Accumulation Of Pathogens Research Articles

Accumulation and Fate of Microorganisms and Microspheres in Biofilms Formed in a Pilot-Scale Water Distribution System

The accumulation and fate of model microbial "pathogens" within a drinking-water distribution system was investigated in naturally grown biofilms formed in a novel pilot-scale water distribution system provided with chlorinated and UV-treated water. Biofilms were exposed to 1-mum hydrophilic and hydrophobic microspheres, Salmonella bacteriophages 28B, and Legionella pneumophila bacteria, and their fate was monitored over a 38-day period. The accumulation of model pathogens was generally independent of the biofilm cell density and was shown to be dependent on particle surface properties, where hydrophilic spheres accumulated to a larger extent than hydrophobic ones. A higher accumulation of culturable legionellae was measured in the chlorinated system compared to the UV-treated system with increasing residence time. The fate of spheres and fluorescence in situ hybridization-positive legionellae was similar and independent of the primary disinfectant applied and water residence time. The more rapid loss of culturable legionellae compared to the fluorescence in situ hybridization-positive legionellae was attributed to a loss in culturability rather than physical desorption. Loss of bacteriophage 28B plaque-forming ability together with erosion may have affected their fate within biofilms in the pilot-scale distribution system. The current study has demonstrated that desorption was one of the primary mechanisms affecting the loss of microspheres, legionellae, and bacteriophage from biofilms within a pilot-scale distribution system as well as disinfection and biological grazing. In general, two primary disinfection regimens (chlorination and UV treatment) were not shown to have a measurable impact on the accumulation and fate of model microbial pathogens within a water distribution system.

Cultivar Decline in Sweetpotato: I. Impact of Micropropagation on Yield, Storage Root Quality, and Virus Incidence in `Beauregard'

Decline in sweetpotato yield and storage root quality has been attributed to the accumulation of viruses, pathogens and mutations. To document the effects of decline on yield and storage root quality, two micropropagated, virus-indexed, greenhouse produced G1 `Beauregard' meristem-tip cultured clones, B94-14 and B94-34, were compared with 1) micropropagated B94-14 and B94-34 clones propagated adventitiously up to five years in the field (G2, G3, G4, G5); and 2) nonmicropropagated, unimproved stock of `Beauregard' seed in field trials during 1997 to 2001. At least three trials were located each year in sweetpotato producing regions in North Carolina. In 2000 and 2001, two trials were monitored weekly for foliar symptoms of Sweet potato feathery mottle virus (SPFMV) and other potyviruses, and virus-indexed for selected viruses using Ipomoea setosa and nitrocellulose enzyme linked immunosorbant assays (NCM-ELISA). Only SPFMV was detected in field samples using NCM-ELISA, but this does not rule out the presence of newly described viruses infecting sweetpotato for which tests were unavailable. Monitoring indicated that all G1 plants became infected with SPFMV by the end of the growing season, and that G2 to G5 plants were probably infected in their initial growing season. G1 plants consistently produced higher total yield, total marketable yield (TMY), U.S. No. 1 root yield and percent No. 1 yield than G2 to G5 plants. G1 plants also produced storage roots with more uniform shapes and better overall appearance than storage roots produced from G2 to G5 plants. Also, G2 to G5 storage roots tended to be longer than G1 storage roots. Rank mean yield and storage root quality measurements of each location were consistent with means averaged over locations per year and suggested a decrease in yield and storage root quality with successive seasons of adventitious propagation. Linear regression analysis used to model yield and storage root quality measurements of seed generations G1 to G5 indicated that total yield, TMY, No. 1 yield, percent No. 1 yield, shape uniformity, and overall appearance decreased gradually, and that length/diameter ratios increased gradually with generation. The rate of decline in No. 1 yield was greater for B94-34 compared to B94-14. Both viruses and mutations of adventitious sprouts arising from storage roots probably contribute to cultivar decline in sweetpotato, but further studies are needed to determine their relative importance. A simple profitability analysis for G1 vs. G2-G4 planting material conducted to facilitate better understanding of the economics of using micropropagated planting material to produce a crop in North Carolina revealed that growers have a potential net return of $2203/ha for G1 plants, $5030/ha for G2 plants, and $4394/ha for G5 plants. Thus, while G1 plants generally produce higher No. 1 yields, a greater monetary return can be achieved using G2 planting materials because of the high costs associated with producing G1 plants. Based on this analysis, the best returns are accrued when growers plant their crop using G2 and/or G3 seed.

