EU flags fly outside the European Commission headquarters in Brussels, during gas talks between the EU, Russia and Ukraine on Oct. 30, 2014. Francois Lenoir/Reuters LONDON (Reuters) - More and more infections in Europe are proving able to evade even the most powerful, last-resort antibiotics, posing an alarming threat to patient safety in the region, health officials said on Monday.

Releasing annual data on antibiotic resistant superbugs, the European Center for Disease Prevention and Control (ECDC) said bacterial infections resistant to carbapenems -- a major last-line class of antibiotics used to treat hospital-acquired superbugs -- are ever more common in the European Union.

"With a smaller number of effective antibiotics, we are gradually returning to the 'pre-antibiotic era' when bacterial diseases could not be treated and most patients would die from their infection," said Marc Sprenger, the ECDC's director.

The Stockholm-based ECDC also said it had for the first time collected data on resistance among infections caused by a bacteria called Klebsiella pneumoniae to a powerful but older antibiotic known as colistin -- and had found alarming signs.

"According to our data, resistance to colistin was observed in 5 percent of Klebsiella pneumoniae isolates for the EU overall," Sprenger said.

Klebsiella pneumoniae is a common cause of pneumonia, urinary tract and bloodstream infections in hospital patients. If antibiotics are unable to treat them effectively, patients can face long, costly stays in hospital, and risk dying.

Colistin is a last-resort antibiotic developed several decades ago that has serious side-effects and limitations to its use, but has become essential for treating carbapenem-resistant Klebsiella pneumoniae infections.

Drug resistance is driven by the misuse and overuse of antibiotics, which encourages bacteria to evolve to survive and develop new ways of beating the drugs.

It has been a feature of medicine since Alexander Fleming's discovery of penicillin in 1928, but has become a major global health threat as new drug development has failed to keep pace with the bugs' ability to develop resistance to them.

The ECDC data showed an increase of carbapenem resistance in Klebsiella pneumoniae to a population-weighted EU average percentage of 8.3 percent in 2013 from 4.6 percent in 2010.

Vytenis Andriukaitis, Europe's commissioner for health and food safety, said the near doubling of resistance in some bacteria in three years was "truly alarming" and illustrated the need to tackle the issue from all directions.

"Antimicrobial resistance is one the most pressing public health issues of our time," he said in a statement as the data were published.

(Editing by Crispian Balmer)