Researchers at the University of California, San Francisco, said the bacteria appear to be transmitted most easily through intimate sexual contact, but can spread through casual skin-to-skin contact or via contaminated surfaces.

The newly discovered strain of bacteria is closely related to MRSA bacteria found in hospitals and the community, but resists many more front-line antibiotics.

Both strains are technically known as MRSA USA300, but the new strain spreads easily through skin-to-skin contact, invading skin and tissue beneath the skin, the researchers said.

"These multi-drug resistant infections often affect gay men at body sites in which skin-to-skin contact occurs during sexual activities," lead author Binh Diep said in a statement. "But because the bacteria can be spread by more casual contact, we are also very concerned about a potential spread of this strain into the general population."

However, a good scrubbing with soap and water may be the most effective way to prevent transmission of this bacteria -- especially after sex, Diep said.

The findings are published online ahead of print in the Annals of Internal Medicine.