A disinfectant commonly used in hospitals can cause bacteria to
become resistant not only to the disinfectant but also to
antibiotics, a study by Irish researchers has found.
Antibiotic-resistant bacteria are a constant concern in
hospitals. The research, published in the journal Microbiology,
indicates hospitals may have to re-evaluate their disinfecting
Even small amounts of the disinfectant benzalkonium chloride may
promote the evolution of resistant strains of the "opportunistic"
bacterium Pseudomonas aeruginosa, the study found. The bacterium
attacks people with weakened immune systems, as well as those with
Pseudomonas cultures exposed to the disinfectant developed
mutant strains that were 256 times more resistant to
ciprofloxacin-class antibiotics, according to the study, led by Dr.
Gerard Fleming of the National University of Ireland in Galway.
The Pseudomonas bacteria mutated to form a "pump" that removed
both the disinfectant and antibiotics, and also developed a second
mutation that gave them resistance to the antibiotics.
Antibiotic resistance has been documented for decades, but it
was not considered a major problem until fairly recently. As more
bacteria evolve resistance to more kinds of antibiotics, infections
have re-emerged as a growing threat to public health.
The resistance develops according to Darwinian principles of
natural selection. When bacteria encounter antibiotics, those that
spontaneously develop mutations that help them resist antibiotics
prevail over vulnerable bacteria.
In addition, bacteria directly exchange genetic material in a
microbial form of sex. This allows the beneficial mutations (for
the bacteria) to spread to other bacteria, even different
To stop the spread of bacteria, hospitals employ disinfectants
and antibiotics. Disinfectants directly kill microbes; antibiotics
inhibit their growth, and may also kill the bacteria. Hospitals
apply disinfectants to surfaces to eliminate disease-causing
bacteria in the environment. Doctors give antibiotics to patients
to stop infections.
The finding that disinfectant resistance encourages antibiotic
resistance means hospitals should consider their effects in tandem,
Fleming said in a news release on the study.
"In principle, this means that residue from incorrectly diluted
disinfectants left on hospital surfaces could promote the growth of
antibiotic-resistant bacteria," Fleming said. "What is more
worrying is that bacteria seem to be able to adapt to resist
antibiotics without even being exposed to them."
Call staff writer Bradley J. Fikes at 760-739-6641. Read his
blogs at bizblogs.nctimes.com.