Antimicrobial Activity of Nonantibiotics in Topical Acne Treatments

acne, acne treatment
The antimicrobial activity of nonantibiotic acne agents may provide protection against a background of increased drug-resistant bacteria.

According to in vitro study data published in Science Report, nonantibiotic acne treatment agents had modest antimicrobial effects against antibiotic-resistant bacteria strains. Antibiotic agents, in contrast, had significantly reduced effects against resistant bacteria. Thus, nonantibiotic acne treatments may be a preferred alternative to prescribed antibiotics in efforts to reduce antibiotic resistance.  

Investigators conducted a comparative analysis of common topical acne drugs against the primary etiologic agent for acne: Cutibacterium acnes. In addition, standard aerobic and anaerobic minimum inhibitory concentration (MIC) assays were used to test the activity of antibiotics and other topical agents against a series of antibiotic-sensitive and antibiotic-resistant bacteria strains. Bacteria were selected based on data from prior microbiome studies. Bacteria known to be involved in skin infections were also tested, including Streptococci, Bacilli, Enterococci, Micrococci, Escherichia coli and Acinetobacter johnsonii.

Topical antibiotics tetracycline, erythromycin, oxacillin, and clindamycin displayed potent activity against a range of bacteria under anaerobic and aerobic conditions. However, erythromycin, oxacillin, and clindamycin lost activity against drug-resistant bacteria, including methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant Staphylococcus  pneumoniae. Dapsone had lower potency compared with other antibiotics but had wider-ranging activity against resistant strains. The nonantibiotic topical treatments — including salicylic acid, azelaic acid, and benzoyl peroxide — maintained activity against all resistant bacteria tested, including S aureus, S epidermidis, and S pneumoniae. The potency of these drugs was approximately 1000-fold less active than the antibiotic drugs, ranging from 2000 to 64,000 μg/mL. Even so, topical drugs are typically applied at concentrations 20-fold higher than antibiotics, increasing the likelihood of antimicrobial activity even with reduced potency.

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The antimicrobial activity of these nonantibiotic topical medications warrants further research to combat the rise of antibiotic resistance. “The retention of high levels of antimicrobial activity by salicylic acid, azelaic acid, and benzoyl peroxide against antibiotic-resistant strains of bacteria suggests that these treatments could be useful alternatives to antibiotic-based therapies in the case of resistant bacteria,” investigators wrote.

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Blaskovich MAT, Elliott AG, Kavanagh AM, Ramu S, Cooper MA. In vitro antimicrobial activity of acne drugs against skin-associated bacteria [published online October 10, 2019]. Sci Rep. doi:10.1038/s41598-019-50746-4