scholarly journals Epidemiological Studies of Pan-Azole Resistant Aspergillus fumigatus Populations Sampled during Tulip Cultivation Show Clonal Expansion with Acquisition of Multi-Fungicide Resistance as Potential Driver

2021 ◽  
Vol 9 (11) ◽  
pp. 2379
Author(s):  
Bart A. Fraaije ◽  
Sarah L. Atkins ◽  
Ricardo F. Santos ◽  
Steven J. Hanley ◽  
Jonathan S. West ◽  
...  
Keyword(s):  
Aspergillus Fumigatus ◽  
Fungicide Resistance ◽  
Acquired Resistance ◽  
Epidemiological Studies ◽  
Sensitivity Testing ◽  
Tulip Bulb ◽  
Fungicide Sensitivity ◽  
Plant Disease Control ◽  
Population Comparisons ◽  
Benzimidazole Carbamates

Pan-azole resistant isolates are found in clinical and environmental Aspergillus fumigatus (Af) populations. Azole resistance can evolve in both settings, with Af directly targeted by antifungals in patients and, in the environment, Af unintendedly exposed to fungicides used for material preservation and plant disease control. Resistance to non-azole fungicides, including methyl benzimidazole carbamates (MBCs), quinone outside inhibitors (QoIs) and succinate dehydrogenase inhibitors (SDHIs), has recently been reported. These fungicide groups are not used in medicine but can play an important role in the further spread of pan-azole resistant genotypes. We investigated the multi-fungicide resistance status and the genetic diversity of Af populations sampled from tulip field soils, tulip peel waste and flower compost heaps using fungicide sensitivity testing and a range of genotyping tools, including STRAf typing and sequencing of fungicide resistant alleles. Two major clones were present in the tulip bulb population. Comparisons with clinical isolates and literature data revealed that several common clonal lineages of TR34/L98H and TR46/Y121F/T289A strains that have expanded successfully in the environment have also acquired resistance to MBC, QoI and/or SDHI fungicides. Strains carrying multiple fungicide resistant alleles have a competitive advantage in environments where residues of multiple fungicides belonging to different modes of action are present.

scholarly journals Polymyxins and Bacterial Membranes: A Review of Antibacterial Activity and Mechanisms of Resistance

Membranes ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 181 ◽  
Author(s):  
Carole Ayoub Moubareck
Keyword(s):  
Current Knowledge ◽  
Acquired Resistance ◽  
Epidemiological Studies ◽  
Multidrug Resistant ◽  
Gram Negative ◽  
Bacterial Membranes ◽  
Antibiotic Development ◽  
Outer Membranes ◽  
Initial Discovery ◽  
Clinical Interest

Following their initial discovery in the 1940s, polymyxin antibiotics fell into disfavor due to their potential clinical toxicity, especially nephrotoxicity. However, the dry antibiotic development pipeline, together with the rising global prevalence of infections caused by multidrug-resistant (MDR) Gram-negative bacteria have both rejuvenated clinical interest in these polypeptide antibiotics. Parallel to the revival of their use, investigations into the mechanisms of action and resistance to polymyxins have intensified. With an initial known effect on biological membranes, research has uncovered the detailed molecular and chemical interactions that polymyxins have with Gram-negative outer membranes and lipopolysaccharide structure. In addition, genetic and epidemiological studies have revealed the basis of resistance to these agents. Nowadays, resistance to polymyxins in MDR Gram-negative pathogens is well elucidated, with chromosomal as well as plasmid-encoded, transferrable pathways. The aims of the current review are to highlight the important chemical, microbiological, and pharmacological properties of polymyxins, to discuss their mechanistic effects on bacterial membranes, and to revise the current knowledge about Gram-negative acquired resistance to these agents. Finally, recent research, directed towards new perspectives for improving these old agents utilized in the 21st century, to combat drug-resistant pathogens, is summarized.

scholarly journals Relationship Between Fungicide Sensitivity and Control of Gummy Stem Blight of Watermelon Under Field Conditions

