Vera Raicevic

Salmonella as an endophytic colonizer of plants - A risk for health safety vegetable production

Contamination of vegetables and fruits is the result of presence of human pathogen bacteria which can contaminate products in any part of production chain. There is an evidence of presence of: Salmonella spp. on the fresh vegetables and Salmonellosis is connected with tomato, sprouts, cantaloupe etc. The goal of this research is transmission of pathogen bacteria from irrigation water to plants and studying/monitoring the ability of the Salmonella spp. to colonize the surface and interior (endophytic colonization) of root at different vegetable species. Transmission of three Salmonella spp. strains from irrigation water to plants, as well as colonization of plants by these bacteria was investigated by using Fluorescence In Situ Hybridization (FISH) in combination with confocal laser scanning microscopy (CLSM). All tested Salmonella spp. strains showed ability to more or less colonize the surface and interior niches of the root, stem and leaf of the investigated plant species. These bacteria also were found in plant cells cytoplasm, although the mechanism of their entrance has not been clarified yet.

Effect of the edaphic factors and metal content in soil on the diversity of Trichoderma spp.

Influence of edaphic factors and metal content on diversity of Trichoderma species at 14 different soil sampling locations, on two depths, was examined. Forty-one Trichoderma isolates from 14 sampling sites were determined as nine species based on their internal transcribed spacer (ITS) sequences. Our results indicate that weakly alkaline soils are rich sources of Trichoderma strains. Also, higher contents of available K and P are connected with higher Trichoderma diversity. Increased metal content in soil was not inhibiting factor for Trichoderma species occurrence. Relationship between these factors was confirmed by locally weighted sequential smoothing (LOESS) nonparametric smoothing analysis. Trichoderma strain (Szeged Microbiology Collection (SZMC) 22669) from soil with concentrations of Cr and Ni above remediation values should be tested for its potential for bioremediation of these metals in polluted soils.

Constructed wetlands as an alternative restoration measure for shallow lakes.

This paper deals with the consequences of cultural eutrophication and unconventional solutions for shallow lake restoration. Cultural eutrophication is the primary problem that affects especially shallow lakes, due to their physical characteristics (e.g. shallow depth, lack of stratification). Palic Lake, a very shallow Pannonian lake, received treated municipal wastewaters coming from the lagoons of a wastewater treatment plant. The sewage discharge mainly increased the nutrient load to the lake in the last decades. The lake sustainability is affected by inappropriate quality of water that flows into the lake, and abundance of deposited sediment. The technology that can provide both improvement of water quality and resolution of the sediment problem is a constructed wetland, which is designed to utilise the natural processes involving wetland vegetation, soil and their associated microbial assemblages to assist in additional water treatment. The technical solution is based on three key aspects: quality and quantity of deposited sediment, enriched by nutrients; effluent quality; desired lake water quality. A designed constructed wetland can accomplish the desired water quality and gradually remediate deposited sediment.

Potential and Constraints of Macrophyte Manipulation for Shallow Lake Management

Palic and Ludas lakes are shallow Pannonian lakes, which have undergone rapid eutrophication. High concentrations of nutrients, along with significantly high values of fecal indicators in water samples, indicate that the Palic-Ludas canal, which connects them, contributes to the pollution of the recipient Lake Ludas, a central part of a special nature reserve. In order to improve water quality in the canal and decrease nutrient load of Lake Ludas, it is suggested to use environmentally friendly solutions, so-called bio-barriers (bio-bridges and biobanks), which will contribute to self-purification efficiency. The given model assumes 10 zones with bio-bridges and 0.4 ha covered by biobanks, using plants common in the area, e.g. Typha spp., Phragmites spp., Juncus spp., Scirpus spp. and Carex spp. The main disadvantage of this technology is occupation of large area; thus, the solution seems to be undersized. It removes 4% TN/year and 8% TP/year of the total amount necessary to achieve good ecological status. Nevertheless, the role of bio-bridges in permanent nutrient removal, through preventing the deposition of organic matter at the bottom sediment and later return of nutrients in water, together with indirect influence through enhancement of biodiversity should not be underestimated.

