José Roberto Villagómez-Ibarra

Incidence and behavior of Salmonella and Escherichia coli on whole and sliced zucchini squash (Cucurbita pepo) fruit.

The incidence of coliform bacteria (CB), thermotolerant coliforms (TC), Escherichia coli, and Salmonella was determined for zucchini squash fruit. In addition, the behavior of four serotypes of Salmonella and a cocktail of three E. coli strains on whole and sliced zucchini squash at 25+/-2 degrees C and 3 to 5 degrees C was tested. Squash fruit was collected in the markets of Pachuca city, Hidalgo State, Mexico. CB, TC, E. coli, and Salmonella were detected in 100, 70, 62, and 10% of the produce, respectively. The concentration ranged from 3.8 to 7.4 log CFU per sample for CB, and >3 to 1,100 most probable number per sample for TC and E. coli. On whole fruit stored at 25+/-2 degrees C or 3 to 5 degrees C, no growth was observed for any of the tested microorganisms or cocktails thereof. After 15 days at 25+/-2 degrees C, the tested Salmonella serotypes had decreased from an initial inoculum level of 7 log CFU to <1 log, and at 3 to 5 degrees C they decreased to approximately 2 log. Survival of E. coli was significantly greater than for the Salmonella strains at the same times and temperatures; after 15 days, at 25+/-2 degrees C E. coli cocktail strains had decreased to 3.4 log CFU per fruit and at 3 to 5 degrees C they decreased to 3.6 log CFU per fruit. Both the Salmonella serotypes and E. coli strains grew when inoculated onto sliced squash: after 24 h at 25+/-2 degrees C, both bacteria had grown to approximately 6.5 log CFU per slice. At 3 to 5 degrees C, the bacterial growth was inhibited. The squash may be an important factor contributing to the endemicity of Salmonella in Mexico.

Bioremediation model for atrazine contaminated agricultural soils using phytoremediation (using Phaseolus vulgaris L.) and a locally adapted microbial consortium

ABSTRACT The objective of the present study was to examine a biological model under greenhouse conditions for the bioremediation of atrazine contaminated soils. The model consisted in a combination of phytoremediation (using Phaseolus vulgaris L.) and rhizopheric bio-augmentation using native Trichoderma sp., and Rhizobium sp. microorganisms that showed no inhibitory growth at 10,000 mg L−1 of herbicide concentration. 33.3 mg of atrazine 50 g−1 of soil of initial concentration was used and an initial inoculation of 1 × 109 UFC mL−1 of Rhizobium sp. and 1 × 105 conidia mL−1 of Trichoderma sp. were set. Four treatments were arranged: Bean + Trichoderma sp. (B+T); Bean + Rhizobium sp. (BR); Bean + Rhizobium sp. + Trichoderma sp. (B+R+T) and Bean (B). 25.51 mg of atrazine 50 g−1 of soil (76.63%) was removed by the B+T treatment in 40 days (a = 0.050, Tukey). This last indicate that the proposed biological model and methodology developed is useful for atrazine contaminated bioremediation agricultural soils, which can contribute to reduce the effects of agrochemical abuse.

Behavior of 11 Foodborne Bacteria on Whole and Cut Mangoes var. Ataulfo and Kent and Antibacterial Activities of Hibiscus sabdariffa Extracts and Chemical Sanitizers Directly onto Mangoes Contaminated with Foodborne Bacteria

The behavior of foodborne bacteria on whole and cut mangoes and the antibacterial effect of Hibiscus sabdariffa calyx extracts and chemical sanitizers against foodborne bacteria on contaminated mangoes were investigated. Mangoes var. Ataulfo and Kent were used in the study. Mangoes were inoculated with Listeria monocytogenes, Shigella flexneri, Salmonella Typhimurium, Salmonella Typhi, Salmonella Montevideo, Escherichia coli strains (O157:H7, non-O157:H7 Shiga toxin-producing, enteropathogenic, enterotoxigenic, enteroinvasive, and enteroaggregative). The antibacterial effect of five roselle calyx extracts (water, ethanol, methanol, acetone, and ethyl acetate), sodium hypochlorite, colloidal silver, and acetic acid against foodborne bacteria were evaluated on contaminated mangoes. The dry extracts obtained with ethanol, methanol, acetone, and ethyl acetate were analyzed by nuclear magnetic resonance spectroscopy to determine solvent residues. Separately, contaminated whole mangoes were immersed in five hibiscus extracts and in sanitizers for 5 min. All foodborne bacteria attached to mangoes. After 20 days at 25 ± 2°C, all foodborne bacterial strains on whole Ataulfo mangoes had decreased by approximately 2.5 log, and on Kent mangoes by approximately 2 log; at 3 ± 2°C, they had decreased to approximately 1.9 and 1.5 log, respectively, on Ataulfo and Kent. All foodborne bacterial strains grew on cut mangoes at 25 ± 2°C; however, at 3 ± 2°C, bacterial growth was inhibited. Residual solvents were not detected in any of the dry extracts by nuclear magnetic resonance. Acetonic, ethanolic, and methanolic roselle calyx extracts caused a greater reduction in concentration (2 to 2.6 log CFU/g) of all foodborne bacteria on contaminated whole mangoes than the sodium hypochlorite, colloidal silver, and acetic acid. Dry roselle calyx extracts may be a potentially useful addition to disinfection procedures of mangoes.

Identification of an Indigenous Atrazine Herbicide Tolerant Microbial Consortium in Beans (Phaseolus vulgaris L.) as a Potential Soil Bioremediator

The present article reports the isolation and identification of atrazine-tolerant strains of indigenous microorganisms recovered from three representative agricultural sites representing agronomic characteristics of the Tulancingo Valley, Central part of Mexico (disturbed and undisturbed). Biochemical and morphological tests were performed for microorganism’s identification and the minimum inhibitory concentration assay was followed to assess atrazine tolerance. Results showed the microorganism populations varied from 10-5 to 10-6 UFC g-1 of soil for bacteria and 104 - 105 conidia g-1 of soil for fungi. The bacterial genera isolated and identified were: Agrobacterium sp., Bacillus sp., Erwinia sp., Micrococcus sp., Pediococcus sp., Rhizobium sp., Serrantia sp. and Sphingomonas sp. Identified fungal genera were: Alternaria sp., Aspergillus sp., Mucor sp., Cladosporium sp., Penicillium sp., Fusarium sp. and Trichoderma sp. Tests for herbicide tolerance indicate the isolated microorganisms do not show inhibitory growth at 500 to 2,500 ppm of atrazine concentrations under laboratory conditions. The strains of the fungal genera and Rhizobium sp. showed greater tolerance rates to atrazine, based on their growth without inhibition in the presence of 5,000 to 10,000 ppm of the agrochemical. Results suggest the isolated microorganisms may be useful as a viable inoculum for bioremediation purposes in agricultural atrazine-contaminated soils.