Two Strains Of MRSA Here To Stay

both strains of MRSA here to stay

Two competing strains of Methicillin-resistant Staphylococcus aureus (MRSA), often better known as antibiotic-resistant bacteria or antibiotic-resistant staph, have existed since about the mid-1990s. Before that time, MRSA mostly affected patients in hospitals and their caregivers. That strain is called HA-MRSA.

Since then, more and more otherwise healthy people have become infected with MRSAs in intimate community settings like sports teams and daycare centers. That’s a different strain, CA-MRSA, which isn’t as resistant to as many antibiotics as its older cousin.

CA-MRSA is a much more invasive form of the disease which spreads more rapidly. Is it possible that this faster growing form of the disease could out-compete HA-MRSA?

A team from Princeton University recently published the results of their mathematical modeling of the competition in the journal PLOS Pathogens. In a nutshell, their study said that both strains are here to stay and that they will each mostly remain in the environment to which they are better adapted.

You can think of CA-MRSA as being lighter and faster on its feet. It can move more quickly through communities because it doesn’t have the burden of resistance to as many antibiotics. When it does try to gain a foothold in a hospital setting, the Princeton team found that it can be quickly wiped out by the aggressive strategies available to fight infection there.

The HA-MRSA strain may be more heavily armored, allowing it to fight back against hospital caregivers, but it simply can’t keep up with CA-MRSA out in the greater community.


If the strengths of both strains were able to somehow combine, the new MRSA would represent a human health disaster of unknown proportions.

Fortunately, the Princeton models suggested that it can’t happen. Both strains of MRSA are here to stay, and any CA-MRSA that tries to invade hospitals will be quickly dealt with.

[photo E. coli courtesy Surian Soosay and flickr]