Plant Disease ◽  
2012 ◽  
Vol 96 (12) ◽  
pp. 1780-1784 ◽  
Author(s):  
A. Thomas ◽  
D. B. Langston ◽  
H. F. Sanders ◽  
K. L. Stevenson
Keyword(s):  
Fungicide Resistance ◽  
Field Experiments ◽  
In Vitro Assays ◽  
Didymella Bryoniae ◽  
Fungicide Sensitivity ◽  
Thiophanate Methyl ◽  
Stem Blight ◽  
Gummy Stem Blight ◽  
And Control

Gummy stem blight (GSB), caused by the fungus Didymella bryoniae, is the most destructive disease of watermelon and is managed primarily with fungicides. D. bryoniae has developed resistance to many fungicides that were once very effective, including azoxystrobin, boscalid, and thiophanate-methyl. Field experiments were conducted in Tifton (TN) and Reidsville (RV), GA in 2009 and 2010 to establish a relationship between frequency of resistance to a fungicide based on in vitro assays and its efficacy in the management of GSB. Frequency of resistance to boscalid, thiophanate-methyl, and azoxystrobin was >0.80 in isolates collected from nontreated plots in both locations and years. All isolates collected after six applications of boscalid, thiophanate-methyl, or azoxystrobin were resistant to the respective fungicide. All isolates collected from treated and nontreated plots were sensitive to tebuconazole and difenoconazole. GSB severity was assessed on a weekly basis from 63 days after planting. GSB severity in plots treated with boscalid, thiophanate-methyl, or azoxystrobin was not significantly different from that in the nontreated plots (39%, TN-2009; 45%, TN-2010; and 16%, RV-2010). GSB severity in tebuconazole-treated plots (27%, TN-2009; 14%, TN-2010; and 4%, RV-2010) was significantly lower than all other treatments and the nontreated control. There was a consistent negative association between frequency of fungicide resistance and disease control in the field. Thus, knowledge of the frequency of fungicide resistance in the pathogen population will be helpful in selecting the most effective fungicides for the management of GSB in watermelon fields.

scholarly journals Azole-Resistant Aspergillus fumigatus Harboring the TR34/L98H Mutation: First Report in Portugal in Environmental Samples

2020 ◽  
Vol 9 (1) ◽  
pp. 57
Author(s):  
Paulo Gonçalves ◽  
Aryse Melo ◽  
Marta Dias ◽  
Beatriz Almeida ◽  
Liliana Aranha Caetano ◽  
...  
Keyword(s):  
Aspergillus Fumigatus ◽  
Positive Impact ◽  
Treatment Success ◽  
Acquired Resistance ◽  
Sensu Stricto ◽  
Indoor Environments ◽  
Intrinsic Resistance ◽  
Healthcare Facilities ◽  
Increased Risk ◽  
Respiratory Protective Devices

Introduction: The frequency in detection of azole-resistant Aspergillus fumigatus isolates has increased since 2010. In Portugal, the section Fumigati is one of the most frequent, and resistant strains to have been found in clinical and environmental contexts. Although several cryptic species within the Fumigati section show intrinsic resistance to azoles, one factor driving (acquired) resistance is selective pressure deriving from the extensive use of azoles. This is particularly problematic in occupational environments where high fungal loads are expected, and where there is an increased risk of human exposure and infection, with impact on treatment success and disease outcome. The mechanisms of resistance are diverse, but mainly associated with mutations in the cyp51A gene. Despite TR34/L98H being the most frequent mutation described, it has only been detected in clinical specimens in Portugal. Methods: We analyzed 99 A. fumigatus isolates from indoor environments (healthcare facilities, spas, one dairy and one waste sorting unit) collected from January 2018 to February 2019 in different regions of Portugal. Isolates were screened for resistance to itraconazole, voriconazole and posaconazole by culture, and resistance was confirmed by broth microdilution. Sequencing of the cyp51A gene and its promoter was performed to detect mutations associated with resistance. Results: Overall, 8.1% of isolates were able to grow in the presence of at least one azole, and 3% (isolated from the air in a dairy and from filtering respiratory protective devices in a waste sorting industry) were pan-azole-resistant, bearing the TR34/L98H mutation. Conclusion: For the first time in Portugal, we report environmental isolates bearing the TR34/L98H mutation, isolated from occupational environments. Environmental surveillance of the emergence of azole-resistant A. fumigatus sensu stricto strains is needed, to ensure proper and timely implementation of control policies that may have a positive impact on public and occupational health.

