A chance discovery could lead to a much-needed new class of antibiotics, according to a new study.
The possible breakthrough is one of the most exciting events in Professor Jeremy Lakey's 30 years researching antibacterials.
And when the British researcher who made the chance discovery saw what happened, he repeated the experiment several times because he did not believe it.
In a paper published in the journal Molecular Microbiology, a team from Newcastle University described studying a protein derived from E.coli bacteria, called Colicin N, which kills competing bacteria in a very efficient way. Just one molecule of this protein can kill a whole cell.
They divided the protein into three parts: a receptor, which helps the protein lock-on to the bacteria; a toxic part that punches holes in the membrane of the bacteria to kill it; and a 'tail-like' part.
The 'tail' was thought to help the protein sneak into the cell but assumed to be harmless to the bacteria itself.
They wanted to see what effect each part of the protein would have on E.coli bacteria and were amazed to see when they introduced the translocation 'tail' into the environment of the bacteria, it killed them.
The discovery, that such a simple part of a protein can kill a bacteria, could mean that new antibiotics derived from this part could be developed.
There are increasing concerns that overuse of antibiotics will lead to bacteria developing immunity to the drugs. By targeting only E.coli-like bacteria, the new molecule shows promise in combating an increasingly important class of antibiotic resistant infections.
Dr Chris Johnson, the researcher who made the key discovery, said: "When I saw what had happened I didn't believe it.
"So we repeated it several times and the same thing happened, the bacteria died.
"This was certainly a result that we weren't expecting. We don't really know how this is all working so we will be looking at this in much more detail but it looks promising."
Currently, one stumbling block to the development of new protein based antibiotics is their complicated structure.
Prof Lakey, who leads the team that made the breakthrough, said: "The beauty of this is that the 'tail' of the protein is very simple and it will be relatively easy to make new antibiotics out of it.
"Using the whole protein would just be too complicated."
The research is still at an early stage, the professor of structural biochemistry at Newcastle University's Centre for Bacterial Cell Biology said.
"It kills bacteria by a new and as yet unknown mechanism, so we need to do a lot more work to discover exactly what is happening here and whether it could be used for new drugs.
"But it is unlike anything I have seen before and one of the most exciting things I have seen in 30 years research on antibacterials."