Phage Cocktail in Combination with Kasugamycin as a Potential Treatment for Fire Blight Caused by Erwinia amylovora

Abstract

Recently, there has been an increasing number of blight disease reports associated with Erwinia amylovora and Erwinia pyrifoliae in South Korea. Current management protocols that have been conducted with antibiotics have faced resistance problems and the outbreak has not decreased. Because of this concern, the present study aimed to provide an alternative method to control the invasive fire blight outbreak in the nation using bacteriophages (phages) in combination with an antibiotic agent (kasugamycin). Among 54 phage isolates, we selected five phages, pEa_SNUABM_27, 31, 32, 47, and 48, based on their bacteriolytic efficacy. Although only phage pEa_SNUABM_27 showed host specificity for E. amylovora, all five phages presented complementary lytic potential that improved the host infectivity coverage of each phage All the phages in the cocktail solution could lyse phage-resistant strains. These strains had a decreased tolerance to the antibiotic kasugamycin, and a synergistic effect of phages and antibiotics was demonstrated both in vitro and on immature wound-infected apples. It is noteworthy that the antibacterial effect of the phage cocktail or phage cocktail-sub-minimal inhibitory concentration (MIC) of kasugamycin was significantly higher than the kasugamycin at the MIC. The selected phages were experimentally stable under environmental factors such as thermal or pH stress. Genomic analysis revealed these are novel Erwinia-infecting phages, and did not encode antibiotic-, virulence-, or lysogenic phage-related genes. In conclusion, we suggest the potential of the phage cocktail and kasugamycin combination as an effective strategy that would minimize the use of antibiotics, which are being excessively used in order to control fire blight pathogens.

Optimizing the formulation of Erwinia bacteriophages for improved UV stability and adsorption on apple leaves

“…Myovirus morphology phages having rigid contractile tail fiber are the majority, while phages having podovirus and siphovirus morphology have been rarely reported [ [51] , [52] , [53] ]. The present study used previously isolated phages as representatives of myophages, Lossenervirus for pEa_SNUABM_27 [ 30 ], and Fifi451 [ 54 ]; Eneladusvirus for pEa_SNUABM_47 [ 23 ]; unknown for Fifi318. Phages are reportedly susceptible to UV radiation [ 34 , 55 ].…”

“…Most solar UV radiation reaching the Earth's surface comprises longer-wavelength UV-A and UV-B rays, which have minimal effects on DNA damage [ 59 ]. Likewise, the previous study that employed UV-C for the UV protection assay, the protection efficacy of the auxiliary agents could not be appropriately appreciated [ 30 ]. To simulate the actual damage phages might receive from sunlight, we employed a solar simulator capable of emitting light in the 270–400 nm range, encompassing all wavelengths from UV-A, UV-B, and UV-C [ 60 ].…”

“…The sole reference strain allowed for research in South Korea, Erwinia amylovora TS3128 was used in the study. Previously reported phages, pEa_SNUABM_27 and pEa_SNUABM_47, were isolated from the river near diseased orchard and used in further assays [ 23 , 30 ]. Phage Fifi318 and Fifi451 were kindly provided by Dr. Eunjung Roh from the Rural Development Administration of Korea.…”

“…Phages can be isolated in nature, are highly specific, and only kill their target bacterial pathogens, unlike antibiotics that cause dysbiosis in the rhizosphere and phyllosphere [ [27] , [28] , [29] ]. Furthermore, the combined use of phages and antibiotics has been suggested to reduce the use of antibiotics while optimizing the antimicrobial effect [ 30 , 31 ].…”

The Biotechnological Application of Bacteriophages: What to Do and Where to Go in the Middle of the Post-Antibiotic Era

“…Several strategies involve the integration of antibiotics with phage cocktails to optimize the biocontrol potential of phages [ 80 , 81 , 82 ]. Kim et al investigated the synergistic efficacy of a phage cocktail combined with kasugamycin, an aminoglycoside-class antibiotic used in agriculture for fire blight control [ 83 ]. Notably, the individual phages within the cocktail led to a reduction in E. amylovora cell count, ranging from 1.2 to 3.5 log CFU/mL, and a remarkable synergy among the phage cocktail was observed, resulting in a reduction of −3.7 log CFU/mL in vitro.…”