Feedback with soil biota contributes to plant rarity and invasiveness in communities.

Understanding the relative abundance of species in plant communities is an unsolved problem. Mechanisms such as competition, resource partitioning, dispersal ability and predation tolerance do not adequately explain relative abundance under field conditions. Recent work suggests that interactions between plants and soil microbes is important. Here I show that such interaction explains a significant proportion of the variance in the relative abundance of species in plant communities. Rare plants exhibited a relative decrease in growth on 'home' soil in which pathogens had had a chance to accumulate, whereas invasive plants benefited from interactions with mycorrhizal fungi. Some plant species accumulate pathogens quickly and maintain low densities as a result of the accumulation of species-specific pathogens, whereas others accumulate species-specific pathogens more slowly and do not experience negative feedback until plant densities reach high levels. These results indicate that plants have different abilities to influence their abundance by changing the structure of their soil communities, and that this is an important regulator of plant community structure.

Mechanisms of Plant Species Coexistence: Roles of Rhizosphere Bacteria and Root Fungal Pathogens

Two independent experiments were conducted to investigate the influence of rhizosphere bacteria on the growth ofAnthoxanthum odoratum andPanicum sphaerocarpon. We tested whether host-specific populations ofBacillus mycoides affected the growth of theirAnthoxanthum andPanicum hosts and whether host-specific differences inBacillus populations modified the strong detrimental effect of the root fungal pathogen, Pythium macrosporum. Our results showed both positive and negative effects ofBacillus inoculation and thatAnthoxanthum andPanicum plants responded differently toBacillus isolates that originated from different host plants.Anthoxanthum grew relatively better with isolates fromPanicum, whilePanicum grew relatively better with isolates fromAnthoxanthum, consistent with a negative feedback. In both experimentsPythium infection was detrimental to plant growth, andPanicum was more negatively affected by inoculation withPythium. Overall,Bacillus ameliorated the pathogenic effect ofPythium. However, there was no evidence that host-specificBacillus populations had different effects on the interaction between these plant species andPythium. Both host-specific differences in rhizosphere bacteria and host-specific accumulation of a fungal pathogen can generate negative feedback between these two plant species.

MECHANISMS OF PLANT SPECIES COEXISTENCE: ROLES OF RHIZOSPHERE BACTERIA AND ROOT FUNGAL PATHOGENS

Two independent experiments were conducted to investigate the influence of rhizosphere bacteria on the growth ofAnthoxanthum odoratum andPanicum sphaerocarpon. We tested whether host-specific populations ofBacillus mycoides affected the growth of theirAnthoxanthum andPanicum hosts and whether host-specific differences inBacillus populations modified the strong detrimental effect of the root fungal pathogen, Pythium macrosporum. Our results showed both positive and negative effects ofBacillus inoculation and thatAnthoxanthum andPanicum plants responded differently toBacillus isolates that originated from different host plants.Anthoxanthum grew relatively better with isolates fromPanicum, whilePanicum grew relatively better with isolates fromAnthoxanthum, consistent with a negative feedback. In both experimentsPythium infection was detrimental to plant growth, andPanicum was more negatively affected by inoculation withPythium. Overall,Bacillus ameliorated the pathogenic effect ofPythium. However, there was no evidence that host-specificBacillus populations had different effects on the interaction between these plant species andPythium. Both host-specific differences in rhizosphere bacteria and host-specific accumulation of a fungal pathogen can generate negative feedback between these two plant species.

