LONDON, Feb 1 (Reuters) - Motif Bio, which is working on a range of antibiotics, is planning to raise at least 4 million pounds ($6 million) - and potentially up to 16 million - through a stock market listing in London.

The plan shows increased interest in badly needed new antibiotics that are seen as essential to counter the spread of "superbug" bacteria.

Companies have for many years been reluctant to invest because of poor returns, but recently the promise of improved incentives has started to change the mood as demonstrated most vividly by Merck & Co's decision to acquire Cubist for $9.5 billion in December.

Motif Bio said it was in talks with investors ahead its move to list on the AIM market as it seeks funding to advance its experimental drugs.

If it raises the full 16 million pounds, either at or after flotation, the business is expected to be worth 45-60 million pounds.

The company said its most advanced drug candidate, iclaprim, was expected to move into advanced Phase III trials in the second half of this year and could be ready for commercialisation within three years.

It is also working on several earlier-stage drugs.

Motif Bio, which is led by former Merck executive and one-time vet Graham Lumsden, is buying rights to iclaprim through the purchase of U.S. firm Nuprim in a deal that will be completed once the company lists on AIM.

Iclaprim was previously submitted to U.S. regulators but turned down in 2009. Motif Bio believes it can get the drug approved by addressing certain shortfalls in the original development programme.

($1 = 0.6638 pounds) (Reporting by Ben Hirschler; editing by Jason Neely)