Disinfectant could increase antibiotic resistance of bug

Tue, Dec 29, 2009, 00:00

USING A PARTICULAR disinfectant could render a potentially dangerous hospital bug more resistant to both the disinfectant itself and in turn to antibiotic treatment, suggests new research from NUI Galway.

The study, published in the current (January) edition of the journal Microbiology, looked at the effects of exposing Pseudomonas aeruginosabacteria grown in the lab to increasing concentrations of a certain type of biocide, or disinfectant.

The bacterium occurs widely in soil and water, but also occurs in healthcare settings where it can pose problems for patients with vulnerable immune systems, including those hospitalised with severe burns or cancer, premature babies and people with cystic fibrosis.

In clinical settings, disinfectants are used to limit the spread of potentially dangerous bacteria on surfaces, but if a patient still becomes infected then antibiotics may be used to help treat that infection.

The study investigated the link between adaptation both to disinfectants and to antibiotics in Pseudomonas aeruginosacultures. When researchers exposed the Pseudomonasbacteria in the lab to increasing concentrations of the disinfecting agent benzalkonium chloride (BKC), a variant of the bacterium developed that was 12-fold less sensitive to the disinfectant.

That same variant also showed a 256-fold increase in resistance to the antibiotic ciprofloxacin, even though the bacteria had never been previously exposed to the antibiotic.

The research showed that the resistant Pseudomonasbacteria could more efficiently pump out antimicrobial agents from the bacterial cell, and the variants also had a mutation in their DNA that allowed them to resist ciprofloxacin-type antibiotics.

“It is clear from the present study that the presence of subinhibitory concentrations of BKC is sufficient to select for adapted variants of Pseudomonas aeruginosain a sensitive culture,” wrote the study authors.

Lead researcher Dr Ger Fleming commented on the finding that low, non-lethal concentrations of disinfectant were associated with increased antibiotic resistance.

“In principle, this means that residue from incorrectly diluted disinfectants left on hospital surfaces could promote the growth of antibiotic-resistant bacteria,” he said.

“What is more worrying is that bacteria seem to be able to adapt to resist antibiotics without even being exposed to them.”

Dr Fleming also highlighted the need to further study 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,” he said. “This will increase the effectiveness of both our first and second lines of defence against hospital-acquired infections.”