Swiss drugmaker Roche will pay up to 500 million Swiss francs ($548 million) for an experimental antibiotic, marking a rare foray by a major pharmaceutical firm into the battle against so-called "superbug" infections found in hospitals.

The World Health Organisation has warned of the growing public health threat from drug-resistant superbugs. There are 25,000 deaths each year in the European Union alone due to antimicrobial resistance, Roche said on Monday.

However, the problem is not yet widespread enough to attract major investment by most top pharmaceutical companies, with many of them in fact cutting back research into antibiotics.

Pfizer, once the leader in the field, closed its antibiotic R&D centre in Connecticut in 2011, while Bristol-Myers Squibb and Eli Lilly have also cut back, leaving few big firms in the game.

Roche said it had signed an exclusive global licensing deal to develop and commercialise privately held Polyphor's investigational antibiotic POL7080 against certain superbug infections found in hospitals.

Under the deal, Roche will make an upfront payment of 35 million Swiss francs and milestone payments of up to 465 million.

In addition, Polyphor will be entitled to tiered, double-digit percentage royalties on any product sales and will retain the option to co-promote an inhaled formulation of POL7080 in Europe, Roche said.

POL7080 belongs to a new class of antibiotics that kills Pseudomonas aeruginosa, a bacterium found in hospitals and resistant to many antibiotic treatments, by a novel mode of action, the Swiss group added.

It has demonstrated clinical safety and tolerability in a Phase I clinical trial and holds promise for the treatment of serious and often life-threatening bacterial infections caused by multi-drug resistant Pseudomonas species, Roche said.

Pseudomonas aeruginosa, which accounts for one in every 10 hospital-acquired infections in the United States, can cause death in around 50 percent of patients with weakened immune systems, such as those suffering from cancer, AIDS or chronic infections like cystic fibrosis. – Reuters