The study is published in Emerging Infectious Diseases. It suggests that these ointments may be one of the factors behind the spread of an especially severe MRSA strain, called USA300, around the world.
It also means that antibiotic ointments probably wouldn't treat or prevent MRSA skin infection, though experts say they've never been recommended for that purpose.
A spokeswoman for the drug company that makes Neosporin and Polysporin says the study doesn't prove a link between the ointments and MRSA resistance to antibiotics.
MRSA stands for methicillin-resistant Staphylococcus aureus. The majority of MRSA infections are picked up in hospitals. But they are becoming more common in the community. MRSA bacteria are spread through skin-to-skin contact and often strike people who are prone to cuts and scrapes like children and athletes.
The infections may first be mistaken for a pimple. But they can quickly worsen into deep pus-filled sores. Such infections, if not promptly treated, can spread to the blood, lungs, and other organs and may become life-threatening.
Tracking Antibiotic Resistance
The study tested 259 samples of MRSA bacteria that caused human infections treated at two hospitals in Japan.
Nineteen of the samples were USA300, a strain that is frequently found the U.S. but is rare in Japan. Scientists are worried about USA300 because it has features that make it especially dangerous.
In addition to being resistant to a host of antibiotics, for example, it makes a toxin that's responsible for its "flesh-eating" ability. It can also block the body's ability make to infection-fighting white blood cells. And USA300 appears to be replacing other, less severe MRSA strains as a cause of serious infections.
A study presented in June at the European Congress of Clinical Microbiology and Infectious Diseases in Milan, Italy, for example, found that while hospitalizations for MRSA infections in the U.S. increased only moderately between 2004 and 2008, hospitalizations related to USA300 strains more than tripled during that same period. Researchers grew all the MRSA samples on gel food in petri dishes alongside paper disks that were saturated with the antibiotics bacitracin and neomycin.
Bacitracin is among the active ingredients in Neosporin and Polysporin ointments and generic versions of those products. Neomycin is an active ingredient in Neosporin ointment.
Nearly half of the USA300 samples grew unhampered by the antibiotics bacitracin and neomycin, indicating that they were resistant to those drugs. Another USA300 sample was resistant to bacitracin, but susceptible to neomycin.
In contrast, none of the 240 samples of other MRSA strains found in Japan were resistant to bacitracin, though more than half of the other strains demonstrated at least partial resistance to neomycin.
"I think this indicates that spreading of USA300 may be related with problems in North America, specifically," says study researcher Yoshitsugu Iinuma, MD, PhD, professor in the department of infectious diseases at Kanazawa Medical University in Ishikawa, Japan, in an email. Iinuma notes that antibiotic ointment is rarely used in countries outside North America.
Johnson & Johnson, the manufacturer of Neosporin and Polysporin, say the researchers haven't proven a connection between the use of the ointments and resistance to the antibiotics in them.
"This small study did not evaluate any relationship between development of resistance to bacteria and the usage of over the counter antibiotic ointments for the prevention of infection and the authors themselves convey that further research would be needed to reach any significant conclusions," says Jodie Wertheim, a spokeswoman for the company, in an email. "It should also be noted that antibiotic ointments have been used safely for years to provide a broad-spectrum of protection against a wide variety of germs."
More Study Needed
Experts who reviewed the study say that while its findings are intriguing, they need to be duplicated on a larger scale before any firm conclusions can be made about the role of antibiotic ointments in MRSA spread or resistance.
"This study is a first step to saying 'Hey, there may be a real problem here,'" says Lance Price, PhD, associate professor of pathogen genomics at the Translational Genomics Research Institute in Flagstaff, Ariz. "So now we need to do a multi-nation study to really look at this."
But he says it makes sense to use caution with any kind of antibiotics.
"You know, if you use antibiotics routinely, you're going to end up with resistance," Price tells WebMD. "We've really got to be careful."
Other experts agree.
"I think this is an interesting paper. It brings up an important issue," says David T. Bearden, PharmD, a clinical associate professor and chair of the department of pharmacy practice at Oregon Health and Science University in Portland.
"We don't really know very much about topical products, how to use them, when to use them, what resistance means or what this does to further change [bacterial] resistance patterns," says Bearden, who was not involved in the research.
Other experts said that the study had weaknesses that could make its findings less reliable.
Suzanne F. Bradley, MD, professor of internal medicine and an infectious disease specialist at the University of Michigan Health System in Ann Arbor, says one concern is that nine of the USA300 samples came from a single outbreak. That makes it more likely, she says, that they are genetically identical and were simply passed around in the community.
Additionally, she says, the researchers give no details about the patients who had these strains, so it's impossible to know if they personally used antibiotic ointments or came from countries where they are more common.
Bradley also says the researchers offered little evidence to prove their assertion that antibiotic ointment is widely used in the U.S. but not in other countries.
Advice to Consumers
Until more is known, it's tough to know what to do about antibiotic ointment, which is a staple in many first-aid kits.
If antibiotic resistance is a concern, petroleum jelly, like Vaseline, might work just as well, says Patrick S. Romano, MD, professor of medicine and pediatrics at the University of California at Davis.
"The primary effect of the ointment is probably to act as a physical barrier to bacterial entry and as a moisturizer," Romano says in an email. Cuts and scrapes that are kept moist heal faster, he says.
"Petroleum jelly would probably work just as well for this purpose," he says, without causing resistance.