Microbial Aerosols Generated from Standard Microbiological Laboratory Procedures

Abstract

Background: Modern microbiology laboratories are designed to protect workers and the environment from microbial aerosols produced during microbiological procedures and accidents. However, there is only limited data available on the aerosols generated from common microbiology procedures.

Methods: A series of common microbiological procedures were undertaken with high concentration spore suspensions while air samplers were operated to sample the aerosols generated. Surface contamination from droplets was visualized using sodium fluorescein within the suspension. A total of 36 procedures were studied using different sample volumes (0.1-10 mL) and two spore suspension titers (10⁷ and 10⁹ colony forming units [cfu]/mL).

Results: The aerosol concentrations generated varied from 0 to 13,000 cfu/m³. There was evidence to suggest that titer, volume, and poor use of equipment were significant factors in increased aerosol generation from some of the procedures. A risk assessment undertaken using the data showed that any aerosol generated from these processes would be contained within a correctly operating biological safety cabinet. Therefore, with these procedures, the operator and the environment would not require any additional protective measures such as respiratory protective equipment or a negative pressure laboratory to prevent aerosol exposure or release.

Conclusions: Aerosol generation from common laboratory processes can be minimized by reducing sample volumes and concentrations if possible. Training laboratory staff in good microbiological techniques would further mitigate aerosols generated from common laboratory processes.

Keywords: aerosol generation; bacterial spore; laboratory procedures; pipetting; spillage.

Figure 1.

Mean aerosol concentrations generated from the experiments using a 10⁹ cfu/mL spore suspension. All tests were performed in triplicate, except serial dilution 1 mL (n = 4) and 10 mL (n = 4), vortex mixing universal 1 mL (n = 4) and 10 mL (n = 4), handshake universal 1 mL (n = 4) and 10 mL (n = 4), and plating with blue loop and spreader (n = 5). Error bars are standard deviations of the means.

Figure 2.

Mean aerosol concentrations generated from the experiments using the 10⁷ cfu/mL spore suspension. N = 3 for all tests, and error bars are standard deviations of the means.

Figure 3.

Mean aerosol concentrations generated from the experiments undertaken with poor practice, accidents, and specialist equipment using 10⁷ (black bar) and 10⁹ (gray bars) cfu/mL spore suspensions. N = 3 and error bars are standard deviations of the means.

Figure 4.

Mean number of splashes counted on the Benchkote immediately under the area where the procedure was completed. ** Indicates that there was a large spillage rather than countable splashes. All tests were completed using the 10⁹ cfu/mL bacterial spore suspension. Error bars are standard deviations of the means.