scholarly journals Determination of Natural Resistance Frequencies in Penicillium digitatum Using a New Air-Sampling Method and Characterization of Fludioxonil- and Pyrimethanil-Resistant Isolates

2010 ◽  
Vol 100 (8) ◽  
pp. 738-746 ◽  
Author(s):  
L. Kanetis ◽  
H. Förster ◽  
J. E. Adaskaveg
Keyword(s):  
Concentration Gradient ◽  
Fungicide Resistance ◽  
Sampling Method ◽  
Management Strategies ◽  
Air Sampling ◽  
Penicillium Digitatum ◽  
Natural Resistance ◽  
Fungicide Sensitivity ◽  
Laboratory Selection ◽  
Wide Range

Fungicide resistance was identified in natural populations of Penicillium digitatum, the causal agent of green mold of citrus, to two of three new postharvest fungicides before their commercial use. Using a new air-sampling method where large populations of the pathogen in citrus packinghouses were exposed to agar plates with a continuous, wide-range fungicide concentration gradient, isolates with reduced sensitivity to fludioxonil or pyrimethanil were obtained. Resistance frequencies to fludioxonil and pyrimethanil were calculated as 9.5 × 10–7 to 1.5 × 10–5 and 7.3 × 10–6 to 6.2 × 10–5, respectively. No isolates resistant to azoxystrobin were detected. Isolates with reduced sensitivity to fludioxonil or pyrimethanil were also obtained in laboratory selection studies, where high concentrations of conidial mixtures of isolates sensitive to the three fungicides were plated onto agar amended with each fungicide at 10 μg/ml. Isolates obtained from fludioxonil selection plates in laboratory and packinghouse experiments were placed into two categories based on mycelial growth: moderately resistant isolates had 50% effective concentration (EC50) values of 0.1 to 0.82 μg/ml and highly resistant isolates had EC50 values > 1.5 μg/ml. Isolates resistant to pyrimethanil all had EC50 values >8 μg/ml. Representative isolates of the two categories with reduced sensitivity to fludioxonil varied widely in their virulence and sporulation capacity as measured by the incidence of decay and degree of sporulation on inoculated fruit, respectively, whereas pyrimethanil-resistant isolates were mostly similar to the wild-type isolate. Fungicide sensitivity characteristics for isolates from fludioxonil and pyrimethanil selection plates remained stable after passages on nonamended agar, and disease could not be controlled after treatment with the respective fungicides. Types of fungicide resistance were visualized on thiabendazole- (TBZ) and imazalil-amended selection plates that were exposed in packinghouses where resistance to these fungicides was known to occur. The qualitative, single-site resistance to the benzimidazole TBZ was visualized by two distinct subpopulations in regard to fungicide sensitivity, whereas the quantitative, multi-site resistance to the demethylation inhibitor imazalil was apparent as a continuous density gradient of colonies along the fungicide concentration gradient. Types of resistance could not be assigned to fludioxonil or pyrimethanil because a limited number of resistant colonies was obtained on each plate. Thus, with this new method, we were able to estimate fungicide resistance frequencies as well as characterize and visualize types of resistance within populations of a fungal species. This information will be used to design resistance management strategies for previous and newly registered postharvest fungicides of citrus.

Sensitivity of Australian isolates of Plasmopara viticola to acylanaline fungicides

1987 ◽  
Vol 27 (4) ◽  
pp. 601
Author(s):  
T Wicks ◽  
TC Lee ◽  
J Overton
Keyword(s):  
Phosphorous Acid ◽  
Plasmopara Viticola ◽  
Leaf Disk ◽  
Sensitivity Testing ◽  
Fungicide Sensitivity ◽  
Floating Leaf

A floating leaf disk technique was used to test the sensitivity of Australian isolates of Plasmopara viticola to 4 acylanaline fungicides, phosethyl-A1 and phosphorous acid. Sporulation of all 15 isolates was completely inhibited by 1 mg/L of metalaxyl. Benalaxyl, oxadixyl and ofurace at 10 mg/L and phosethyl-A1 and phosphorous acid at 100 mg/L also completely inhibited sporulation of each of the isolates tested for each fungicide. These results indicate that acylanaline insensitive isolates of P. viticola are either not present or are not widely distributed in grape growing areas of Australia. Cultures of selected P. viticola isolates have been established on tissue-cultured grapevines. Sporangia from these cultures can be used as standards for future fungicide sensitivity testing.

