Probiotic bacteria have been investigated in the prevention and treatment of various diseases and allergies. The current study was undertaken to determine the effect of eight probiotic Lactobacillus species against bacterial human skin pathogens using several techniques. Antimicrobial activity of lactobacilli against Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa and Propionibacterium acnes was evaluated using lactobacilli broth cultures (BCB) and cell free supernatant (CFS). Antimicrobial activity was significantly greater with BCB compared with CFS especially for Lactobacillus plantarum and Lactobacillus acidophilus. Lactobacilli and pathogen aggregation, biofilm formation and adhesion to keratin were assessed. L. casei and L. plantarum were selected for further study as they showed the greatest co-aggregation (18.02 ± 1.34% with L. casei and 14.92 ± 1.45% with L. plantarum) with the pathogens (16.63 ± 1.65% with S. aureus 3761 and 14.58 ± 1.68% with P. aeruginosa) and prevention of biofilm formation by the pathogens. The antimicrobial activity of human beta defensin-2 (hBD-2) alone or with L. plantarum against pathogens was assessed. The results with hBD-2 showed that hBD-2 (10 μg / ml for 5 h) and L. plantarum together were significantly more inhibitory against S. aureus than hBD-2 alone. The presence of NaCl reduced the effectiveness of hBD-2 alone and with L. plantarum. In the presence of L. plantarum, inactivation of mprF and dlt genes led to increased binding of hBD-2 by the bacterial cell wall, and then inhibition growth of bacterial cell wall. Studies investigated the effect of exposure of methicillin resistant Staphylococcus aureus (MRSA) to the supernatant of L. plantarum the susceptibility of MRSA to β-lactams. MRSA became sensitive to β-lactams when treated with culture supernatant of L. plantarum. Gene expression studies demonstrated that the mecR1-mecI-mecA-PBP2 signalling pathway was impeded by exposure to culture supernatant of L. plantarum and β-lactams. The studies reported here demonstrate a possible alternative approach to dealing with skin pathogens, which may have clinical implications especially with regard to MRSA infections, and continued research is advised.

When foodstuffs are subject to microbial infection a range of volatile organic compounds (VOCs) are released which can be indicative of both the type and severity of the infection. The bacterium Erwinia carotovora, the primary cause of soft rot, is a major problem in the bulk storage of potato tubers. A number of classes of VOCs have been identified above E. carotovora infected potato tubers, but no disease specific marker has been identified. A number of studies have concluded that the best marker of E. carotovora infection is a substantial increase in the concentration of VOCs in the headspace above the tubers. Chemical sensors which are sensitive to low levels of the VOCs identified in the headspace above infected tubers have been developed. The aim was to use these sensors as the basis of a system for the early detection of soft rot in stored potato tubers. The sensors developed fall into two main categories: those which required heating to elevated temperatures, and those which were operated at ambient temperatures. The sensors operated at ambient temperatures included composites of tin dioxide and chemically prepared polypyrroles. The composites exhibited a high sensitivity to a range of organic vapours (1-100 vpm) and were more sensitive than either tin dioxide or polypyrrole at room temperature. Composites of chemically prepared polypyrroles with various thermoplastics were fabricated and were found to exhibit a high sensitivity to a range of volatile amines. Further studies incorporated chemically prepared polypyrroles into a printing ink vehicle, and sensors constructed from these films displayed good sensitivity, high stability and high mechanical strength. The sensors operated at elevated temperatures included a range of evaporated tin oxide films doped with Pt, CuO and ZnO, plus a range of thick film sensors based on tin dioxide, zinc oxide and mixtures of the two materials. The thick film sensors exhibited the highest sensitivity to the vapours of interest and also gave superior reproducibility of fabrication when compared to the sensors based on evaporated thin films. A synergistic effect appeared to be in operation where tin dioxide and zinc oxide were mixed, with sensors incorporating composites of the two materials exhibiting higher sensitivities than either tin dioxide or zinc oxide alone. A GC-MS study to elucidate the surface reactions occuring on exposure to the vapour, suggested that the synergistic effect was in part due to differences in the catalytic activities/pathways of the two materials. A prototype device was produced based on two evaporated tin dioxide film sensors and one thick film tin dioxidelzinc oxide (50/50 mlm) sensor. The device was tested to various quantities of sound tubers with an infected tuber added. The prototype device was capable of detecting one infected tuber amongst 100kg of sound tubers in a simulated storage crate.

