Use of a new, simple, laboratory method for screening the antimicrobial and antiviral properties of hand sanitizers

Purpose: To develop a simple, laboratory method for screening the antimicrobial/antiviral activity of hand sanitizers, to replace the more time consuming use of human volunteers. Methods: A Rapid Agar Plate Assay (RAPA) was developed that uses sterile agar plates to simulate skin surfaces. After treating the agar plates with putative hand sanitizers, the plates were inoculated with gram-positive S. aureus or gram-negative E. coli. Untreated agar plates served as controls. After incubation for 48 hours, the bacteria were recovered and stained with fluorescent dyes. The number of live/dead bacteria was quantitated by flow cytometry. For anti-viral activity, mammalian cell lines were grown to confluency and infected with noroviruses (murine norovirus or feline calicivirus), and the number of dead cells was quantitated as the logio of number of cells killed. A liquid hand soap without any antibacterial activity (LHS) was used as the control. A popular ethanol-based hand sanitizer (GHS) was compared to a new quaternary ammonium-containing bactericidal hand cream (ABC). Results: The liquid soap was not effective against either gram-positive or gram-negative bacteria, or viruses. Both GHS and ABC were very effective against S. aureus, but much less so against E. coli. Both GHS and ABC were even more effective against the two noroviruses that cause gastrointestinal diseases, than they were against gram-positive bacteria. These results support the use of RAPA as an effective laboratory screening test to evaluate the antibacterial/ antiviral activity of hand sanitizers or other antimicrobial products. This laboratory study showed that some no-rinse anti-bacterial hand sanitizers can inactivate viruses better than they can kill bacteria. Hand sanitizers can contribute to universal precautions used in dental offices.