This "re-equipping and re-emergence" of a clone that caused a pandemic 40-50 years ago could mean that community acquired MRSA will spread faster and be more widespread than previously expected, warns an international team of researchers who have been studying the bacteria.
First isolated in Australia and Canada in 1953, type 80/81 penicillin-resistant Staphylococcus aureus bacteria caused skin lesions, sepsis and pneumonia in children and young adults around the world. This pandemic of both hospital and community acquired infections waned throughout the 1960s as the antibiotic meticillin was used to treat these infections.
Now researchers have shown that one of the key clones of community acquired MRSA (CA-MRSA) - infections picked up in public places which are resistant to treatment by powerful meticillin antibiotics - may have evolved from this earlier pandemic-causing strain.
The researchers have sequenced key genes from 80/81 samples isolated between 1955 and 1969 in Australia, England and the USA, and compared them with the same regions in genes from a clone of one of the most common CA MRSAs which has been found in England and Scotland.
They found that these key regions in nearly all of the 80/81 isolates were identical to the CA-MRSA clone, and also that they share the same highly-virulent toxin, called Panton-Valentine leucocidin.
They believe that their findings suggest that this particular CA MRSA clone has evolved from the earlier 80/81 type, developing resistance to meticillin antibiotics over the last 30-40 years, possibly through several intermediate steps.
"At the time of the 1950s pandemic, many doctors thought that these isolates were unusually transmissible and virulent," said Dr Mark Enright from Department of Biology and Biochemistry the University of Bath (UK) who is leading the research.
"We have shown that 80/81 and its souped-up community acquired MRSA descendent share many of the same features, which explains why 1950s pandemic was so successful, but also shows why community acquired MRSA could pose such a serious public health challenge in coming years.
"The community acquired MRSA clone has a toxin and other traits with a proven track record for causing serious diseases in healthier and younger age groups than those currently regarded as at risk. The increased resistance to antibiotics of the community acquired MRSA clone over its 80/81 ancestor mean that there could also be other factors which complicate the treatment of the disease it causes."