No description available.

No description available.

This work examines the ecological, social and genetic factors that predispose amphibians to infection. In the last 30 years many amphibian populations have declined due to infectious disease, although few researchers have studied the factors involved in mediating amphibian infection. My research is designed to explore some of these factors. I first examined the effects of crowding, kin composition (the relatedness of individuals in a group), and habitat complexity on the growth and survival of Xenopus laevis tadpoles exposed to the bacterial pathogen Aeromonas hydrophila. In tadpoles, stress, and in particular corticosterone, a hormone associated with stress, is known to inhibit growth. Crowding, kin composition, and habitat complexity have all been linked to tadpole growth. As corticosterone exposure is also linked to reduced immune function, I examined how these ecological factors influence tadpoles' disease resistance. Tadpoles exposed to the bacterium were significantly smaller and more likely to die than control tadpoles. Tadpoles reared only with siblings (pure sibship groups) were larger, less variable in size, and had lower mortality rates than tadpoles reared in mixed sibship groups. The size difference between pure and mixed sibship groups was greatest when they were exposed to the pathogen. Habitat complexity reduced size variation within tanks but did not affect mean tadpole size. Mixed kinship composition and high tadpole density can increase competition, reduce growth, and increase disease susceptibility. These results indicate that growth was inhibited by pathogen exposure but kin association may ameliorate this effect. The Major Histocompatibility Complex (MHC) is an integral part of the vertebrate adaptive immune system. To determine the importance of the MHC in conferring disease resistance in amphibians, I challenged X. laevis tadpoles, bearing different combinations of four MHC haplotypes (f, g, j, and r), with A. hydrophila in two experiments. Exposure to A. hydrophila affected the growth and survival of these tadpoles and that the MHC moderated these effects. Tadpoles with two MHC haplotypes (r and g) were susceptible to this pathogen and tadpoles with the other two haplotypes (f and j) were resistant. Heterozygous tadpoles with both susceptible and resistant haplotypes were always intermediate to either homozygotes in size and survival. These results demonstrate that MHC genotype plays a major role in determining the impact of bacterial pathogens on the growth and survival of X. laevis tadpoles. To test whether the effect of exposure to pathogens differs according to the similarity of the hosts I challenged tadpoles with natural levels of the microorganisms associated with different MHC genotypes by exposing the tadpoles to water preconditioned by adults of different MHC genotypes. If the pathogens are adapted to the MHC genotype of their hosts, tadpoles exposed to water from adults with which they shared MHC haplotypes would be more susceptible than those exposed to water from MHC-dissimilar adults. Alternatively, if the hosts are adapted to their pathogens tadpoles may be more resistant to pathogens from MHC-similar frogs than those from MHC-dissimilar frogs. I found that tadpoles exposed to water from MHC-dissimilar animals developed faster, but without increased growth, and were more likely to die than those exposed to water from MHC-similar animals. Furthermore, there was an optimal difference between the tadpoles’ and the donors’ MHC where tadpoles were sufficiently different to the donor to defend against its locally adapted pathogens, and sufficiently similar to not be exposed to especially virulent foreign pathogens. Finally, I present an inventory of bacteria found in the gut and skin (nonsystemic sites) and heart, muscle, and abdominal cavity (systemic sites) of captive frogs. I found several species of bacteria previously identified as amphibian pathogens and many bacteria in systemic sites that have not been considered pathogenic to amphibians. None of the frogs tested positive for the amphibian chytrid fungus, Batrachochytrium dendrobatidis. I discuss the potential importance of these species of bacteria as amphibian pathogens and as protective probiotics, using New Zealand frogs as a case study. In its sum, this work describes some of the factors that can affect amphibians’ ability to resist disease. I show that the genetic constitution of an individual, specifically in terms of the MHC, affects the impact of a disease, and so too does its social and ecological conditions, including the level of crowding, the kinship of its groupmates and the specific microbial challenges of its immediate environment. I also show that many of the factors linked to tadpole growth and development that are well described in other amphibians also affect Xenopus tadpoles.

26 pp. / Geographically, Arizona can be divided roughly into four areas, southwest, central, southeast, and northern. These regions correspond with four climatic zones, allowing a large and diverse number of plants to be grown for landscaping purposes. But, interestingly, in this desert environment many of the parasitic diseases in landscape plants are caused by a limited number of plant pathogens. This publication discusses some of those diseases that are sufficiently important to the urban plants in all areas Arizona.