scholarly journals The Multi-Fungicide Resistance Status of Aspergillus fumigatus Populations in Arable Soils and the Wider European Environment

2020 ◽  
Vol 11 ◽  
Author(s):  
Bart Fraaije ◽  
Sarah Atkins ◽  
Steve Hanley ◽  
Andy Macdonald ◽  
John Lucas
Keyword(s):  
Aspergillus Fumigatus ◽  
Crop Production ◽  
Agricultural Soils ◽  
Acquired Resistance ◽  
Surface Protein ◽  
Health Concern ◽  
Azole Resistance ◽  
Arable Soils ◽  
Resistance Development ◽  
Resistance Evolution

The evolution and spread of pan-azole resistance alleles in clinical and environmental isolates of Aspergillus fumigatus is a global human health concern. The identification of hotspots for azole resistance development in the wider environment can inform optimal measures to counteract further spread by minimizing exposure to azole fungicides and reducing inoculum build-up and pathogen dispersal. We investigated the fungicide sensitivity status of soil populations sampled from arable crops and the wider environment and compared these with urban airborne populations. Low levels of azole resistance were observed for isolates carrying the CYP51A variant F46Y/M172V/E427K, all belonging to a cluster of related cell surface protein (CSP) types which included t07, t08, t13, t15, t19, and t02B, a new allele. High levels of resistance were found in soil isolates carrying CYP51A variants TR34/L98H and TR46/Y121F/T289A, all belonging to CSP types t01, t02, t04B, or t11. TR46/Y121F/M172V/T289A/G448S (CSP t01) and TR46/Y121F/T289A/S363P/I364V/G448S (CSP t01), a new haplotype associated with high levels of resistance, were isolated from Dutch urban air samples, indicating azole resistance evolution is ongoing. Based on low numbers of pan-azole resistant isolates and lack of new genotypes in soils of fungicide-treated commercial and experimental wheat crops, we consider arable crop production as a coldspot for azole resistance development, in contrast to previously reported flower bulb waste heaps. This study also shows that, in addition to azole resistance, several lineages of A. fumigatus carrying TR-based CYP51A variants have also developed acquired resistance to methyl benzimidazole carbamate, quinone outside inhibitor and succinate dehydrogenase (Sdh) inhibitor fungicides through target-site alterations in the corresponding fungicide target proteins; beta-tubulin (F200Y), cytochrome b (G143A), and Sdh subunit B (H270Y and H270R), respectively. Molecular typing showed that several multi-fungicide resistant strains found in agricultural soils in this study were clonal as identical isolates have been found earlier in the environment and/or in patients. Further research on the spread of different fungicide-resistant alleles from the wider environment to patients and vice versa can inform optimal practices to tackle the further spread of antifungal resistance in A. fumigatus populations and to safeguard the efficacy of azoles for future treatment of invasive aspergillosis.

scholarly journals A Rapid Method to Quantify Fungicide Sensitivity in the Brown Rot Pathogen Monilinia fructicola

Plant Disease ◽  
2009 ◽  
Vol 93 (4) ◽  
pp. 328-331 ◽  
Author(s):  
Kerik D. Cox ◽  
Kacie Quello ◽  
Ryan J. Deford ◽  
Janna L. Beckerman
Keyword(s):  
Rapid Method ◽  
Fungicide Resistance ◽  
Mycelial Growth ◽  
Brown Rot ◽  
Spore Density ◽  
Monilinia Fructicola ◽  
Chromogenic Substrate ◽  
Alamar Blue ◽  
Resistance Screening ◽  
Fungicide Sensitivity

