Does Borrelia burgdorferi produce a neurotoxin ?

Bacteria produce only two types of toxins: endotoxins, which are non-secreted lipopolysaccharides (LPSs) that make up a large part of the cell wall of gram-negative bacteria; and, exotoxins that are secreted by some gram-positive bacteria and a few strains of gram-negative bacteria.

At one time, Borrelia burgdorferi, was thought to possess an endotoxin since a product isolated from B. burgdorferi was reported to be pyrogenic for rabbits, mitogenic for human mononuclear cells and mouse spleen cells, capable of clotting limulus lysate (a diagnostic test for LPS), and cytotoxic for mouse macrophages; these are properties generally ascribed to bacterial LPS (1). However, subsequent studies revealed the absence of lipid A and other chemical structures characteristic of classic gram-negative endotoxins (2). Although B. burgdorferi does not produce an endotoxin, it does possess lipoproteins that interact with Toll-like receptors (TLRs) on the surface of mammalian cells that comprise the innate immune system, to cause them to release inflammatory products that result in tissue damage and some of the clinical manifestations of Lyme disease (3-9).

There is abundant evidence to show that treatment with a short course of oral antibiotics is likely to cure active infection by B. burgdorferi (10); however, it is possible that some biologically active lipoproteins from dead bacterial cells persist in host tissues for periods of time after the initial infection has been cured.

Although some claim that B. burgdorferi produces a potent neurotoxin, there is no published, peer-reviewed evidence indicating that B. burgdorferi is an exotoxin-producing bacterium. In fact, the genomic sequence data do not reveal the presence of genes that encode for either key structural elements of any known bacterial exotoxin, or components of a secretory apparatus required for the export and delivery of an exotoxin (11).

In view of these considerations, treatment regimens for Lyme disease based on the neutralization — or removal by chelation– of a yet-to-be-identified neurotoxin should be viewed with much skepticism; such quackery is not only likely to be a waste of time and money, but also has the potential to cause great harm. There is no clinical evidence to indicate that such treatments are safe or effective.

References

1. Beck, G., G.S. Habicht, J.L. Benach, and J.L. Coleman. 1985. Chemical and biological characterization of a lipopolysaccharide extracted from the Lyme disease spirochete, (Borrelia burgdorferi). J. Infect. Dis. 152: 108-117.

2. Takayama, K., R.J. Rothenberg, and A.G. Barbour. 1987. Absence of lipopolysaccharide in the Lyme disease spirochete, Borrelia burgdorferi. Infect. Immun. 55: 2311-2313.

3.Wooten, R.M. and J.J. Weis. 2001. Host-pathogen interactions promoting inflammatory Lyme arthritis: use of mouse models for dissection of disease processes. Current Opinion in Microbiol. 4: 274-279.

4. Aliprantis, A.O., R.B. Yang, M.R. Mark, et al. 1999. Cell activation and apoptosis by bacterial lipoproteins through Toll- like receptor-2. Science 285: 736-739.

5. Brightbill, H.D., D.H. Libraty. S.R. Krutzik, et al. Host defense mechanisms triggered by microbial lipoproteins through Toll-like receptors. Science 285: 732-736.

6. Hirschfield, M., C.J. Kirschning, R. Schwandner. et al., 1999. Inflammatory signaling by Borrelia burgdorferi lipoproteins is mediated by Toll-like receptor-2. J. Immunol. 163: 2382-2386.

7. Lien, E., T.J. Sellati, A. Yoshimura, et al. 1999. Toll-like receptor- 2 functions as a pattern recognition receptor for diverse bacterial products. Chemistry 274: 33419-33425.

8. Ozinsky, A., D.M. Underhill, J.D. Fontenot, et al. 2000. The repertoire for pattern recognition of pathogens by the innate immune system is defined by cooperation between Toll-like receptors. Proc. Nat. Acad. Sci. 97: 13766-13771.

9. Alexopoulou, L., V. Thomas, M. Schnare, et al. Hyporesponsiveness to vaccination with Borrelia burgdorferi Osp A in humans and in TLR-1 and TLR-2 deficient mice. Nature Medicine 8: 878-884.

10. Wormser, G.P., R.J. Dattwyler, E.D. Shapiro, et al. 2006. The clinical assessment, treatment, and prevention of Lyme disease, human granulocytic anaplasmosis, and babesiosis: clinical practice guidelines by the Infectious Disease Society of America. Clin. Infect. Dis. 43: 1089-1134.

11. Fraser, C., S. Casjens, W.M. Huang, et al. (1997). Genomic sequence of a Lyme disease spirochete, Borrelia burgdorferi. Nature 390: 580-586.

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