"There are now plenty of drugs for infections caused by Gram-positive," he said, "and the more pressing need is for resistant Gram-negatives."

David Martin, AvidBiotics' chief executive, says the company has developed a large portfolio of proteins for Gram-negative bacteria and a smaller one for Gram-positive bacteria.

First, they discovered they could get the same cancer-suppressing effect using just vancomycin, an antibiotic that kills only “Gram-positive” bacteria.