Management of brown rot of stone fruit relies upon the application of effective fungicides that may be compromised by the development of fungicide resistance. We evaluated fungicide resistance in the brown rot pathogen, Monilinia fructicola, using Alamar blue (AB) dye, or resazurin, a chromogenic substrate that can be used as an indicator of respiration, in a 96-well microtiter format. We compared the AB method to traditional mycelial growth assays for resistance screening using 10 isolates of M. fructicola that represented a range of sensitivities to fenbuconazole. Using traditional mycelial growth assays, isolate sensitivity ranged from 17.7 to 115.3% growth on medium amended with fenbuconazole at 0.03 μg/ml relative to that on nonamended medium. Concordant results between both assays were obtained (R2 = 0.9943, P < 0.0001), but the AB method provided results within 24 h, as opposed to the 3- to 5-day period required for mycelial growth assays. We found that sensitive isolates reduced AB less than resistant isolates in the presence of fungicide. Spore density influenced the reduction of AB by M. fructicola; spectrophotometric discrimination of fungicide sensitivity was best achieved at a density of 105 spores/ml.

scholarly journals Sensitivity of Botrytis cinerea from Connecticut Greenhouses to Benzimidazole and Dicarboximide Fungicides

Plant Disease ◽  
1997 ◽  
Vol 81 (7) ◽  
pp. 729-732 ◽  
Author(s):  
J. A. LaMondia ◽  
S. M. Douglas
Keyword(s):  
Growth Rate ◽  
Botrytis Cinerea ◽  
Fungicide Resistance ◽  
Fungicide Sensitivity ◽  
Thiophanate Methyl ◽  
Dicarboximide Resistance

Botrytis cinerea was isolated from infected plants in six greenhouses in Connecticut. Forty-five isolates were evaluated in vitro to determine fungicide sensitivity to benzimidazole (benomyl and thiophanate-methyl) and dicarboximide fungicides (vinclozolin and iprodione). B. cinerea isolates with fungicide resistance were recovered from each greenhouse sampled. Benzimida-zole resistance was more common than dicarboximide resistance (74 to 76% versus 36 to 43%, respectively). Multiple fungicide resistance was common. Nineteen isolates were resistant to both a benzimidazole and a dicarboximide fungicide. The level (EC50) of resistance to dicer-boximides was low compared with resistance to benzimidazoles. Isolate growth rate was not correlated to fungicide sensitivity or EC50. Fungicide resistance was apparently unrelated to the patterns of fungicide use in greenhouses sampled.

scholarly journals Intimate genetic relationships and fungicide resistance in multiple strains of Aspergillus fumigatus isolated from a plant bulb

2021 ◽  
Vol 23 (9) ◽  
pp. 5621-5638
Author(s):  
Hiroki Takahashi ◽  
Sayoko Oiki ◽  
Yoko Kusuya ◽  
Syun‐ichi Urayama ◽  
Daisuke Hagiwara
Keyword(s):  
Aspergillus Fumigatus ◽  
Fungicide Resistance ◽  
Genetic Relationships ◽  
Multiple Strains

Fungicide resistance in Venturia effusa, cause of pecan scab: current status and practical implications

2020 ◽  
Author(s):  
Jeff Standish ◽  
Tim Brenneman ◽  
Clive Bock ◽  
Katherine Stevenson
Keyword(s):  
Fungicide Resistance ◽  
Operating Cost ◽  
Resistance Management ◽  
Research Priorities ◽  
Current Status ◽  
Future Research ◽  
Pecan Scab ◽  
Recent Developments ◽  
Benzimidazole Carbamates ◽  
Practical Implications

Pecan scab, caused by Venturia effusa, is the most economically damaging disease of pecan in the southeastern U.S. and annual epidemics are most effectively managed through multiple fungicide applications. The fungicide applications can be the single greatest operating cost for commercial growers and the return on that investment is impacted by fungicide resistance. Venturia effusa produces multiple generations of conidia per season, exhibits substantial genetic diversity, overwinters as stromata in the tree, and is under immense selection from the applied fungicides, all of which lead to a high risk for developing fungicide resistance. Since the mid-1970s, resistance or reduced sensitivity has been observed in isolates of V. effusa to the methyl benzimidazole carbamates, demethylation inhibitors, quinone outside inhibitors, organotin compounds and the guanidines. Over the last ten years, several studies have been conducted that have improved both scab management and fungicide resistance management in V. effusa. The aim of this review is to summarize recent developments in our understanding of fungicide resistance in V. effusa in the context of scab management in southeastern pecan orchards. The history, modes of action, general use of the labelled fungicides, and mechanisms and stability of fungicide resistance in V. effusa are discussed; conclusions and future research priorities are also presented.

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