As a component of aseptic technique, Bunsen burners do not universally decrease deposition of microbe-containing...

Microbiologists often use Bunsen burners to reduce airborne microbial contamination in their workspace. In theory, the burner's flame pushes air-and the microbe-containing particles therein-up and away from research materials. This is purported to create a disinfected zone that improves asepsis. While such use of a Bunsen burner is promoted in numerous textbooks, peer-reviewed publications, and university-affiliated websites, our search for data on Bunsen burner efficacy revealed a dearth of experimental evidence in scientific literature. Therefore, we designed and conducted a series of laboratory experiments to test the utility of this method, hypothesizing that the flame would reduce airborne contamination. We intentionally inoculated the air in a laboratory space with bacteria, then collected data on the deposition of airborne contaminants using a paired settle plate method. On average, plates adjacent to an active Bunsen burner do not experience a reduction in colony-forming units (CFU) settling. Linear regression indicates that results are environmentally context dependent: plates adjacent to Bunsen burners with 18 mm flame diameter exhibit mildly decreased deposition of dry particles when control contamination rates exceed 83 CFU/min, but increased dry particle deposition at contamination rates below that cutoff. Duration of flame activity is not associated with improved aseptic outcomes, regardless of flame size or particle moisture. Taken together, these data suggest that 18 mm Bunsen burners should be selectively implemented only in situations of "high and dry" airborne contamination. Outside this specific context, their activity is either neutral or detrimental to laboratory asepsis.

The ability to manipulate and control microbial presence in built environments is imperative to research and medicine. The lack of documented evidence relating Bunsen burner use and airborne contamination led us to conclude that this element of aseptic technique has until now been supported primarily by lore and tradition rather than experimental data. Given that laboratory open flame use has financial, temporal, and safety implications for research institutions across the globe, we sought to determine whether it is a worthwhile investment of resources. Ultimately, our data suggest that this practice is not evidence-based and that, except in a specific subset of circumstances, Bunsen burners can be removed from classroom and laboratory practice without compromising research integrity.