Purpose: The purpose of this work was to explore the ability of Listeria innocua to contaminate a surface after the organisms become aerosolized. Environmental factors including relative humidity, distance from source, and surface wetness that may influence the ability of the organisms to survive and attach to surfaces were explored.
Methods: Listeria innocua was nebulized into a biosafety chamber (~5 log CFU in 1 ml), and the environment was manipulated and contained within this chamber with a combination of four durations and two humidity levels (83% and 65%). Oxford agar media, stainless steel coupons and polyethylene coupons were placed in the chamber at three distances from the nebulizer. An Airport MD8 Air Sampler was used to sample the air, and the recovery of Listeria after 7, 12, 22 and 42 minutes was determined.
Results: The three sample surfaces yielded a greater mean recovery of 2.7 cells/cm2 at 83% humidity compared to 0.45 cells/cm2 at 65% humidity. Recovery from air was significantly higher (2.2 mean cells/L) at 7 or 12 min after nebulization (83% humidity) compared to other time/humidity combinations (0.42 mean cells/L).
Significance: Understanding the survival rate of aerosolized Listeria and the time interval that these aerosolized bacteria can still colonize a food contact surface will enhance our efforts to prevent transmission. If Listeria monocytogenes behaves in same manner as Listeria innocua under similar conditions, correlations can be made. The food industry could apply proper precautions when either organism is detected.