Erwinia amylovora populations resistant to oxolinic acid in Israel: prevalence, persistence and fitness

Abstract

Oxolinic acid (OA) has been the only bactericide used against fire blight in pear and quince orchards in Israel since 1998. OA-resistant Erwinia amylovora strains ( Ea-OA R ) were detected in several orchards in two restricted areas in the northern Galilee region during 1999-2001. In the following years, resistant strains could not be detected in some of these locations. Documenting the fate of Ea-OA R strains in commercial orchards at eight sites in northern Israel during 2000/03 revealed that the resistant population appeared irrespective of the number of sprays applied and the severity of the disease. The persistence of the Ea-OA R populations varied from site to site, ranging from 4 to 20 months; these differences could be attributed to the fire blight management activities of growers. Comparative studies on the fitness of Ea-OA R and E. amylovora strains sensitive to OA ( Ea-OA S ) were conducted in vitro and in planta using two strains of each group. In four of the six comparisons, disease incidence on detached blossoms inoculated with Ea-OA S was significantly higher than that on blossoms inoculated with Ea-OA R . In two experiments conducted on 8-year-old pear trees grown under netting, the colonization of Ea-OA S in blossoms, annual shoots and perennial spurs was significantly higher than that of the Ea-OA R . In two experiments conducted on 2-year-old trees grown under netting in an experimental station, the incidence of shoots exhibiting fire blight symptoms and the rate of symptom progress within the branches were significantly higher in trees inoculated with Ea-OA S than in those inoculated with Ea-OA R . The results of this study suggest that OA-resistant E. amylovora strains have lower fitness than wild-type strains. These findings may have implications for fire blight management.

Use of antibiotics in plant agriculture

“…Some of the oxolinic acid-resistant isolates of B. glumae also exhibited crossresistance to other quinolones, including ciprofloxacin, a fluoroquinolone important in clinical medicine (18). Just two years after oxolinic acid was introduced for control of fire blight in Israel, oxolinic acid-resistant isolates of E. amylovora were detected in several orchards (21). The rapid emergence of resistance to oxolinic acid diminished interest in the use of this antibiotic for sustainable disease control on plants in other countries.…”

Amino Acid Substitutions in GyrA ofBurkholderia glumaeAre Implicated in Not Only Oxolinic Acid Resistance but Also Fitness on Rice Plants

“…Kleitman et al (19) reported that OA-resistant E. amylovora strains have lower fitness than wild-type strains under no OA treatment. Here, analysis of bacterial populations in rice spikelets showed that the Ser83Arg recombinants grew less than Pg-10, while the growth abilities of the other OA-resistant recombinants were significantly reduced.…”

“…Furthermore, OA-resistant E. amylovora strains reportedly have lower fitness than wildtype strains (19). However, the implications of OA resistance in the fitness of the bacteria on their host plants remain unclear.…”

Antimicrobial Resistance with Special Emphasis on Pathogens in Agriculture

“…However, populations of OA-resistant E. amylovora fluctuated, with OA-resistant strains becoming undetectable in orchards where they previously occurred. Laboratory analyses of OA-resistant strains suggested that these strains were reduced in fitness compared to OA-sensitive strains [39]. Analysis of OA-resistant strains of Burkholderia glumae also showed that the strains were reduced in fitness, as these strains could not survive in rice paddy fields [40].…”