Repeated exposure to triclosan reduces virulence in S. aureus

June 21, 2012, American Society for Microbiology

Repeated laboratory exposures to triclosan reduced susceptibility to antibiotics in Staphylococcus aureus, but probably not sufficiently to render commonly used antibiotics ineffective, according to a paper in the June 2012 issue of the journal Antimicrobial Agents and Chemotherapy. It also generated less virulent, less fit “small colony variants” of the pathogen.

The research is important, because concern has arisen that antiseptics and disinfectants might cause bacteria to develop reduced susceptibility to these compounds, as well as to , to the point where for some uses, in some countries, they have been strictly regulated, says principal investigator Andrew McBain, of the University of Manchester, UK. S. aureus is an important source of hospital- and community-acquired infections. Triclosan is a broad-spectrum antibacterial and antifungal compound often used in cleaning supplies, personal care products, toys, and other consumer products, as well as in clinical settings, for example, to reduce methicillin-resistant S. aureus infections.

The research began serendipitously when, during an unrelated study, Sarah Forbes, a PhD student in McBain’s lab, created a population of small colony variants by serially exposing S. aureus ten times on concentration gradients of triclosan. “This type of selection system we used represents a worst case scenario in terms of altering bacterial susceptibility because of the repeated and continuously elevating high level exposure,” says McBain. “We then grew this strain a further ten times on triclosan-free medium to see if it could recover.” The exposed strain had reduced susceptibility to triclosan, and it was defective in its ability to form biofilms, as well as in a few other virulence-related functions. “We therefore hypothesized that if virulence had been altered at all in our strain, it had actually been reduced,” he says.

Forbes, and postdoctoral research associate Joe Latimer then grew the small colony variant, as well as the unexposed strain of S. aureus, in the wax moth larvae model, Galleria mellonella, “and found that our small colony variants were indeed less pathogenic in this test system than the unexposed strain,” says McBain. Even after it was grown another ten times in triclosan-free media, the small colony variant failed to fully regain its virulence, as well as its normal ability to form biofilms and to produce the enzyme, DNase.

“The work suggests that at least for small colony variants, long-term exposure can select for reduced susceptibility, but that the resulting organisms may also be reduced in their pathogenic capability, or fitness,” says McBain. He adds that “even though our small colony variants were less susceptible, their resistance levels remained markedly lower than commonly used concentrations so they were still probably effectively treatable.”

Explore further: Antibiotics boost risk of infection with antifungal-resistant candida

More information: J. Latimer, S. Forbes, and A.J. McBain, 2012. Attenuated virulence and biofilm formation in Staphylococcus aureus following sublethal exposure to triclosan. Antim. Agents Chemother. 56:3092-3100.

Related Stories

Antibiotics boost risk of infection with antifungal-resistant candida

May 22, 2012
Previous exposure to certain antibiotics could boost the risk of infection with drug-resistant strains of a severe fungal infection. Researchers report their findings in the May 2012 issue of the journal Antimicrobial Agents ...

Compound in Apples Inhibits E. coli O157:H7

December 16, 2011
A compound that is abundant in apples and strawberries inhibits the highly pathogenic E. coli O157:H7 biofilms while sparing a beneficial strain of E. coli that also forms biofilms in the human gut, according to a paper in ...

Garlic constituent blocks biofilm formation, could benefit CF patients and others

May 22, 2012
E Pluribus Unum, the motto of the United States, could just as well apply to biofilm-forming bacteria. Bacterial biofilms are far more resistant than individual bacteria to the armories of antibiotics we have devised to combat ...

Antibacterials in personal-care products linked to allergy risk in children

June 19, 2012
(Medical Xpress) -- Exposure to common antibacterial chemicals and preservatives found in soap, toothpaste, mouthwash and other personal-care products may make children more prone to a wide range of food and environmental ...

Recommended for you

Leprosy's drug resistance and origin revealed by genome analysis

January 24, 2018
Leprosy is an infectious disease with gruesome symptoms. It damages the skin, peripheral nerves, the upper respiratory tract, and the eyes. Despite being curable with multidrug therapy, leprosy still persists in many developing ...

Nanoparticle vaccine offers universal protection against influenza A viruses, study finds

January 24, 2018
Researchers have developed a universal vaccine to combat influenza A viruses that produces long-lasting immunity in mice and protects them against the limitations of seasonal flu vaccines, according to a study led by Georgia ...

A new theory on reducing cardiovascular disease risk in binge drinkers

January 23, 2018
A new study shows that binge drinkers have increased levels of a biomarker molecule—microRNA-21—that may contribute to poor vascular function.

Flu infection study increases understanding of natural immunity

January 23, 2018
People with higher levels of antibodies against the stem portion of the influenza virus hemagglutinin (HA) protein have less viral shedding when they get the flu, but do not have fewer or less severe signs of illness, according ...

New long-acting approach for malaria therapy developed

January 22, 2018
A new study, published in Nature Communications, conducted by the University of Liverpool and the Johns Hopkins University School of Medicine highlights a new 'long acting' medicine for the prevention of malaria.

Virus shown to be likely cause of mystery polio-like illness

January 22, 2018
A major review by UNSW researchers has identified strong evidence that a virus called Enterovirus D68 is the cause of a mystery polio-like illness that has paralysed children in the US, Canada and Europe.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.