Colorful bacteria more dangerous

A new study in the July 18 issue of The Journal of Experimental Medicine shows that gold-colored bacteria are more harmful than their unpigmented relatives. A group of scientists led by Victor Nizet (UCSD, San Diego, CA) have discovered that the molecules that give certain bugs their color also help them resist attack by immune cells called neutrophils.

Scientists and clinicians have known for many years that gold-colored strains of a bacterium called Staphylococcus aureus tend to be cause more disease than colorless strains. The color of these bugs comes from anti-oxidant molecules called carotenoids. Similar molecules also give carrots their color and are often touted for their ability to boost the immune system.

Nizet and colleagues now show that these pigmented molecules help S. aureus defuse damaging molecules that are produced by neutrophils in order to kill the bacteria. When the researchers removed the carotenoids from the bacteria, they became more vulnerable to immune attack. Nizet suggests that drugs that inhibit carotenoid synthesis might be useful for treating S. aureus infections, which can quickly develop resistance to traditional antibiotics.

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