Downy mildew of broccoli, cauliflower and cabbage is caused by the fungus Peronospora parasitica. Cool moist environmental conditions favor the development of downy mildew on these crops. Several potential new fungicides were evaluated for control of this disease on broccoli in 2001. The final severity of downy mildew in this trial was moderate. Significant reduction in disease severity compared to nontreated plants was achieved by application of available compounds such as Aliette, Bravo, Maneb, Serenade and Trilogy. The nonregistered chemistries Acrobat, Actigard, Curzate, Flint, BAS 500, DPX-KP481 and Quadris also were active against broccoli downy mildew. Actigard was the superior treatment in this trial, as plants treated with this compound were almost free of disease. The future registration and subsequent availability of one or more of these new chemistries for broccoli and related crops could enhance the overall level of disease control as well as help minimize the risk of development of resistance to fungicides used to manage downy mildew.

A fungicide trial was established at The University of Arizona Marana Agricultural Center in April 2000 to evaluate rotation and timing of application for several fungicides used for control of powdery mildew on cantaloupe. Treatments included seven registered fungicides: azoxystrobin, micronized sulfur, neem extract, potassium bicarbonate, benomyl, thiophanate methyl and trifloxystrobin. Different rotations and timing of application of these fungicides were applied either before or immediately after initial signs of powdery mildew infection and up to three times thereafter depending on rotation scheme. By the second application, disease severity was mild but increased rapidly, and it was severe by the time of the last application. Powdery mildew was controlled to some degree on the upper leaf surface by all treatments. However, efficacy was more variable on the lower leaf surface and was reduced when applications were made only at dates 1 and 2. Results show the increased efficacy of fungicides with systemic or trans-laminar activity and the possibilities of rotations with contact fungicides for resistance management.

Sclerotinia leaf drop in Arizona is caused by two soil-borne fungi, Sclerotinia minor and S. sclerotiorum. Moist soil and moderate temperature favor this disease. Some new products in development were evaluated for control of leaf drop on lettuce during the winter vegetable growing season of 2000-2001. Sclerotia of each pathogen were applied to plots after thinning and just before the first of two applications of test compounds. A high level of disease control in the S. minor plots occurred with an appropriate concentration of Plantpro 45, Fluazinam, Contans, BAS 510, BAS 510+BAS 500, Medallion and Serenade. The same products (except Serenade) at an appropriate rate significantly reduced the amount of leaf drop caused by S. sclerotiorum. Elevate did not significantly reduce disease caused by either pathogen. Two of the products tested, Serenade and Contans, are biological control materials. Continued demonstration of efficacy by one or both of these products may provide the opportunity to utilize biological control agents to manage Sclerotinia leaf drop.

Powdery mildew can occur on melons annually in Arizona. Sphaerotheca fuliginea is the plant pathogenic fungus that causes powdery mildew of cucurbits, such as cantaloupe, honeydew, watermelon, cucumber and squash. When environmental conditions are favorable, disease incidence and severity can reach economically significant levels. Development of powdery mildew on melons is favored by moderate temperatures and relative humidity, succulent plant growth and reduced light intensity brought about by a dense plant canopy. Potential new fungicides were evaluated and compared to existing chemicals for control of powdery mildew of cantaloupe in a field trial conducted during the spring of 2000 at the Yuma Agricultural Center A moderately high level of disease had developed by crop maturity (June 22) on nontreated plants. All treatments significantly reduced the level of powdery mildew on both sides of leaves, compared to nontreated plants. The best treatments among those tested with respect to disease control on the underside of leaves, where disease is more difficult to control than on the tops of leaves, included Actigard, Armicarb+Quadris, BAS 500, Benlate+Microthiol, Flint, Flint+Trilogy, Microthiol, Quadris+Actigard, Quadris+Benlate, Quinoxyfen, Nova, Nova+KHHUBF, Topsin, Topsin+Trilogy, Benlate, Benlate+Trilogy, Folicur, Quadris and Topsin+Microthiol. The potential availability of new chemistries for management of powdery mildew of cantaloupe and other cucurbits could help improve overall control of powdery mildew as well as facilitate the development of fungicide resistance management strategies, which strive to minimize the risk of resistance development by the pathogen to these compounds.