Listeria monocytogenes – Danger for health safety vegetable production

The microbiologically contaminated vegetables represent a risk for consumers, especially vegetables without thermal processing. It is known that human pathogen bacteria, such as Listeria monocytogenes, could exist on fresh vegetables. The fresh vegetables could become Listeria-contaminated if they come in touch with contaminated soil, manure, irrigation water. The aim of this work was to investigate the presence of Listeria spp. and L. monocytogenes in different kind of vegetables grown in field and greenhouse condition as well as surface and endophytic colonization plant roots of different vegetables species by L. monocytogenes in laboratory conditions. The detection of Listeria spp. and L. monocytogenes in vegetable samples was done using ISO and PCR methods. The investigation of colonization vegetable roots and detection Listeria-cells inside plant root tissue was done using Fluorescence in situ hybridization (FISH) method in combination with confocal laser scanning microscopy (CLSM). The results showed that 25.58% vegetable samples were positive for Listeria spp. and only one sample (carrot) was positive for L. monocytogenes out of 43 samples in total collected from field and greenhouse. The strain L. monocytogenes EGD-E surface and endophytic colonized carrot root in highest degree while strain L. monocytogenes SV4B was the most represented at leafy vegetable plants, such at lettuce (1.68 × 106 cells/mm3 absolutely dry root) and spinach (1.39 × 106 cells/mm3 absolutely dry root) root surface. The cells of L. monocytogenes SV4B were visible as single cells in interior tissue of plant roots (celery and sweet corn roots) as well as in the interior of the plant root cell at sweet corn root. The cells of L. monocytogenes EGD-E bind to the surface of the plant root and they were less commonly found out on root hair. In the inner layers of the root, those bacterial cells were inhabited intercellular spaces mainly as single cells very close to the larval vessels of root. Our results suggest that L. monocytogenes is very good endophytic colonizer of vegetable plant roots.

New insights in dehydration stress behavior of two maize hybrids using advanced distributed reactivity model (DRM). Responses to the impact of 24-epibrassinolide

Proposed distributed reactivity model of dehydration for seedling parts of two various maize hybrids (ZP434, ZP704) was established. Dehydration stresses were induced thermally, which is also accompanied by response of hybrids to heat stress. It was found that an increased value of activation energy counterparts within radicle dehydration of ZP434, with a high concentration of 24-epibrassinolide (24-EBL) at elevated operating temperatures, probably causes activation of diffusion mechanisms in cutin network and may increases likelihood of formation of free volumes, large enough to accommodate diffusing molecule. Many small random effects were detected and can be correlated with micro-disturbing in a space filled with water caused by thermal gradients, increasing capillary phenomena, and which can induce thermo-capillary migration. The influence of seedling content of various sugars and minerals on dehydration was also examined. Estimated distributed reactivity models indicate a dependence of reactivity on structural arrangements, due to present interactions between water molecules and chemical species within the plant.

Potential of pseudomonas aeruginosa environmental isolates for biofilm formation

Biofilm formation is one of the main characteristic of Pseudomonas aeruginosa strains. This ability provide bacteria to survive in different, usually restrictivesss environmental conditions. In the same time, biofilm forming is a risk in a many field of industry, mainly in food industry. It is known that diverse P. aeruginosa strains from various environmental sources have different potention to form biofilms. In this paper it is examinated the potention to form biofilm four isolates of P. aeruginosa and based of this results, tested isolates have classificated into four groups. Biofilm formation tested in microtitar plates during the 24 hours at changed conditions of temperature (37°C and 22°C), pH (6 and 7) and concentration of NaCl (1% and 2%). Obtained results have shown that isolated P. aeruginosa have unsimilar ability to form biofilms. Biomass of formed biofilm was greater at 22°C than at 37°C. Also, acid conditions and higher concentration of salt had no inhibitory effect to biofilm forming process.

