Abstract
ABSTRACTMany of the most common disinfectant and sanitizer products are formulations of multiple antimicrobial compounds. Products claiming to contain synergistic formulations are common, although there is often little supporting evidence. The antimicrobial interactions of all pairwise combinations of common disinfectants (benzalkonium chloride, didecyldimethylammonium chloride, polyhexamethylene biguanide, chlorocresol, and bronopol) were classified via checkerboard assay and validated by time-kill analyses. Combinations were tested against Acinetobacter baumannii NCTC 12156, Enterococcus faecalis NCTC 13379, Klebsiella pneumoniae NCTC 13443, and Staphylococcus aureus NCTC 13143. Synergistic interactions were identified only for the combinations of chlorocresol with benzalkonium chloride and chlorocresol with polyhexamethylene biguanide. Synergism was not ubiquitously demonstrated against all species tested and was on the borderline of the synergism threshold. These data demonstrate that synergism between disinfectants is uncommon and circumstantial. Most of the antimicrobial interactions tested were characterized as additive. We suggest that this is due to the broad, nonspecific mechanisms associated with disinfectants not providing an opportunity for the combined activities of these compounds to exceed the sum of their parts.
Highlights
Many of the most common disinfectant and sanitizer products are formulations of multiple antimicrobial compounds
The central axiom that synergistic interactions can occur between antimicrobials with different mechanisms of action and target sites has resulted in the liberal use of claims of synergy when multicomponent disinfectants products are described and marketed
Chlorocresol achieved MICs of 200 mg/ml and 125 mg/ml for K. pneumoniae and A. baumannii, respectively, while the MICs for S. aureus and E. faecalis were significantly higher at 600 mg/ml and 500 mg/ml, respectively
Summary
Many of the most common disinfectant and sanitizer products are formulations of multiple antimicrobial compounds. Most of the antimicrobial interactions tested were characterized as additive We suggest that this is due to the broad, nonspecific mechanisms associated with disinfectants not providing an opportunity for the combined activities of these compounds to exceed the sum of their parts. The implementation of pesticide regulations has effectively stopped most research into novel antimicrobial compounds due to the cost of development and registration [3] It remains more financially viable for companies to develop formulations containing currently approved active compounds than to risk the cost of developing and attempting to gain authorization for novel antimicrobials. Many of the most widely available antimicrobial disinfectant and sanitizer products consist of combinations of a limited number of individual compounds. The central axiom that synergistic interactions can occur between antimicrobials with different mechanisms of action and target sites has resulted in the liberal use of claims of synergy when multicomponent disinfectants products are described and marketed
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