Growth State of Aerosolized Bacillus Altitudinis Impacts its UV Susceptibility

EMILY KRAUS, Samuel Bryan, Margot Thomas Gatel, Adam Gillison, Amaya GarciaCostas, Sonia Kreidenweis, Mark Hernandez, University of Colorado Boulder

     Abstract Number: 503
     Working Group: Reducing Aerosol Exposure with Control Technologies and Interventions

Abstract
Airborne pathogens continue to pose significant public health risks in indoor congregate spaces. UV disinfection can effectively inactivate airborne pathogens in the built environment but inconsistent inactivation results in lab studies have limited broader deployment of UV technologies. This work examines how an oft overlooked biological factor of growth stage influences UV₂₅₄ susceptibility of a UV-tolerant airborne isolate closely related to Bacillus altitudinis.

Airborne UV susceptibility experiments were conducted in a 10m³ chamber under two relative humidity levels (25% and 60%) to simulate common indoor conditions. B. altitudinis was cultured to a defined growth stage (exponential or stationary) prior to aerosolization in the chamber with a Collison nebulizer. Five-minute composite samples (~40 L air) were collected via condensation capture (VIVAS) over the course of 50 mins. Susceptibility at exponential and stationary phase was assessed with counts of colony-forming units (CFUs/L air) and genome equivalents (ge/L air) with propidium monoazide quantitative PCR (PMA-qPCR) across four doses of UV₂₅₄ exposure to calculate inactivation rate constants (k values).

Preliminary results indicate that stationary phase B. altitudinis is distinctly less susceptible to UV₂₅₄ exposure compared to the same isolate in exponential phase. Furthermore, general airborne persistence of B. altitudinis (without exposure to UV) is heightened in stationary phase. Results may be indicative of the upregulation of DNA repair and stress response mechanisms that occur when bacteria progress into the stationary phase of their cell cycle.

Results from this work address a critical knowledge gap by characterizing a previously unaccounted biological variable affecting UV disinfection efficacy in laboratory studies. Collectively, these findings can inform on the standardization of UV disinfection challenges to support technology adoption and safer, more effective airborne pathogen control in occupied indoor spaces.