Principal Component Analysis (PCA) demonstrated the same internal structure for the Electroencephalogram of both age groups. Principal Component Analysis allowed to separate four subcomponents in the alpha range. All these subcomponents peaked at a lower frequency in children than in young adults. CONCLUSIONS: The present approaches complement and solve some of the incertitudes when the classical brain broad rhythm analysis is applied. Children have a higher absolute power than young adults for frequency ranges between 0-20 Hz, the correlation of Power Spectrum (PS) with age and the variance age comparison showed that there are six ranges of frequencies that can distinguish the level of EEG maturation in children and adults. The establishment of maturational order of different frequencies and its possible maturational interdependence would require a complete series including all the different ages.

First Report of Cassava virus X in Cassava in Venezuela.

Cassava (Manihot esculenta Crantz) is a vegetatively propagated tropical root crop. Viral infections have been identified as an important biotic component limiting cassava production (2). To survey for virus diseases, symptomatic samples of cassava plants were collected from the Venezuelan cassava production states Amazonas, Aragua, Barinas, Cojedes, Monagas, and Portuguesa. Mechanical transmissions to a differential host (Chenopodium quinoa) and a previously described double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) procedure (3) were used to test for the presence of Cassava virus X (CsVX). The DAS-ELISA procedure used gamma globulin diluted 1/2,000, conjugate diluted 1/2,000, and leaf sap extracts diluted 1/100 (1). CsVX and frog skin disease (detected graft inoculation tests with cultivar Secundina and electron microscopy) were detected in mixed infections in plants collected in Barinas. CsVX was not detected in any of the plants collected in the other surveyed areas. The low incidence of the virus (11.43%; 4 of 35 samples) suggests that CsVX has been introduced only recently via infected planting stock. Transmission of the virus is 100% when infected cuttings are used as propagation material. CsVX caused no symptoms on any of the cultivars examined in the field, and the occurrence of symptomless CsVX in Venezuela may result from the inadvertent use of cuttings from virus-infected plants. This is the first report of CsVX in cassava in Venezuela. References: (1) B. L. Nolt et al. Ann. Appl. Biol. 118:105, 1991. (2) B. L. Nolt et al. Plant Pathol. 41:348, 1992. (3) A. C. Velasco et al. 1994. Prog. Virol. Yuca, CIAT, Cali, Colombia.

First Report of Frog Skin Disease in Cassava (Manihot esculenta) in Venezuela.

Frogskin disease (FSD) is a disease of clonally propagated cassava (Manihot esculenta Crantz) and has been reported to reduce cassava yields significantly in South America (1). FSD is caused by an uncharacterized virus that is restricted to South America. The evidence indicates FSD is transmitted by stem cuttings and graft (3). However, little information is available on its distribution and incidence in Venezuela. Eighty-seven samples with virus-like symptoms were collected with the help of technical staff and producers in cassava-producing states: Amazonas (1 sample), Aragua (7 samples), Barinas (35 samples), Cojedes (8 samples), Monagas (19 samples), and Portuguesa (17 samples). In these states, the average daytime temperature was 26°C, but the average was higher (>28°C) during the dry season. Samples were collected during the rainy season because high temperatures and dry field conditions appeared to suppress symptom expression, while cooler conditions tended to favor symptom development (2). Roots of sampled cassava plants were examined for the presence of FSD. A single 70- to 80-cm-long stem cutting was taken from each plant and subdivided into four pieces. Two pieces were used as rootstocks in graft-inoculation tests with Secundina scions for FSD detection, and two pieces were potted in sterilized soil to be used in other tests. All potted and grafted plants were kept in the Vegetable Virology Laboratory of the Faculty of Agronomy (Universidad Central de Venezuela), at an average temperature of 24°C and 80% relative humidity. FSD-infected plants were identified by mosaic symptoms on Secundina scions and the presence of 80-nm spherical viral particles. Most FSD-infected cultivars expressed only root symptoms. However, in the case of Secundina cvs. MCOL 22 and MCOL 113, foliar symptoms were also detected (1). FSD was found in a simple infection in one cassava sample from Aragua State (14.3% incidence, 1 of 7 samples) and in four cassava samples from Barinas State (11.4% incidence, 4 of 35 samples) associated with Cassava virus X (detected by double-antibody sandwich enzyme-linked immunosorbent assay). To our knowledge, this is the first report of FSD detection in Venezuela. References: (1) E. A. Frison et al. Informe Anual. CIAT, Cali, Colombia, 1995. (2) B. L. Nolt et al. Plant Pathol. 41:384, 1992. (3) Technical Guidelines for the Safe Movement of Cassava Rome. FAO/IBPGR. p. 10-27, 1991.

Ah receptor-based chemical screening bioassays: application and limitations for the detection of Ah receptor agonists.

The aromatic hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates many of the biologic and toxicologic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin) and related chemicals. Here we utilized two AhR-dependent bioassay systems as screening tools to identify novel AhR agonists and to detect the presence of AhR agonists in sample extracts. These assays measure the ability of a chemical to activate AhR DNA binding in vitro (GRAB bioassay) or AhR-dependent (luciferase) gene expression in cultured cells (CALUX bioassay). Known AhR agonists (halogenated and nonhalogenated aromatic hydrocarbons) were positive in both assays, whereas the AhR antagonist alpha-naphthoflavone exhibited agonist activity only in the GRAB assay. In vitro GRAB analysis has identified several imidazoline receptor ligands and beta-carbolines as AhR agonists and also revealed the presence of AhR agonist activity in crude DMSO extracts of commercial newspapers. In contrast to their positive activity in the GRAB assay, the majority of these chemicals/extracts were only weakly active or inactive in the cell-based CALUX assay. Our results not only reveal that the ability of a chemical to activate the AhR in vitro does not necessarily correlate with its ability to induce gene expression in intact cells, but the high level of false positives obtained with the GRAB assay clearly demonstrates its inability to accurately identify AhR agonists or agonist activity. Screening of unknown chemicals, chemical classes, and samples for AhR agonist activity will require the use of intact cell bioassays.

Duodenogastric reflux and reflux esophagitis.

Twenty-seven patients with gastroesophageal reflux were prospectively investigated to define the role of duodenogastric reflux in the development of reflux esophagitis. Duodenogastric reflux was detected and quantified by pH monitoring of the gastric environment 5 cm distal to the distal esophageal sphincter. Alkaline duodenogastric reflux was identified by the occurrence of spontaneous, intense gastric alkalinization during fasting periods. Patients with reflux with esophagitis were distinguished from those without esophagitis by having fewer of these episodes and, consequently, more acid stomachs than had patients without esophagitis. As previously shown, refluxers with esophagitis also had more frequent acid gastroesophageal reflux and prolonged gastric emptying. These findings suggest that refluxers with esophagitis have a functional gastropyloric disturbance resulting in delayed gastric emptying, decreased frequency of alkaline duodenogastric reflux episodes, and more frequent acid gastroesophageal reflux than do refluxers without esophagitis.