Cloning of Mycoplasma synoviae genes encoding specific antigens and their use as species-specific DNA probes.

A genomic library of Mycoplasma synoviae (MS) was generated by using bacteriophage lambda gt11 as a cloning and expression vector. Identification of recombinant clones highly specific to MS was achieved by screening the library for expression of MS proteins with polyclonal antiserum that had been preadsorbed with 6 heterologous avian mycoplasma species antigens. Expression of the recombinant clones in Escherichia coli followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the total cell lysates and immunoblot yielded a predominant reactive fusion protein of 165 kD. Two clones (MS2/28 and MS2/12) that yielded inserts of different size were selected. The 2 MS DNA inserts were subcloned in a plasmid vector, labeled with digoxigenin, and used as probes for the specific recognition of several MS strains. A high degree of conservation was demonstrated for the MS2/12 and MS2/28 genes in tested MS strains. In addition, neither DNA fragment recognized any other avian mycoplasma species (M. gallisepticum, M. meleagridis, M. gallinarum, M. iners, M. anatis, and M. iowae), thus indicating their high specificity to MS. The sensitivity of the slot blot hybridization method using digoxigenin-labeled MS2/12 and MS2/28 probes for direct detection of MS from broth cultures of field isolates was 10(5) colony-forming units/ml. These results demonstrate the effectiveness of adsorbed antisera for the isolation of species-specific mycoplasma DNA and the potential for its use as probes for the specific and direct detection of MS from broth cultures of field isolates.