Three premature babies have died in a clinic in northern Germany, after being infected with bacteria resistant to antibiotics, authorities announced Wednesday.

Two children died in October and the other in August in Bremen.

Fifteen other babies have been infected with the unidentified bacteria but it did not pose a threat in most of the infants, said Karla Goetz, a spokesperson for the Bremen city-state .

The clinic has closed its neonatal unit as a precaution while the Robert-Koch Institute, which deals with health protection, investigates the source of the bacteria.