Growth kinetics of Escherichia coli O157: H7 on the epicarp of fresh vegetables and fruits

ABSTRACT Despite the increasing reports on the incidence of fresh vegetables and fruits as a possible vehicle for human pathogens, there is currently limited knowledge on the growth potential of Escherichia coli O157:H7 on different plant substrates. This study analyzed the selective adhesion and growth of E. coli O157:H7 on chili habanero (Capsicum chinense L.), cucumber (Cucumis sativus), radish (Raphanus sativus), tomato (Lycopersicon esculentum), beet (Beta vulgaris subsp. vulgaris), and onion (Allium cepa L.) under laboratory conditions. The Gompertz parameters were used to determine the growth kinetics. Scanning electron microscopy was used to visualize the adhesion of E. coli O157:H7 on the epicarp of the samples. Predictive models were constructed to compare the growth of E. coli O157:H7 on the samples with different intrinsic factors and to demonstrate the low selectivity of the pathogen. No significant difference was observed in the lag-phase duration (LPD), generation time (GT), and exponential growth rate (EGR) of the pathogen adhered to the samples. The interaction between the microorganism and the substrate was less supportive to the growth of E. coli O157:H7 for onion, whereas for tomato and cucumber, the time for the microorganism to attain the maximum growth rate (M) was significantly longer than that recorded for other samples.

Molecular methods for diversity assessment among xanthomonads of Bulgarian and Macedonian pepper

ABSTRACT Bacterial spot is an important disease of pepper in Bulgaria and Macedonia. For characterization of Xanthomonas species associated with bacterial spot, 161 strains were collected from various field pepper-growing regions. Among them, 131 strains were identified as Xanthomonas euvesicatoria and 30 as Xanthomonas vesicatoria using species-specific primers and polymerase chain reaction followed by restriction fragment length polymorphism analysis. To assess the genetic diversity of the strains, two methods (Random Amplified Polymorphic DNA and Repetitive Element Palindromic-Polymerase Chain Reaction) were applied. Discriminatory index was calculated and analysis of molecular variance was carried out.Combined random amplified polymorphic DNA analysis of the X. euvesicatoria strains with primers CUGEA-4 and CUGEA-6 had greater discriminative power (0.60) than repetitive element palindromic-polymerase chain reaction with ERIC and BOX A1R primers, which makes this method applicable for strain diversity evaluation. Discrimination among the X. vesicatoria strains was achieved by the use of ERIC primers and only for the Bulgarian strains. The results demonstrated that X. euvesicatoria was more diverse than X. vesicatoria and heterogeneity was observed mainly in the Bulgarian populations. According to the analysis of molecular variance, genetic variations in X. euvesicatoria were observed among and within populations from different regions, while the differences between the two countries were minor. Following the principal coordinates analysis, a relation between the climatic conditions of the regions and a genetic distance of the populations may be suggested.

Microbiological quality of Argentinian paprika / Calidad microbiológica del pimentón argentino

The aim of this study was to evaluate the microbiological quality of paprika produced in Catamarca, Argentina. Microbiological analyses were carried out for the enumeration of total aerobic mesophilic bacteria, coliforms, yeasts and molds, and the detection of Salmonella in samples obtained from different local producers during three consecutive years. The mycobiota was identified paying special attention to the mycotoxigenic molds. Standard plate counts of aerobic mesophilic bacteria ranged from 2.7 x 10(5) to 3.7 x 10(7)CFU/g. Coliform counts ranged from <10 to 8.1 x 10(4) CFU/g. Salmonella was not detected in any of the samples tested. Fungal counts (including yeasts and molds) ranged between 2 x 10² and 1.9 x 10(5) CFU/g. These results showed a high level of microbial contamination, exceeding in several samples the maximum limits set in international food regulations. The study of the mycobiota demonstrated that Aspergillus was the predominant genus and Aspergillus niger (potential producer of ochratoxin A) the most frequently isolated species, followed by Aspergillus flavus (potential producer of aflatoxins). Other species of potential toxigenic fungi such as Aspergillus ochraceus, Aspergillus westerdijkiae, Penicillium chrysogenum, Penicillium crustosum, Penicillium commune, Penicillium expansum and Alternaria tenuissima species group were encountered as part of the mycobiota of the paprika samples indicating a risk of mycotoxin contamination. A. westerdijkiae was isolated for the first time in Argentina.

