Enzyme Helps Flesh-Eating Bacteria to Survive

Flesh-eating bacteria escape
immune defence;
© NCI Visuals Online

The research, carried out at the University of California, San Diego School of Medicine, focuses on the major human pathogen group A Streptococcus. “These findings suggest a novel approach to treating serious Strep infections, such as flesh-eating disease, by assisting our body’s own defence system,” said Victor Nizet, M.D., associate professor at Children’s Hospital, San Diego.

The investigators examined the interaction of Strep bacteria with neutrophils, specialized white blood cells that play a front line role in human’s immune defence against pathogenic microbes. Recent research by European investigators had shown that neutrophils are particularly effective defenders because they release “nets” composed of DNA and toxic compounds to entrap and kill invading bacteria.

In the current study, the scientists proved that disease-causing Strep release an enzyme that degrades these DNA nets, thereby allowing the organism to escape the neutrophil net and spread in body tissues.

The team used a molecular genetic approach for their studies, knocking out the gene encoding the DNA-degrading enzyme from a pathogenic Strep strain. “Deprived of this single enzyme, the mutant Strep strain was easily killed by human neutrophils”, said lead author John Buchanan, Ph.D., research scientist in the UCSD department of paediatrics. “In addition, the mutant Strep bacteria no longer produced a spreading infection when injected into the skin of experimental mice.”

The researchers also examined whether the DNA-degrading enzyme could represent a target for therapy. Mice experimentally infected with Strep were treated by injecting a chemical inhibitor of the DNA-degrading enzyme at the site of infection. A dramatic reduction in bacterial counts and tissue injury was observed following the inhibitor treatment.

MEDICA.de; Source: University of California, San Diego