Oxytetracycline and Streptomycin Resistance Genes in Xanthomonas arboricola pv. pruni, the Causal Agent of Bacterial Spot in Peach

Abstract

Xanthomonas arboricola pv. pruni (Xap) causes bacterial spot, a major worldwide disease of Prunus species. Very few chemical management options are available for this disease and frequent applications of oxytetracycline (OTC) in the United States peach orchards have raised concerns about resistance development. During 2017–2020, 430 Xap strains were collected from ten peach orchards in South Carolina. Seven OTC-resistant (OTCR) Xap strains were found in 2017 and 2020 from four orchards about 20–270 km apart. Interestingly, the seven strains were also resistant to streptomycin (STR). Six strains grew on media amended with ≤100 μg/mL OTC, while one strain, R1, grew on ≤250 μg/mL OTC. Genome sequence analysis of four representative OTCR strains revealed a 14–20 kb plasmid carrying tetC, tetR, and strAB in each strain. These three genes were transferable to Xanthomonas perforans via conjugation, and they were PCR confirmed in all seven OTCR Xap strains. When tetC and tetR were cloned and expressed together in a sensitive strain, the transconjugants showed resistance to ≤100 μg/mL OTC. When tetC was cloned and expressed alone in a sensitive strain, the transconjugants showed resistance to ≤250 μg/mL OTC. TetC and tetR expression was inducible by OTC in all six wild-type strains resistant to ≤100 μg/mL OTC. However, in the R1 strain resistant to ≤250 μg/mL OTC, tetR was not expressed, possibly due to the presence of Tn3 in the tetR gene, and in this case tetC was constitutively expressed. These data suggest that tetC confers OTC resistance in Xap strains, and tetR regulates the level of OTC resistance conferred by tetC. To our knowledge, this is the first report of OTC resistance in plant pathogenic xanthomonads.

Identification and comparison of somatic antigen composition for bacteria from Providencia genus

“…TetA is responsible for the synthesis of the tetracycline efflux MFS transporter [34]. The tetC and tetR genes are required for the tetracycline resistance-associated transcriptional repressor TetC and tetracycline resistance transcriptional repressor TetR production [35, 36]. The insertion of transposon led to breakdown of the gene encoding the flippase synthesis.…”

Targeted delivery of oxytetracycline to the epidermal cell junction and stomata for crop protection

“…aS: sensitive; R: resistant.bThe OTC resistance-threshold was determined on NA amended with different concentrations of OTC. 15 …”

“…12,16 Twig infection from Xap leads to twig cankers, often observed in spring, and is considered a major inoculum source for leaf and fruit infection. 14,15,17 Bacterial spot of peach results in reduced orchard productivity, reduced quality and marketability of the fruit, and increased nursery cost. 12…”

“…Early defoliation from bacterial spot infection causes weakened trees and impacts winter hardiness. 15 Normally, infected fruit is unmarketable due to necrotic spotted lesions. It has been reported that under optimal environmental conditions the disease can affect 100% of the fruit.…”

Uptake of the Plant Agriculture-Used Antibiotics Oxytetracycline and Streptomycin by Cherry Radish─Effect on Plant Microbiome and the Potential Health Risk

“…The astounding ability of antibiotics to cure deadly diseases makes plant pathologists quickly recognize the potential of antibiotics for treating plant bacterial diseases . Since the 1950s, antibiotics have been successfully used to treat fire blight of apples and pears, leaf spot disease of peach and nectarine, “Huanglongbing” of citrus tree, and lethal yellowing disease in elm and coconut palm trees, and so on. − However, along with the introduction of antibiotics into plant agriculture, concerns have been raised regarding the uptake and translocation of applied antibiotics to the receiving plants and associated health risks to humans and plants. − Today, the most commonly used antibiotics in plant agriculture are oxytetracycline and streptomycin, , both of which have broad-spectrum antibacterial activity by the mechanism of binding to the 30S ribosomal subunit to prevent protein synthesis. A recent study estimated that annually 63 tonnes of streptomycin and 7 tonnes of tetracycline were sprayed on the rice crop in South East Asia alone .…”