MĪ-kro-sins n. One strain of bacteria, called Escherichia coli Nissle 1917, has tiny proteins called microcins that may help E. coli’s host fight pathogens that cause gut inflammation, researchers at the University of California, Irvine report online October 31 in Nature. E. coli Nissle’s microcins killed diarrhea-inducing bacteria called Salmonella enterica in the guts of infected mice.