Assessment of endophytic yeast diversity in rice leaves by a culture-independent approach.

Endophytic microorganisms inhabit internal plant tissues in the host plant without causing any symptoms or negative effects. Although the diversity of endophytes has been evaluated by both culture-dependent and culture-independent methods, less information is available on yeast communities. Therefore, in this study a culture-independent method was used to examine endophytic yeasts associated with rice leaves based on the large subunit of ribosomal DNA using a semi-nested PCR technique. Sequence analysis indicated that the colonization frequency and the relative species frequency (RF) of endophytic yeast phylotypes were 0.41 and 0.06, respectively, and the majority of the yeast phylotypes were basidiomycetous yeasts. The phylotypes were designated as five known species (Cryptococcus victoriae, Debaryomyces hansenii, Debaryomyces vindobonensis, Meyerozyma guilliermondii and Pseudozyma antarctica), together with seventeen phylotypes closest to Candida metapsilosis, Cryp. foliicola, Cryp. laurentii, Pseudozyma abaconensis, Pseudozyma aphidis and Trichosporon asahii, among which some could be novel species. The most prevalent phylotypes were those closest to Cryp. foliicola (47.5 % RF) followed by D. hansenii (22.8 % RF) and P. antarctica (16.8 % RF). The presence of the phylotypes related to species known for their potential applications as biocontrol agents and plant growth promoting hormone producers suggests that they may have valuable applications. In addition, our findings revealed the occurrence of novel phylotypes at high frequency, which should encourage extensive studies to discover novel yeast species and to understand their roles in the rice leaves.

Calidad bacteriológica y detección de Bacillus cereus toxigénicos en arroz blanco cocido expendido en el área metropolitana de la provincia de San José, Costa Rica

El gran consumo de arroz a nivel mundial es uno de los factores que favorece su implicación en brotes de origen alimentario y de uno de los patógenos más importantes ligado a este producto como el Bacillus cereus El objetivo del presente trabajo fue evaluar la calidad microbiológica de 50 muestras de arroz blanco cocido expendido en restaurantes de área Metropolitana de San José Costa Rica, incluyendo la determinación del recuento total aerobio mesófilo, Número Más Probable de coliformes totales, fecales y E. coli, B. cereus así como de detección de sus genes nheA, nheB, y nheC. Para el análisis bacteriológico se siguieron los procedimientos descritos en el Compendio de Métodos para el Examen Microbiológico de Alimentos y para la detección de los genes se utililzó un PCR múltiplex y la metodología descrita por Hansen et al., 2001. De las muestras analizadas 46% fueron positivas por coliformes totales, 34% por coliformes fecales, 16% por E. coli, 10% por B. cereus y un 8% por B. cereus toxigénico Lo anterior sugiere que el consumo de arroz blanco en restaurantes puede representar un riesgo para la salud pública y que es necesario implementar mejoras con el fin de brindarle al consumidor un producto inocuo y de mejor calidad.

Bacteriological quality and toxigenic Bacillus cereus detection in cooked white rice sold at the Metropolitan Area of San José, Costa Rica.. The wide use of rice is one of the factors that favors its implication in food borne diseases, and one of the most important pathogens associated to it is Bacillus cereus. The aim of this work was to evaluate the microbiological quality of 50 samples of white cooked rice sold in restaurants at the Metropolitan Area of San José, Costa Rica, including the determination of the total aerobic plate count, the Most Probable Number of total and fecal coliforms and Escherichia coli. MPN of Bacillus cereus and the detection of nheA, nheB and nHeC genes, associated to its toxicity, was also performed. Procedures described in the Compendium of Methods for the Microbiological Examination of Foods were followed for the bacteriological analysis, multiplex PCR was used for the detection of genes following the methodology described by Hansen et al, 2001. 46% of the samples analysed were positive for total coliforms, 34% for fecal coliforms, 16% for E. coli and 10% for B. cereus, being 8% toxigenic. These facts suggest that white cooked rice may represent a risk for Pubic Health and that improvements shall be performed in order to offer a safe and high quality product to consumers.

[Bacteriological quality and toxigenic Bacillus cereus detection in cooked white rice sold at the metropolitan area of San José, Costa Rica]. / Calidad bacteriológica y detección de Bacillus cereus toxigénicos en arroz blanco cocido expendido en el área metropolitana de la provincia de San José, Costa Rica.

The wide use of rice is one of the factors that favors its implication in food borne diseases, and one of the most important pathogens associated to it is Bacillus cereus. The aim of this work was to evaluate the microbiological quality of 50 samples of white cooked rice sold in restaurants at the Metropolitan Area of San José, Costa Rica, including the determination of the total aerobic plate count, the Most Probable Number of total and fecal coliforms and Escherichia coli. MPN of Bacillus cereus and the detection of nheA, nheB and nHeC genes, associated to its toxicity, was also performed. Procedures described in the Compendium of Methods for the Microbiological Examination of Foods were followed for the bacteriological analysis, multiplex PCR was used for the detection of genes following the methodology described by Hansen et al, 2001. 46% of the samples analysed were positive for total coliforms, 34% for fecal coliforms, 16% for E. coli and 10% for B. cereus, being 8% toxigenic. These facts suggest that white cooked rice may represent a risk for Pubic Health and that improvements shall be performed in order to offer a safe and high quality product to consumers.