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Metastatic talents of toxic shock germ.

The highly invasive bacterium Staphylococcus aureus, responsible for such diverse maladies as pimples, food poisoning, blood poisoning, cystitis, endocarditis, pneumonia, severe infections and toxic shock syndrome, may spread through the body in the same way that metastasizing cancer cells do. S. aureus's capacity to bind to a molecule found in the matrix between cells may allow the bacterium to move in and out of the bloodstream by slipping through vascular walls and into tissues, report J.D. Lopes of the Ludwig Institute for Cancer Research in Sao Paulo, Brazil, and colleagues in the July 19 SCIENCE.

The molecule, laminin, is a protein that helps make up the basal laminae -- ultra thin membranes that separate the body's epithelial, or lining, cells from connective tissue. In order for cells to metastasize, they must be able to stick to the surface over which they are to migrate. S. aureus has surface receptors for laminin, which seem to allow the bacteria to stick, or bind, to the basal laminae.

S. aureus's ability to cross vascular basal laminae, and so invade the bloodstream, is "critical for the organism's pathogenicity," says Lopes. And therefore, the scientists suggest, the bacterium's laminin receptors may be responsible for S. aureus's virulence. To support this argument, the researchers also showed that Staphylococcus epidermis, a non-invasive, non-pathogenic cousin germ, has no receptors for laminin; implying that S. epidermis' lack of virulence is due to a lack of laminin receptors.

In addition, the researchers demonstrated that, like S. aureus, certain mouse cancer cells have laminin receptors, which suggests a common mechanism for invasion by two very different pathogens. Laminin receptors have been correlated with invasiveness in tumor cells.

The new findings are important because they shed light on the biochemistry of viulence, says Bruce Hannah, director of clinical microbiology at Bellevue Hospital at New York University Medical Center, in New York City. Hannah says S. aureus is a "sophisticated" organism, "replete with pathogenic potential." If the virulence of S. aureus really depends on its laminin receptors, he says, then agents that block those receptors or a vaccine that prevents adherence could be developed as alternatives to antibiotics. (Antibiotics are becoming less reliable, as pathogens develop resistance to them.)

However, Hannah cautions that Lopes and colleagues have yet to demonstrate that laminin receptors are "the true virulence mechanism." And, he adds, "very rarely does pathogenicity rest on a single trait."
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Author:Dusheck, Jennie
Publication:Science News
Date:Jul 20, 1985
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