New types of MRSA have been identified that attack the immune system, are highly infectious and can kill patients by destroying lung tissue.
And the bacteria are spread through the community and are not strictly confined to hospitals like most strains of the superbug.
They produce a toxin called Panton-Valentine leucocidin (PVL) that kills white blood cells, which are an essential part of the body's immune system defences.
Experts are warning that people who are infected with the strains may not be diagnosed straight away because the initial symptoms appear relatively harmless.
By the time a correct diagnosis is made it might be too late to save the patient, delegates at the Federation of Infection Societies Conference at the University of Cardiff were told.
Dr Marina Morgan, from the Royal Devon & Exeter Foundation NHS Trust, said: "The new community-associated MRSA strains appear to be more virulent and more easily spread between people.
"These community-associated versions have been found in people with few, if any, reasons to have MRSA. Typically they haven't recently been in hospital, or are not looking after or living with people with MRSA."
Already a major problem in hospitals, MRSA is now starting to spread to the wider population. Community MRSA is now well established in America, where it is a major cause of childhood infection.
And doctors are concerned that the same pattern may now be repeated in Britain.