Rapid identification of Erwinia amylovora and Pseudomonas syringae species and characterization of E. amylovora streptomycin resistance using quantitative PCR assays

Exploring Antimicrobial Peptides Efficacy against Fire Blight (Erwinia amylovora)

Antimicrobial peptides (AMPs) are a various group of molecules found in a wide range of organisms and act as a defense mechanism against different kinds of infectious pathogens (bacteria, viruses, and fungi, etc.). This study explored the antibacterial activity of nine candidates reported in the literature for their effect on human and animal bacteria, (i.e., Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa) against Erwinia amylovora (E. amylovora), the causal agent of fire blight disease on pome fruits. The antibacterial activity of these peptides against E. amylovora was evaluated in vitro using viable-quantitative PCR (v-qPCR), fluorescence microscopy (FM), optical density (OD), and transmission electron microscopy (TEM), while the in vivo control efficacy was evaluated in treating experimental fire blight on pear fruits. With a view to their safe and ecofriendly field use in the future, the study also used animal and plant eukaryotic cells to evaluate the possible toxicity of these AMPs. Results in vitro showed that KL29 was the most potent peptide in inhibiting E. amylovora cell proliferation. In addition, the results of v-qPCR, FM, and TEM showed that KL29 has a bifunctional mechanism of action (lytic and non-lytic) when used at different concentrations against E. amylovora. KL29 reduced fire blight symptoms by 85% when applied experimentally in vivo. Furthermore, it had no impact on animal or plant cells, thus demonstrating its potential for safe use as an antibacterial agent. This study sheds light on a new and potent antibacterial peptide for E. amylovora and its modes of action, which could be exploited to develop sustainable treatments for fire blight.

Identification and Characterization of Erwinia Phage IT22: A New Bacteriophage-Based Biocontrol against Erwinia amylovora

Erwinia amylovora is a quarantine phytopathogenic bacterium that is the causal agent of fire blight, a destructive disease responsible for killing millions of fruit-bearing plants worldwide, including apple, pear, quince, and raspberry. Efficient and sustainable control strategies for this serious bacterial disease are still lacking, and traditional methods are limited to the use of antibiotics and some basic agricultural practices. This study aimed to contribute to the development of a sustainable control strategy through the identification, characterization, and application of bacteriophages (phages) able to control fire blight on pears. Phages isolated from wastewater collected in the Apulia region (southern Italy) were characterized and evaluated as antibacterial agents to treat experimental fire blight caused by E. amylovora. Transmission electron microscopy (TEM) conducted on purified phages (named EP-IT22 for Erwinia phage IT22) showed particles with icosahedral heads of ca. 90 ± 5 nm in length and long contractile tails of 100 ± 10 nm, typical of the Myoviridae family. Whole genome sequencing (WGS), assembly, and analysis of the phage DNA generated a single contig of 174.346 bp representing a complete circular genome composed of 310 open reading frames (ORFs). EP-IT22 was found to be 98.48% identical to the Straboviridae Erwinia phage Cronus (EPC) (GenBank Acc. n° NC_055743) at the nucleotide level. EP-IT22 was found to be resistant to high temperatures (up to 60 °C) and pH values between 4 and 11, and was able to accomplish a complete lytic cycle within one hour. Furthermore, the viability-qPCR and turbidity assays showed that EP-IT22 (MOI = 1) lysed 94% of E. amylovora cells in 20 h. The antibacterial activity of EP-IT22 in planta was evaluated in E. amylovora-inoculated pear plants that remained asymptomatic 40 days post inoculation, similarly to those treated with streptomycin sulphate. This is the first description of the morphological, biological, and molecular features of EP-IT22, highlighting its promising potential for biocontrol of E. amylovora against fire blight disease.

Bacteriophages: Combating Antimicrobial Resistance in Food-Borne Bacteria Prevalent in Agriculture

Through recent decades, the subtherapeutic use of antibiotics within agriculture has led to the widespread development of antimicrobial resistance. This problem not only impacts the productivity and sustainability of current agriculture but also has the potential to transfer antimicrobial resistance to human pathogens via the food supply chain. An increasingly popular alternative to antibiotics is bacteriophages to control bacterial diseases. Their unique bactericidal properties make them an ideal alternative to antibiotics, as many countries begin to restrict the usage of antibiotics in agriculture. This review analyses recent evidence from within the past decade on the efficacy of phage therapy on common foodborne pathogens, namely, Escherica coli, Staphylococcus aureus, Salmonella spp., and Campylobacter jejuni. This paper highlights the benefits and challenges of phage therapy and reveals the potential for phages to control bacterial populations both in food processing and livestock and the possibility for phages to replace subtherapeutic usage of antibiotics in the agriculture sector.

Dissecting Genetic Resistance to Fire Blight in Three Pear Populations

Fire blight, caused by the bacterial pathogen Erwinia amylovora, is a persistent problem for pear (Pyrus spp.) growers in the United States. Growing resistant cultivars is one of the best options for managing fire blight. The cultivars Potomac and Old Home and the selection NJA2R59T69 display resistance to fire blight. As such, three mapping populations (El Dorado × Potomac, Old Home × Bartlett, and NJA2R59T69 × Bartlett) were developed to identify genomic regions associated with resistance to fire blight. Progeny were phenotyped during 2017 and 2018 by inoculating multiple actively growing shoots of field-grown seedling trees with E. amylovora isolate E153n via the cut-leaf method. Genotyping was conducted using the recently developed Axiom Pear 70 K Genotyping Array and chromosomal linkage groups were created for each population. An integrated two-way pseudo-testcross approach was used to map quantitative trait loci (QTLs). Resistance QTLs were identified on chromosome 2 for each population. The QTLs identified in the El Dorado × Potomac and Old Home × Bartlett populations are in the same region as QTLs that were previously identified in Harrow Sweet and Moonglow. The QTL in NJA2R59T69 mapped proximally to the previously identified QTLs and originated from an unknown Asian or occidental source. Future research will focus on further characterizing the resistance regions and developing tools for DNA-informed breeding.