Using disinfectants could help superbug bacteria become resistant not only to the disinfectant itself but to antibiotics, even if they have not been exposed to them, according to a new study from Ireland: the findings could be important step in the fight to prevent superbugs spreading in hospitals.

The study is the work of lead author Dr Gerard Fleming from the National University of Ireland (NUI) in Galway, and colleagues, and is available to read online in the January issue of Microbiology. Fleming heads NUI's Marine Microbiology Laboratory, where as well as researching deep ocean microbes, he and his team investigate cross-resistance between biocide and antibiotics in human pathogens, and assess agricultural workers' exposure to health hazards.

One of the human pathogens Fleming and his team have been investigating is Pseudomonas aeruginosa, an opportunistic bacterium that can cause infections in people with weak immune systems, cystic fibrosis (CF), diabetes and other diseases. It is an important cause of hospital-acquired infections.

There are two ways of managing hospital-acquired infections: prevention by disinfection of surfaces in the hospital, and treatment by antibiotics: what is worrying about this study is that the bacterium appears to have developed a way to foil both these routes.

Fleming and colleagues reported how by adding more and more disinfectact to lab cultures of P. aeruginosa, they found it adapted to survive not only the disinfectant itself, but also the commonly prescribed antibiotic ciprofloxacin, even without being exposed to it.

The disinfectant they used was benzalkonium chloride (BKC), a bactericide, algaecide and fungicide contained in many hospital, livestock and personal hygiene products, from surface disinfectants to skin sanitizers and cosmetics.

Fleming and colleagues found that the adapted P. aeruginosa had a DNA mutation that allowed it specifically to resist antibiotics like ciprofloxacin and that the mutated bacterial cells had become efficient at pumping out disinfectant and antibiotic agents.

Also important, is they found that adding only very small non-lethal amounts of disinfectant to the culture, made the adapted bacteria more likely to survive than the non-adapted bacteria, which Fleming said establishes the principle that:

"Residue from incorrectly diluted disinfectants left on hospital surfaces could promote the growth of antibiotic-resistant bacteria."

However, Fleming said they were more worried about the fact that:

"Bacteria seem to be able to adapt to resist antibiotics without even being exposed to them."

He said it was also important to look at the the environmental factors that might promote antibiotic resistance:

"We need to investigate the effects of using more than one type of disinfectant on promoting antibiotic-resistant strains. This will increase the effectiveness of both our first and second lines of defence against hospital-acquired infections," said Fleming.

"Effect of subinhibitory concentrations of benzalkonium chloride on the competitiveness of Pseudomonas aeruginosa grown in continuous culture."
Paul H. Mc Cay, Alain A. Ocampo-Sosa and Gerard T. A. Fleming
Microbiology 156 (2010), 30- 38
DOI 10.1099/mic.0.029751-0

Source: Society for General Microbiology.

Written by: Catharine Paddock, PhD