Mycoplasmal mastitis in dairy herds

Mycoplasmas are the smallest self-replicating organisms known. They have a worldwide distribution as free-living saprophytes or as parasites of humans, mammals, reptiles, fish, arthropods, and plants [1]. Mycoplasmas lack cell walls, have simple-surface exposed plasma membranes, possess minute genomes, and have limited metabolic capabilities compared with other bacterial groups [2]. The absence of cell walls and cell wall associated proteins renders mycoplasmas resistant to the action of antibiotics that interact with these proteins [3]. Because of their limited genetic potential, mycoplasmas usually require intimate association with mammalian cell surfaces and an enriched medium containing a peptone, yeast extract, and animal serum for in vitro growth [3]. Despite their genetic simplicity and an image as impotent microorganisms [4], mycoplasmas are considered major animal pathogens in animal production units worldwide [5]. The introduction of molecular techniques to taxonomy, including the comparison of 16S rRNA and other conserved gene sequences, as well as genomic restriction patterns have been effectively used in species and strain identification [2,6]. Mycoplasmal infections follow a chronic course because the organisms usually live in harmony with their host. Mycoplasmas exhibit a rather strict host, tissue, and organ specificity, probably reflecting their nutritionally precise nature and obligate parasitic mode of life [2]. They have been found, however, in hosts and tissues different from their normal habitats [1]. Several species of Mycoplasma have been found as the cofactors or actual cause of diseases of the respiratory and urogenital tracts, joints, and mammary gland of the bovine [7,8].