Abstract
Mycoplasmal conjunctivitis was first observed in house finches (Carpodacus mexicanus) at backyard birdfeeders in the Mid-Atlantic States in 1994.3 The epidemic spread rapidly throughout the population of house finches in the Eastern U.S. and Southeastern Canada.1 The causative agent of the epidemic in songbirds, Mycoplasma gallisepticum, has long been an economically important pathogen of domestic poultry, both in the U.S. and worldwide.4 Together with other investigators, we have previously speculated that infection with M. gallisepticum may have been recently acquired by the house finch as a result of transmission from domestic poultry. Alternatively, this epidemic may have resulted from the emergence of a virulent form of a M. gallisepticum strain associated with songbirds but not previously recognized in these hosts.
To address this question we have initiated a molecular approach to determine whether the songbird strain of M. gallisepticum is a newly acquired pathogen of songbirds or whether it has a long, well-established relationship with this host. This study begins to address this question by determining the genome size of songbird isolates of M. gallisepticum and comparing this with the published genome sizes of a number of M. gallisepticum strains isolated from domestic poultry.2,5-7 Genomic DNA was purified from three M. gallisepticum isolates obtained from house finches in distinct geographic locations in 1994, 1995 and 2001, digested with the restriction enzymes, SmaI, EagI and NaeI and mobilized by pulsed field gel electrophoresis. The genome size was estimated by comparison of the DNA fragments with lambda DNA markers. All three house finch isolates produced similar banding patterns with each of the restriction enzymes tested. The estimated molecular weight of 975 kilobases is smaller than the 1030–1070 kilobase genomes previously reported for M. gallisepticum isolates from poultry.
Literature Cited
1. Dhondt AA, DL Tessaglia, RL Slothower. 1998. Epidemic mycoplasmal conjunctivitis in house finches from eastern North America. J. Wildl. Dis. 34: 265–80.
2. Gorton TS, MS Goh, SJ Geary. 1995. Physical mapping of the Mycoplasma gallisepticum S6 genome with localization of selected genes. J. Bacteriol. 177: 259–63.
3. Ley DH, JE Berkhoff, JM McLaren. 1997. Mycoplasma gallisepticum isolated from house finches (Carpodacus mexicanus) with conjunctivitis. Avian Dis. 40: 480–3.
4. Ley DH, HW Yoder. 1997. Mycoplasma gallisepticum infection. In: BW Calnek, HJ Barnes, CW Beard, LR McDougald, YM Saif, eds. Diseases of Poultry. 9th ed. Iowa State University Press, Ames, IA. pp. 194–207.
5. Neimark HC, CS Lange. 1990. Pulse-field electrophoresis indicates full-length Mycoplasma chromosomes range widely in size. Nucleic Acids Res. 18: 5443–8.
6. Pyle LE, LN Corcoran, BG Cocks, AD Bergemann, JC Whitley, LR Finch. 1988. Pulsed-field electrophoresis indicates larger-than-expected sizes for Mycoplasma genomes. Nucleic Acids Res. 16: 6015–25.
7. Tigges E, FC Minion. 1994. Physical map of Mycoplasma gallisepticum. J. Bacteriol. 176: 4157–9.