NYU scientists discover dangerous new method for bacterial toxi...(wn to afflict dairy cows sheep and goats...)

In treating mastitis, veterinarians have tried to get around the vexing issue of antibiotic resistance with a new strategy that uses bacteriophages to attack the infection-causing microbes. When they modeled that phage therapy in the lab, however, the NYU researchers observed a phage-mediated transfer of pathogenic S. aureus genes to L. monocytogenes in raw milk. The unwitting selection of a phage with similar properties for mastitis therapy could abet the transfer of new toxin genes, Dr. Novick warns. Given that possibility, he suggests that all phages being considered for mastitis treatments should be tested beforehand to ensure they couldn't be used as bacterial DNA conduits.

Most bacteriophages have a very narrow host range and are often limited to different strains, or variants, of the same bacterial species. "Phages normally have a pretty specific cell receptor that they must find to infect the cell," Dr. Novick explains. The ability of several Staphylococcus-specific phages to infect Listeria with high efficiency, he says, suggests that the two unrelated bacterial species share a similar receptor, possibly a protein protruding from the cell where the phage can dock.

Bacteriophages also generally kill their infected hosts by bursting open the cells, a process that forms obvious plaques, or clear circles, on a lawn of bacteria in a Petri dish. If a phage does not form plaques on a specific bacterial strain, researchers usually conclude that the strain is not susceptible to phage infection. Surprisingly, the genetic transfer observed by Drs. Chen and Novick occurred even though the phages did not form telltale plaques on the L. monocytogenes cell cultures. "The transfer is happening by stealth, silently, without anyone noticing," Dr. Novick says. '/>"/>