SAN FRANCISCO -- After being shelved for more than 50 years, an antibiotic candidate, which was once regarded as less promising in killing bacteria, has caught the attention of researchers for its special ability to cure a popular disease, according to a new study.

The drug, called pentyl pantothenamide, was found to be able to stop the growth of E. coli, a large group of bacteria that can cause diarrhea, urinary tract infections, respiratory illness, pneumonia and other illnesses, though it may not kill the bacteria completely.

Among a wider class of pantothenamides that have broad spectrum activity against many bacteria, only one particular molecule is much more effective against E. coli, the study found.

The key answer to the mystery is Vitamin B5, which is used to metabolise energy that humans find in their diet, while bacteria have to create it via a media called PanDZ complex.

Lab experiment results showed that pentyl pantothenamide targets the PanDZ complex, preventing E. coli from making Vitamin B5 and depriving it of energy needed for its further growth.

With the help of X-ray technology, the researchers mapped the structure of the complex and discovered that the antibiotic binds to the bacteria only in the presence of a particular compound created by the bacteria using three different enzymes.

The study was conducted by an international team led by senior researcher Michael Webb of the British University of Leeds, which was published in a recent edition of the journal Biochemistry.

The researchers are trying to find a molecule capable of mimicking the final compound which boosts the action of the antibiotic in killing bacteria like E. coli, in a hope for designing new drugs for attacking E. coli in a more effective way.