Mysteriously, a Huge Study Finds a Drop in Antibiotic Resistant (MRSA) Infections

For once there is good news — surprising news, but good news — in the fight against antibiotic-resistant organisms. A recent study found that Staphylococcus aureus bacteria is becoming more sensitive to some key drugs used to treat it.

Helio S. Sader, Senior Director at JMI Laboratories, presented his findings on June 4 at the ASM Microbe conference in New Orleans, Louisiana.

Sader's study examined nearly 20,000 Staphylococcus aureus infections in patients hospitalized in medical facilities in 30 states between 2009 and 2015. One of their key findings was that rates of Staphylococcus aureus infections that were resistant to methicillin treatment — a virulent and hard-to-treat infection called MRSA — decreased during that period.

"Results showed that S. aureus' rates of resistance to certain antibiotics decreased over time, which isn't often seen," Sader said in a press release.

Methicillin-Resistant Staph Aureus — MRSA

MRSA is more deadly than other staph bacteria, party because it produces enzymes that enable it to invade and destroy host tissues and help it travel to other sites. Rampant MRSA infections can require limb amputations to prevent it from moving to other parts of the body.

Mysteriously, a Huge Study Finds a Drop in Antibiotic Resistant (MRSA) Infections — *Image via CDC*

The most common types of methicillin-resistant Staphylococcus aureus infections in the community are skin wounds, and occasionally, pneumonia. In healthcare settings, MRSA is more apt to invade the bloodstream, like at surgical sites, and bloodstream infections are the deadliest. Blood infections with MRSA are the deadliest — about 31% of those patients die.

The high death rate associated with MRSA bloodstream infections and its antibiotic resistance earned it a place on the Centers for Disease Control list of Serious Threats to global health.

The Not-So-Resistant MRSA

Between 2009 and 2015, the researchers studied 19,036 Staphylococcus aureus infections in the US, half of which were skin infections, about 22% were respiratory infections, and 20% were bloodstream infections. The study found that in 2009, 47.2% of these infections were resistant to methicillin, but that rate dropped to 43.6% in 2015, then dropped again, to 42.2% in 2016.

In contrast, MRSA also became less resistant to another antibiotic, clindamycin, during the study period. It worked on 64.4% of the MRSA infections in 2009, but that increased to 71.8% in 2015.

Luckily, methicillin isn't the only drug we can use to treat S. aureus infections. An antibiotic called Ceftaroline was approved for use in patients in October 2010, and can kill various strains of Staphylococcus aureus, including MRSA.

The researchers found that Ceftaroline inhibited 97.0% of the Staphylococcus aureus bacteria tested in the study, including all of the MRSA infections. Daptomycin, linezolid, tigecycline, vancomycin, and trimethoprim-sulfamethoxazole were also very active against MRSA with and the sensitivity rates remained pretty constant throughout the study period. That's good news since at least these infections aren't becoming more resistant to these other drugs.

Taken together, the results show that the rate of Staphylococcus aureus infections that are resistant to methicillin and clindamycin are dropping — opening up two treatment options in some patients that weren't there in 2009.

What Does It Mean?

A review commissioned by the UK Prime Minister predicted that 10 million people a year will die from antibiotic resistant infections by 2050.

The reason for the decline in rates of MRSA found by the study may be due to fewer infections with Staphylococcus aureus that is methicillin resistant (potentially to better hygienic practices) or to a change in the overall sensitivity of Staphylococcus aureus that made it more sensitive to methicillin. Whatever the reason, it is unexpectedly good news. It means more patients' infections may be able to be successfully treated and fewer patients may die.

For now, we can enjoy the bit of optimistic news. Whatever the cause of the findings, maybe we aren't doomed to the fate predicted for us.