APPLICATION OF FATTY ACID CLASS ANALYSES FOR THE DETECTION AND IDENTIFICATION OF ERWINIA AMYLOVORA

A fatty acid profile library for Erwinia amylovora has been established based on 143 strains of the bacterium. The library is made up of seven fatty acid classes: unsaturated acids (43%), saturated straight chains (41%), hydroxy substituted acids (7%), cyclic acids (3%), saturated branched chains (1%), saturated straight chains (1%) and unsaturated branched chains (4%). When three strains of E. amylovora were grown for 1, 3, or 6 days on four culture media (GYCA, KB, NA and TSA) at 27C, growth was most consistent for 3 days on TSA. Percentages of fatty acid classes were similar between original location (country) of isolate and host plant, except for the Rubus isolates, which showed a slight increase in the cyclic acids. In the "amylovora" group, five species of Erwinia can be differentiated through a species identification key.

When nine streptomycin-resistant (SR) and nine strep-susceptible (SS) strains of E. amylovora were grown on TSA for 3 days, the percentage of cyclic acids were consistently lower for the SR strains (3.1% of total fatty acids) than for the SS strains (7.1%). However, the reverse was observed for unsaturated acids (SR strains 37.5% and SS strains 32.9% of total). These differences were reflected in the saturated to unsaturated acid ratios (SR strains 1.2 and SS strains 1.5). Thus strep-resistance may be predicted by determining such ratios using gas liquid chromatography.

Recently, fatty acid class analysis was successfully used for the definite identification of E. amylovora isolates from Egypt (1985), Bulgaria (1987) and Yugoslavia (1989).

The use of the E. amylovora fatty acid library was also used as a detection tool for the identification of Erwinia-like organisms from plant tissues. A total of 37 bacterial isolates, recovered from calyx tissues of several apple varieties and resembling the blight pathogen, were proven not to be E. amylovora.