Repeated exposure to triclosan reduces virulence in S. aureus

June 21, 2012

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

Pneumonia vaccine under development provides 'most comprehensive coverage' to date, alleviates antimicrobial concerns

October 20, 2017
In 2004, pneumonia killed more than 2 million children worldwide, according to the World Health Organization. By 2015, the number was less than 1 million.

Newly discovered viral marker could help predict flu severity in infected patients

October 20, 2017
Flu viruses contain defective genetic material that may activate the immune system in infected patients, and new research published in PLOS Pathogens suggests that lower levels of these molecules could increase flu severity.

H7N9 influenza is both lethal and transmissible in animal model for flu

October 19, 2017
In 2013, an influenza virus that had never before been detected began circulating among poultry in China. It caused several waves of human infection and in late 2016, the number of people to become sick from the H7N9 virus ...

Flu simulations suggest pandemics more likely in spring, early summer

October 19, 2017
New statistical simulations suggest that Northern Hemisphere flu pandemics are most likely to emerge in late spring or early summer at the tail end of the normal flu season, according to a new study published in PLOS Computational ...

New insights into herpes virus could inform vaccine development

October 18, 2017
A team of scientists has discovered new insights into the mechanisms of Epstein-Barr virus (EBV) infection, as well as two antibodies that block the virus' entry into cells. The findings, published in Proceedings of the National ...

Pair of discoveries illuminate new paths to flu and anthrax treatments

October 17, 2017
Two recent studies led by biologists at the University of California San Diego have set the research groundwork for new avenues to treat influenza and anthrax poisoning.

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.