Possible Treatment For All MRSA Strains 020113
February 1, 2013

Study Seeks Treatment For All MRSA Strains In Genetic Vulnerabilities

Connie K. Ho for redOrbit.com — Your Universe Online

A new study by researchers from the University of North Carolina (UNC) may be able to help develop treatments that work against all MRSA strains, according to an article recently published in the journal Cell Host & Microbe.

According to the Mayo Clinic, methicillin-resistant Staphyloccoccus aureus (MRSA) infections can be found in people who stay in hospitals, nursing homes, dialysis centers or other healthcare settings. MRSA is a type of bacteria that is difficult to treat due to its resistance to antibiotics such as penicillins or cephalosporins. Another form of MRSA known as community-associated MRSA (CA-MRSA) occur among healthy individuals who have not recently been hospitalized and often begins as a painful skin boil. It is spread by skin-to-skin contact and those who are at risk for this form of MRSA often include child care workers, young people who play contact sports such as wrestling, and people who live in crowded areas.

The recent study focuses on a new strain of MRSA called USA300 that has appeared in the last 10 years. The strain has the ability to spread past hospital walls and individuals have a higher of risk of contracting the harmful bacterial infection. USA300 is unique in that it has a group of genes that are not shared by other strains of MRSA. During their study, scientists from the UNC School of Medicine found the gene that allows the infection to remain on the skin longer than other strains, making it easier to pass the infection on to other individuals.

"The problem is by the time you figure out how one strain comes into dominance, it often fades away and a new strain comes in. But because these compounds occur naturally and are so toxic, we still think they can lead to treatments that are effective against all MRSA. We will just have to put in a little extra work to block the gene and make this particular strain of MRSA susceptible to polyamines," explained the study´s senior author Anthony Richardson, Assistant Professor of Microbiology and Immunology, in a statement.

The researchers believe that the gene also causes this strain of MRSA to be resistant to polyamines, compounds that occur naturally on human skin and are typically toxic to other strains. The findings of this particular gene provided the researchers with additional information to develop new treatments against MRSA, including the USA300 strain that is found in the majority of hospital visits related to MRSA skin and soft tissue infections.

For their research, the team of investigators was able to track an attribute of MRSA that had not previously been studied and were able to better understand why MRSA is so sensitive to polyamines. Polyamines play an important role in wound care as they are anti-inflammatory and aid in tissue regeneration.

The scientists tested hundreds of MRSA strains and found that all except for the USA300 strain were sensitive to polyamines. They also discovered that this specific MRSA strains had a group of 34 genes, known as the arginine catabolic mobile element (ACME), which were not found in other strains.

Following the discovery of the ACME, the scientists mutated each of the genes so that they could change the gene sequence and create a new strain that could be eliminated by the polyamines. The researchers then added a normal, non-mutated version of the gene called SpeG to the other strains of MRSA to verify that those strains had become resistant to polyamines. The goal of the researcher was to determine exactly which gene was preventing the bacteria from being killed by the toxic polyamines so that they could focus on that particular gene when possibly developing a treatment in the future.

In the last step of the study, the researchers utilized mouse models of MRSA infection to study whether the gene had the same effect in an environment with a real infection. They demonstrated that the presence of non-mutated SpeG gene was important in helping the USA300 strain stay in the skin for a long period of time.

"Previously, the field tried to understand MRSA by focusing on attributes that we already knew were important, such as the amount of toxins or virulence factors a given strain makes. Those elements may explain why the disease is so bad when you get it, but they don't explain how a particular strain takes over. Our work uncovers the molecular explanation for one strain's rapid and efficient spread to people outside of a crowded hospital setting," concluded Richardson in the statement.

If you would like to learn more, the U.S. Centers for Disease Control and Prevention (CDC) provides online resources about MRSA infections, including how to identify, prevent and treat infections.