Genetic variation among Mycoplasma agalactiae isolates detected by the variant surface lipoprotein gene (vspA) of Mycoplasma bovis

Multiple restriction fragments, homologous to the previously described Mycoplasma bovis vspA gene, were identified in the chromosome of Mycoplasma agalactiae. The vspA, a representative variable surface lipoprotein gene of the vsp gene family, and four synthetic oligonucleotides, representing sequences complementary to selected regions of the vsp genes, were used as probes against digested chromosomal DNAs of several M. agalactiae clinical isolates. The resulting Southern blot analysis demonstrated a marked DNA polymorphism of multiple vspA-related fragments among the isolates. An oligonucleotide representing a conserved 5′-region common to all known vsp genes, was found to hybridize to multiple M. agalactiae genomic fragments while the other three oligonucleotides, representing distinct repetitive structures within the coding region of three known vsp genes (vspA, vspE, and vspF), failed to react. These results argue for the possible existence of a gene family in M. agalactiae analogous to the vsp system of M. bovis but comprised of diverse genes.