Superbug

Superbug: An informal term for a bacterium that has become resistant to antibiotics usually used to treat it, as methicillin-resistant Staphylococcus aureus (MRSA) or any multiresistant bacterium.

"A drug-resistant superbug that spreads by skin contact is infecting thousands of people across the US and may now have reached Europe." (New Scientist March 5, 2003)