El pimentón es considerado una de las especias más proclives a contaminarse con diversos tipos de microorganismos, incluyendo patógenos como Salmonella y hongos capaces de producir micotoxinas. Existen muy pocos datos acerca de la contaminación microbiana del pimentón producido en nuestro país. El objetivo del presente trabajo fue evaluar la calidad microbiológica del pimentón (Capsicum annum L.) producido en la provincia de Catamarca, una de las principales zonas productoras del norte argentino. Se realizó el recuento de bacterias aerobias mesófilas, coliformes totales y mohos y levaduras, y la búsqueda de Salmonella en muestras obtenidas de diferentes establecimientos productores locales durante 3 años consecutivos. Se identificaron todas las cepas fúngicas (1.622 aislamientos) a nivel de género y se determinaron las especies pertenecientes a los géneros potencialmente toxinógenos. Los recuentos totales de bacterias aerobias mesófilas variaron entre 2,7 x 10(5)y3,7 x 10(7)UFC/g. Los coliformes totales estuvieron en el rango de < 10 a 8,1 x 10(4) UFC/g. Salmonella no fue detectada en ninguna de las muestras analizadas. Los resultados obtenidos muestran un alto nivel de contaminación, que excede en varias de las muestras los límites máximos establecidos en las regulaciones alimentarias internacionales. El estudio de la micobiota demostró que Aspergillus fue el género predominante. Otros géneros encontrados fueron Cladosporium, Rhizopus, Alternaría y Penicillium. Aspergillus niger (potencial productor de ocratoxina A) fue la especie aislada con mayor frecuencia, seguida de Aspergillus flavus (potencial productor de aflatoxinas). También se encontraron otras especies toxinógenas, lo que indica un riesgo potencial de contaminación con micotoxinas. Aspergillus westerdijkiae fue aislado por primera vez en Argentina.

Management of blight of bell pepper (Capsicum annuum var. grossum) caused by Drechslera bicolor

Abstract Sweet or bell pepper is a member of the Solanaceae family and is regarded as one of the most popular and nutritious vegetable. Blight, in the form of leaf and fruit blight, has been observed to infect bell pepper crops cultivated at the horticulture farm in Rajasthan College of Agriculture, Udaipur, India. Based on disease severity, we attempted to curb this newly emerged problem using different fungicides, plant extracts, bio-control agents, and commercial botanicals against the fungus in laboratory and pot experiments. Bio-control agent Trichoderma viride and plant growth promoting Rhizobacteria (PGPR) isolate Neist-2 were found to be quite effective against bell pepper blight. All evaluated fungicides, botanicals, commercial botanicals, and bio-control agents in vitro were further studied as seed dressers and two foliar sprays at ten days interval in pot experiments. The combinations of Vitavax, PGPR isolate Neist-2, and Mehandi extract were found to be very effective against bell pepper blight followed by Vitavax, T. viride, and Mehandi extract used individually. All treatments in the pot experiments were found to significantly reduce seedling mortality and enhance plant biomass of bell pepper. Thus, these experimental findings suggest that a better integrated management of bell pepper blight could be achieved by conducting field trials in major bell pepper- and chilli-cultivated areas of the state. Besides fungicides, different botanicals and commercial botanicals also seem to be promising treatment options. Therefore, the outcome of the present study provides an alternate option of fungicide use in minimizing loss caused by Drechslera bicolor.

Plant growth promoting capability and genetic diversity of bacteria isolated from mud volcano and lime cave of Andaman and Nicobar Islands

Twenty four bacterial strains from four different regions of mud volcano and lime cave were isolated to estimate their diversity, plant growth promoting and biocontrol activities to use them as inoculant strains in the fields. An excellent antagonistic effect against four plant pathogens and plant growth promoting properties such as IAA production, HCN production, phosphate solubilization, siderophore production, starch hydrolysis and hydrolytic enzymes syntheses were identified in OM5 (Pantoea agglomerans) and EM9 (Exiguobacterium sp.) of 24 studied isolates. Seeds (Chili and tomato) inoculation with plant growth promoting strains resulted in increased percentage of seedling emergence, root length and plant weight. Results indicated that co-inoculation gave a more pronounced effects on seedling emergence, secondary root numbers, primary root length and stem length, while inoculation by alone isolate showed a lower effect. Our results suggest that the mixed inocula of OM5 and EM9 strains as biofertilizers could significantly increase the production of food crops in Andaman archipelago by means of sustainable and organic agricultural system.

