Abstract

Mycoplasma gallisepticum (MG) conjunctivitis emerged in 1994 as a disease of free-ranging house finches (Carpodacus mexicanus) in the eastern United States and has since spread to house finches throughout their entire eastern range. The resulting epidemic of MG conjunctivitis produced an unprecedented decline of eastern house finch populations, and the endemic disease remains associated with repeating seasonal peaks of disease and limitation of host populations. Random amplification of polymorphic DNA (RAPD) had indicated a single RAPD profile among house finch isolates, suggesting a single point source of origin and one ‘strain’ common to this outbreak. However, genomic variability of MG house finch isolates has recently been identified by PCR-RFLP and nucleotide sequencing of the pvpA gene. These findings suggested that house finch MG isolates may be more polymorphic than previously recognized and/or evidence of molecular evolution.

We have seen some evidence of genomic variability among MG isolates by RAPD fingerprinting. However, RAPD ‘fingerprints’ are prone to variability, and may be difficult to reproduce and standardize, making interpretation challenging and somewhat subjective. To explore the possibility of genomic variability among house finch isolates of M. gallisepticum, we selected samples from our archive of isolates to analyze by RAPD and amplified-fragment length polymorphism. Amplified-fragment length polymorphism (AFLP) analysis is a selective restriction fragment amplification technique based on the ligation of adapters (linkers and indexers) to genomic restriction fragments followed by a PCR-based amplification with adapter-specific primers. This analysis may approach the ideal genotyping method, which produces results that are consistent from laboratory to laboratory and allows unambiguous comparative analyses and the establishment of reliable databases. The AFLP technique has been successfully used to explore the genomic variability of several Mycoplasma spp. Analyses of MG house finch isolates by RAPD and AFLP allows us to more definitively explore the potential genomic variability of these isolates and their molecular epidemiology especially with respect to temporal and geographic relationships. These analyses also generate comparative data between RAPD and AFLP methodologies, providing an opportunity to evaluate the utility of AFPL for MG typing.