Medium-term and long-term in vitro conservation and safe international exchange of yam (Dioscorea spp.) germplasm

Yam edible tubers feed million of peoples in the intertropical area, where they represent 12% of human feeding. However, as a vegetatively propagated crop, yam is seriously affected by an accumulation of pathogens. Establishing in vitro germplasm collection is a process that cleans the plants from all diseases but viruses. It gives a good control on the preservation of the yam genetic resources and facilitates international exchanges of healthy plant material. Two kinds of in vitro germplasm preservation were considered : slow growth condition culture for mid-term preservation, and cryopreservation using the encapsulation/dehydration technique for long-term preservation. Virus eradication was approached by meristem culture and chemo and thermotherapy. Production of virus-free plants was controlled by ELISA. We succeeded in the introduction and maintenance of 20 yam species, under slow growth conditions. Cryopreservation was applied successfully on two edible yam species, Dioscorea . alata L and D. bulbifera L. Virus-free plants were obtained by meristem culture in D. cayenensis-D. rotundata complex and D. praehensilis . Indexation allowed the detection of different virus (poty-, potex-, badna- and cucumovirus), where the most important potyvirus was YMV. Mid-term conservation of yam germplasm is used routinely, and from these conditions a direct acclimatization is possible. On the cryopreservation aspect, experiments are under way to apply the optimized protocol to genotypes which are more representative of the diversity, to insure a routinely use. More work can be conducted now on virus eradication, based on knowledge accumulated on potyvirus diversity, on several tests available for yam indexing (ELISA, rt/PCR, monoclonal antibodies) and on new sanitation techniques.

DEVELOPMENT OF A CLEAN-PLANTING-MATERIAL PRODUCTION SYSTEM ON TROPICAL ROOT AND TUBER CROPS, USING IN VITRO PROPAGATED PLANTS

ISHS International Symposium on Biotechnology of Tropical and Subtropical Species Part 2 DEVELOPMENT OF A CLEAN-PLANTING-MATERIAL PRODUCTION SYSTEM ON TROPICAL ROOT AND TUBER CROPS, USING IN VITRO PROPAGATED PLANTS

Transgenic approaches to microbial disease resistance in crop plants

Recent progress in the genetic dissection of plant disease resistance signaling pathways has opened a number of new avenues towards engineering pathogen resistance in crops. Genes controlling race-specific and broad-spectrum resistance responses have been cloned, and novel induced resistance pathways have been identified in model and crop systems. Advances continue to be made in identification of antifungal proteins with effects inhibitory to either pathogen development or accumulation of associated mycotoxins.

Maintenance of Diversity within Plant Communities: Soil Pathogens as Agents of Negative Feedback

The effect of soil pathogens on plant communities was investigated using four old-field perennial plant species and five isolates of a pathogenic oomycete in the genus Pythium. These Pythium strains were isolated from the roots of two of the plant species, Danthonia spicata and Panicum sphaerocarpon, used in a previous experiment on the consequences of changes in the soil community on plant growth. In this previous experiment, Danthonia and Panicum changed the soil community in a manner that reduced their growth relative to that of a third plant species, Anthoxanthum odoratum. In the current experiments, we found that inoculation with Pythium reduced overall plant mass and root:shoot ratios, but Danthonia and Panicum were more susceptible to the presence of Pythium than the other two plant species, Anthoxanthum and Plantago lanceolata. In addition, Pythium accumulates at different rates on different plant species, with a greater than tenfold higher population observed in association with Panicum compared to Anthoxanthum. The results of these experiments suggest that the accumulation of species-specific soil pathogens could account for the previous observation of negative feedback on plant growth through changes in the soil community. As negative feedback may act to maintain plant species diversity within a community, these results suggest that soil pathogens may themselves contribute to the maintenance of plant species diversity.

