Antibiotic selective markers and spirochete genetics.

Until very recently, the pathogenic spirochetes have been refractory to genetic manipulation. This has been due, in part, to difficulties with in vitro growth and the genetic distance that spirochetes are from typical Gram-negative and Gram-positive organisms. Insertional mutagenesis and other genetic techniques are now possible in some of the pathogenic spirochetes such as Borrelia burgdorferi, Brachyspira (Serpulina) hyodysenteriae, Leptospira sp., and Treponema denticola. However, organisms such as Treponema pallidum, which cannot be grown in vitro, are still not amenable to genetic manipulation. These recent advances have paved the way for more detailed genetic studies of transcriptional regulation, protein function, protein localization, metabolic capabilities, motility, and pathogenic nature of this group of spirochetes. This review article will discuss the current repertoire of antibiotic markers that are useful for spirochetal genetic manipulation. Further advances in selectable markers and shuttle vectors will allow researchers to complete Koch's molecular hypothesis for various virulence genes of the pathogenic spirochetes and increase the overall understanding of these challenging bacteria.