A New Look into How Disinfectant Products Contribute to Antibiotic Resistance

We know that the virulence of drug-resistant superbugs has been bolstered by their exposure to antibiotic medications, and now a new study conducted by researchers in the United Kingdom has found evidence that bacteria are also building resistance from exposure to disinfectant products.

Earlier this year, the US Food and Drug Administration ruled that companies in the United States selling over-the-counter antiseptic hand soap would no longer be able to market their products as antibacterial, after manufacturers failed to prove that these products are more effective than hand soap at preventing illness. The ruling came as more evidence also showed that antibacterial household products were helping to fuel the growing strength and resistance of pathogenic bacteria, thus, doing more harm than good. The Centers for the Disease Control and Prevention (CDC) attributes much of the increasing rate of bacterial infections impervious to antibiotic treatment to our overuse of the drugs in human health as well as in the livestock and the agriculture sector. In addition, researchers have also been looking into other contributing factors of resistance.

Recently, a team of researchers from Public Health England’s National Infection Service investigated the effects of the disinfectant product ingredient chlorhexidine on Klebsiella pneumoniae. Today, the pathogen is one of many responsible for causing healthcare-associated infections, of which there were about 722,000 in the United States in 2011, with an estimated 75,000 deaths occurring in hospitalized patients suffering with such infections. K. pneumoniae, when spread in hospitals and healthcare settings, are known to cause pneumonia, bloodstream infections, wound or surgical site infections, and meningitis, and have increasingly developed resistance to the antibiotic carbapenem. The researchers had previously found that K. pneumoniae bacterium are able to adapt and become more resistant when exposed to disinfectant.

In their new investigation, published in the journal Antimicrobial Agents and Chemotherapy from the American Society for Microbiology, the study team found that five of the six strains of K. pneumoniae not only survived increased exposure to the disinfectant chemical chlorhexidine, but, in turn, developed resistance to the disinfectant as well as to the antibiotic colistin. The researchers conducted the study in part due to the uncommon but observed phenomenon of pathogens developing what is known as cross-resistance to both disinfectant agents and antibiotic medications. Antiseptic products containing the active ingredient are commonly used in both households and hospitals, and the current study exposed six strains to chlorhexidine increasing concentrations of the disinfectant. Some isolates did not survive under the high exposure to chlorhexidine, but according to the study, after exposure, five of the six strains saw an increase in their minimum inhibitory concentrations (MIC) to colistin, the lowest concentration at which the antibiotic was able to inhibit the growth of the pathogen. MIC values for colistin increased from 2-4 150 mg/L to more than 64 mg/L in the newly-resistant K. pneumoniae isolates, showing a marked level of immunity to the antibiotic.

“Chlorhexidine is a critical part of current infection control practices, and the development of increased resistance to this compound has potential implications for our ability to prevent infections during routine and emergency surgery, and during admission to hospitals,” said J. Mark Sutton, PhD, one of the study’s coauthors, in a press release about their findings. As a last-line antibiotic, colistin is regarded as a lifeline for some of the hardest to treat infections, so the rare but increasing occurrence of pathogens resistant to colistin is a troubling development for the healthcare system. “If the same response is seen in hospitals, this might mean that we need to rethink how and where some types of critical disinfectants or antiseptics are used in the clinic,” Dr. Sutton added.

Hand hygiene and infection control precautions made by healthcare workers remain an important line of defense for preventing the spread of K. pneumoniae in hospitals. The CDC also recommend that patients practice hand washing and hygiene very often, including:

• Before preparing or eating food
• Before touching their eyes, nose, or mouth
• Before and after changing wound dressings or bandages
• After using the restroom
• After blowing their nose, coughing, or sneezing
• After touching hospital surfaces such as bed rails, bedside tables, doorknobs, remote controls, or the phone