MAINTENANCE OF DIVERSITY WITHIN PLANT COMMUNITIES: SOIL PATHOGENS AS AGENTS OF NEGATIVE FEEDBACK

The effect of soil pathogens on plant communities was investigated using four old-field perennial plant species and five isolates of a pathogenic oomycete in the genus Pythium. These Pythium strains were isolated from the roots of two of the plant species, Danthonia spicata and Panicum sphaerocarpon, used in a previous experiment on the consequences of changes in the soil community on plant growth. In this previous experiment, Danthonia and Panicum changed the soil community in a manner that reduced their growth relative to that of a third plant species, Anthoxanthum odoratum. In the current experiments, we found that inoculation with Pythium reduced overall plant mass and root:shoot ratios, but Danthonia and Panicum were more susceptible to the presence of Pythium than the other two plant species, Anthoxanthum and Plantago lanceolata. In addition, Pythium accumulates at different rates on different plant species, with a greater than tenfold higher population observed in association with Panicum compared to Anthoxanthum. The results of these experiments suggest that the accumulation of species-specific soil pathogens could account for the previous observation of negative feedback on plant growth through changes in the soil community. As negative feedback may act to maintain plant species diversity within a community, these results suggest that soil pathogens may themselves contribute to the maintenance of plant species diversity.

Bacterial Pathogens and Indicators in Poultry Litter during Re-Utilization

A study of broiler litter re-utilization potential was conducted with a goal of determining if a coarse litter fraction could be safely re-utilized as a supplement for wood shavings bedding without significant pathogen accumulation. Pathogenic and indicator bacteria were monitored in three litter types (coarse fractions of fresh or stored litter supplemented with wood shavings, or wood shavings alone) during a 40-day growth period in broiler house pens. Initial microbial concentrations were higher in fresh litter than in stored litter or wood shavings. Significant increases in microbial concentrations occurred during 40 days of re-utilization in fresh/stored/shavings litter. No consistent significant differences were found among concentrations of microorganisms in fresh/stored/shavings litter during re-utilization.

Expression and localization of two in planta induced extracellular proteins of the fungal tomato pathogen Cladosporium fulvum.

Expression of two in planta induced genes of the biotrophic fungal tomato pathogen Cladosporium fulvum and accumulation of their products, extracellular proteins (ECPs), were studied in time and space during pathogenesis. Immunogold localization revealed that proteins ECP1 and ECP2 accumulated abundantly in extracellular material in the vicinity of fungal and host cell walls. Expression of the genes encoding ECP1 and ECP2 was studied in transformants carrying the reporter gene Gus fused to promoter sequences of the ecp genes. In germinated conidia on the leaf surface no expression of gene ecp1 and only low expression of gene ecp2 could be detected. Expression of both ecp1 and ecp2 was strongly induced during colonization of the intercellular space between tomato mesophyll cells. The highest expression was observed in hyphae growing near vascular tissue. Expression levels were low in newly formed conidia on leaves. Possible functions of ECP1 and ECP2 for C. fulvum during pathogenesis are discussed.

Hot-water treatment of liatris tubers

Liatris ( Liatris spicata) is propagated commercially via tubers. As a result, accumulation of tuberborne pathogens has become a significant production limitation. To overcome this problem, the use of post-harvest hot-water treatment (HWT) of tubers was examined. While verticillium ( Verticillium dahlia) spores died after a 40 min HWT at 49°C, tubers were injured only after being exposed to a HWT of 53°C. This indicates that a 49°C HWT for 40 min is a practical way of destroying verticillium spores in liatris tubers. However, since the verticillium spores are internal, the heat treatment that is sufficient to be lethal to the spores will also damage the peripherally located buds. Tuber injury was accompanied by enhanced electrolyte leakage and a decline in membrane-protein thiols. Our results point to a possible causal relationship between tuber survival, membrane integrity and protein thiol content.