Filamentous fungi isolated from grape marc as antagonists of Botrytis cinerea

In this paper we report on the isolation and identification of three filamentous fungi from grape marc, and antifungal effect of their cell-free culture filtrates on the growth of Botrytis cinerea, causal agent of gray mold. Grape marc is a waste material that has been used as soil amendment in sustainable agriculture. Isolates originating from grape marc were identified on the basis of morphological features and internal transcribed spacer rDNA or β-tubulin gene sequencing. The presence of three different species, Penicillium paneum, Penicillium chrysogenum and Aspergillus fumigatus has been detected expressing different effect on the growth of B. cinerea. The effect of crude culture filtrates of selected fungi on B. cinerea growth was tested. Heat sensitivity of the established inhibition effect was examined by autoclaving the crude culture filtrate prior to testing. Additional aim was to determine whether antifungal effect was influenced by previous exposure to B. cinerea in dual liquid cultures. Crude culture filtrate of A. fumigatus K16/2 showed the lowest suppression of B. cinerea growth. A maximal percentage inhibition achieved within the study was 38.2%, 39.8% and 23.8 for crude filtrates of P. paneum K7/1, P. chrysogenum K11/1 and A. fumigatus K16/2, respectively. Presence of B. cinerea in dual liquid culture induced significant increase in antifungal capacity of the culture filtrates in comparison to pure culture filtrates of the chosen isolates. The antifungal activity of all of the isolates’ culture filtrates retained after heat treatment suggesting the presence of some thermostable antifungal metabolites. The results indicate the complexity and specificity of the interaction between filamentous fungi and B. cinerea. Grape marc is a good source for isolation od B. cinerea fungal antagonists and their antifungal metabolites. Specificity of fungal-fungal interactions suggests that further research on the antagonistic mechanisms and factors affecting them should be studied separately for each pair of antagonists. [Projekat Ministarstva nauke Republike Srbije, br. TR 31080 and III 43001, i FP7 Project AREA 316004]

The effect of plant growth promoting rhizobacteria on Datura stramonium L., Abutilon theophrasti Med., Onopordon acanthium L. and Verbascum thapsus L. seed germination.

The effects of several bacterial media [Bacillus licheniformis population 1 (MO1); B. licheniformis population 2 (MO2); B. subtilis (MO3); B. megatherium (MO4); humates (MO5)] on seed germination of Datura stramonium L., Abutilon theophrasti Med., Onopordon acanthium L. and Verbascum thapsus L. were tested. Seeds were germinated in Petri dishes containing solutions with different bacterial media. The highest germination percentage in all treatments was recorded for V. thapsus seeds (100.0%). Different treatments had diverse effects (stimulative or inhibitory) on seed germination of D. stramonium [from 5% (MO1) to 13.3% (MO3), with 10.0 % in H20], A. theophrasti [from 28.3% (MO3) to 65.0% (MO5), with 43.3 % in H20] and O. acanthium [from 10.0% (MO2) to 13.3% (MO1 and MO3), with 6.7% in H20], depending on the type of media and weed species. [Projekat Ministarstva nauke Republike Srbije, br. III46008 i EU project FP7-REGPOT-AREA 316004]

Hygiene in Primary Production

Biological agents, bacteria, viruses and parasites can, directly or indirectly, contaminate food. Similarly chemicals such as veterinary drugs used to combat animal illnesses, mycotoxins particularly aflatoxins, pesticides and environmental contaminants (e.g. dioxins, heavy metals) in animal feeds can also be a source contamination of food. Contamination of agricultural, animal and fish products is the result of the presence of human pathogenic bacteria and/or toxic substances, which can contaminate products in any part of the production chain. Examples are of the presence of a wide range of pathogens such as Salmonella spp., pathogenic Escherichia coli and Shigella , hepatitis A virus on fresh fruits and vegetables, E. coli O157:H7 in meats, Campylobacter spp., Brucella spp. in milk, Vibrio sp. and ciguatera toxin in fish. Thus the importance of good practices at the primary production level to prevent diseases and infections in animals, minimize risk of transmission to humans and/or contamination of food as well as to ensure animal health and welfare. The authors address three main primary production systems and the challenges to reduce the safety threats inherent to each. Good animal farming, fish health and good agricultural practices are described extensively so as to provide a clear picture of the complexity of the food production chains and the many factors that need to be under control to ensure the safety of food products.