Effect of different irrigation methods on yield of red hot pepper and plant mortality caused by Phytophthora capsici Leon.

This experiment was conducted in 1999 and 2000 in a field naturally infected by Phytophthora capsici to determine the effects of different irrigation methods, namely, basin (B), closed-end furrow (F), drip (D) and sprinkler (S) irrigation on dry yield of chili pepper (Capsium annuum L. K. Maras Type). Water use efficiency (WUE) and plant mortality were also measured. The averages of total applied water to the B, F, D and S plots for the two years were 937.7 mm, 920.6 mm, 886.5 and 913.4 mm, respectively. Thus, the mean seasonal water use by pepper varied from 1020.7 to 1109.7 mm. The highest water use was measured in B, followed by use for S, D and F methods. The highest mean potential dry yield with 1.58 t ha(-1) was obtained using D method. This was followed by S (1.36 t ha(-1)), B (1.13 t ha(-1)), and F (0.81 t ha(-1)) methods. In terms of plant mortality, crops having B irrigation had the highest (93.9%), followed by lessen amount to the S (3.2%), F (3.1%), and D methods (1.7%). Only the B irrigation method stimulated the development of P. capsici disease. On the other hand, mean WUEs varied between 0.7 and 1.7 kg ha(-1)mnm(-1) for Irrigation methods. WUE for D method was slightly higher than S method, but considerably higher than B and F methods.

Isozyme characterization of Capsicum accessions from the Amazonian Colombian collection / Caracterización por isoenzimas de accesiones de Capsicum pertenecientes a la colección amazónica colombiana

Two hundred and sixty-one accessions of the genus Capsicum were obtained from the Colombian Amazonian germplasm bank at Amazonian Institute of Scientific Research (Sinchi) and were evaluated with five polymorphic enzymatic systems, including esterase (EST), peroxidase (PRX), 6-phosphogluconatedehydrogenase (6-PGDH), aspartate amino transferase (GOT), and malic enzyme (ME). Using a cluster analysis (UPGMA) the genetic variability of these accessions were characterized. Grouping of the species C. baccatum and C. pubescens were observed, while the species C. annuum, C. chinense and C. frutescens did not group independently, a result that has been previously reported in isoenzyme analyses of this genus. Several accessions were deemed of particular interest for future ecological and evolutive studies.

Doscientas sesenta y una accesiones del género Capsicum del banco de germoplasma del Instituto Amazónico de Investigaciones Científicas (Sinchi) se evaluaron a través de cinco sistemas enzimáticos polimórficos: esterasa (EST), peroxidasa (PRX), 6-fosfogluconato deshidrogenasa (6-PGDH), aspartato amino transferasa(GOT) y enzima málica (ME). Se utilizó un análisis de agrupamiento (Upgma) con el fin de determinar la variabilidad genética. Se observó un agrupamiento de las especies C. baccatum y C. pubescens, mientras que las especies C. annuum, C. chinense y C. frutescens no mostraron un agrupamiento independiente, lo cual ya ha sido reportado en estudios por isoenzimas para el género. Varias accesiones mostraron característicasparticulares para estudios ecológicos y evolutivos.

Siderophore production by fluorescent pseudomonads colonizing roots of certain crop plants.

Twelve fluorescent Pseudomonas isolates colonizing roots of four crop plants, chilli, cotton, groundnut and soybean, were examined for extracellular siderophore production in different media under iron deficient conditions. While all the organisms produced siderophores, they varied in the quantity of siderophores produced and in their preference to the medium. The siderophores were invariably hydroxamates (pyoverdine) of trihydroxamate type which formed bidentate ligands with Fe III ions.