Occurrence of middle ear pathogens in the nasopharynx of young individuals:A quantitative study in four age groups

Colonization of middle ear pathogens (S. pneumoniae, H. influenzae and B. catarrhalis), potential pathogens (S. aureus and coagulase-negative staphylococci) and non-pathogens was determined quantitatively on the posterior wall of the nasopharynx (NPH) of children (four age groups: under 2 years, 2-5 years, 6-10 years and 11-15 years). None of the 90 individuals examined was suffering at the time of bacterial sampling from acute otitis media (AOM), sinusitis, or tonsillitis. All individuals under 2 years of age harboured middle ear pathogens in the NPH, but only 40% of the individuals of the oldest age group (p less than 0.001). Furthermore, in the youngest group, 57% of the cases had pathogens in the NPH, which completely dominated the bacterial flora, i.e. constituted more than 90% of the total bacterial count when calculated as CFU/cm2. The corresponding count in the oldest age group was only 20% (p less than 0.01). One important reason for the high incidence of AOM among young children in particular seems to be the noticeable accumulation of middle ear pathogens in huge quantities in the NPH in this age group.

Die Wirkung einiger Biozide auf die Bodenmüdigkeit bei Apfel und auf die Mikroflora müder Böden

Summary Many plant species being cultivated one after another immediately or too quickly show growth and yield reductions which are called replant damages. Besides the accumulation of known pathogens still unknown causes are made responsible for this phenomenon. Only the last are to adjoin to the term soil sickness. Among the replant damages with apples soil sickness cuts a special figure. It is characterized by a high peristence in the soil even after a short-term apple cultivation. Therefore it cannot be overcome by realizable cultivation stops. From own investigations the hypothesis was derived that soil sickness is caused by soil actinomycetes. These organisms penetrate into the fibrous roots, colonize and damage them so that the roots die off. This process results in an enrichment of the actinomycetes in the soil. Investigations about the suitability of different biocides for the control of soil sickness led to the result that some of them posess marked actinomycidic properties when added to microbial culture media. These cannot be proved when they were added to soil. In accordance with this observation there is to observe no activity against soil sickness. Other biocides with pronounced actinomycidic properties in agar media and a low activity in soil don't influence the growth of apple seedlings in sick soil too. Only biocides with high actinomycidic activity in soil are able to remove the effects of soil sickness. The results obtained are discussed in connection with the hypothesis about the cause of soil sickness in apple.

Accumulation of Escherichia coli by the Northern quahaug.

The uptake of Escherichia coli by the quahaug, Mercenaria mercenaria, was studied to obtain an insight into the environmental parameters significant to the accumulation of bacterial pathogens by shellfish growing in polluted waters and into the kinetics of the uptake process. Experimental uptake was achieved by placing the animals in a flowing water system in which the contamination level of the water and its temperature and salinity could be controlled. Data from periodic assays of individual animals suggested that accumulation of the bacteria by the quahaug proceeds to an equilibrium level which is a function of E. coli content of the water and its overall particulate matter. Accumulation takes place in the digestive gland and, to a lesser extent, in the siphon of the animal.

Accumulation of Escherichia coli by the Northern Quahaug 1

The uptake of Escherichia coli by the quahaug, Mercenaria mercenaria, was studied to obtain an insight into the environmental parameters significant to the accumulation of bacterial pathogens by shellfish growing in polluted waters and into the kinetics of the uptake process. Experimental uptake was achieved by placing the animals in a flowing water system in which the contamination level of the water and its temperature and salinity could be controlled. Data from periodic assays of individual animals suggested that accumulation of the bacteria by the quahaug proceeds to an equilibrium level which is a function of E. coli content of the water and its overall particulate matter. Accumulation takes place in the digestive gland and, to a lesser extent, in the siphon of the animal.

Incidence of Rhizoctonia in a cultivated and a fallow soil in Hong Kong.

THE arable land available in Hong Kong is very limited and farming is so intensive that the annual production of 8–9 vegetable crops, often on the same land, is common. For many reasons, especially from an accumulation of soil-borne pathogens, this might be expected to have a deleterious effect on the soil.