Washington: Until now, scientists thought that disease-causing bacteria left on the toy by a strep- infected child was responsible for transferring the disease from the first child to the second.

However, a new research at Rockfeller University has found that the culprit sometimes might not be the bacteria, but a virus that infects and destroys the bacteria. Called a bacteriophage, this "bacteria- eating" virus causes disease by transferring toxins and other disease-causing genes between bacteria.

The findings, reported in the latest issue of 'Infection and Immunity', show for the first time that bacteriophage, or phage – previously thought not to be infectious to humans – may be a new target for fighting certain bacteria that produce toxins.

"Controlling the phage may be as important as controlling the bacteria. It's possible that phage present in the saliva of a child or another individual can cause the conversion of an existing non-toxigenic organism to a toxigenic one. We always believed that phage were not infectious to humans, but in a sense, they are," said senior author Vincent A Fischetti, from the Rockefeller University.

Scientists classify certain bacteria such as those causing scarlet fever, diphtheria and E coli O157, a source of food poisoning in contaminated meats, as toxigenic, meaning that these microbes produce toxins – transported by phage – that cause disease.

People can carry colonies of bacteria, such as strep, without being sick if the microbe doesn't carry a toxin-encoded phage. But when a toxin-producing phage moves to a non-virulent bacterium, it carries with it a toxin gene that is part of the phage genome, and transfers that gene to the new organism. This process, called lysogenic conversion, transforms the harmless microbe into a virulent bug.

The bacterium picks up the phage from a factor in human saliva that is secreted from cells in the pharynx – the part of the alimentary canal between the cavity of the mouth and the esophagus – and causes the phage to become active and burst out of the bacterium.

ANI