Effects of Oxygen on Aerosolized Serratia marcescens

Abstract

Suspensions of Serratia marcescens (ATCC strain 14041) in water were aerosolized in a rotating drum in the presence of various concentrations of oxygen. The colony-forming ability of aerosolized organisms was rapidly destroyed by contact with 0.25% or more oxygen at 40% relative humidity (RH) and 25 C, but was almost unimpaired for at least 5 hr in nitrogen containing not more than 10 ppm of oxygen. Completely hydrated organisms were insensitive to oxygen at pressures up to 100 psi for 4 hr. No loss in viability occurred in aerosols of washed cells in air at 97% RH. It is proposed that dehydration of the aerosolized cell results in sensitization to lethal effects of oxygen, but is not the primary cause of death. Mn ++ , Co ++ , glycerol, and thiourea enhanced the biological stability of aerosols in air. Numerous similarities between the effects of oxygen in this system and in systems using freeze-dried or irradiated organisms or cell-free enzymes support the hypothesis that closely related mechanisms are involved.

Oxidative Stress Contributes to Bacterial Airborne Loss of Viability

“…Thus, the clearest impact of changing the gas phase from air to nitrogen is observed at the lowest RH, with the average viability after 20 min in 30% RH air being 9% ± 6% and the average viability in 30% RH nitrogen being 83% ± 27%. These results are in agreement with the findings of early rotating drum studies, in which a decreased airborne loss of viability was observed in the absence of oxygen for both E. coli and Serratia marcescens ( 17 – 19 , 56 ), as well as a more recent study of the effects of spray drying on Lactococcus lactis ( 57 ).…”

“…1C ). This RH influence is in qualitative agreement with previous studies of bacterial airborne viability that show a positive correlation between RH and the viability of the bacteria ( 19 , 37 – 39 ). Although, an opposite trend is occasionally reported in older studies ( 40 ).…”

“…Evidence of the harmful nature of the airborne microenvironment can be seen in many studies of bacterial airborne survival. Studies using rotating drums ( 17 – 19 ), the Tandem Aged Respiratory Droplet Investigation System (TARDIS) ( 20 ), and Controlled Electrodynamic Levitation and Extraction of Bioaerosols onto a Substrate (CELEBS) ( 21 , 22 ), have reported a time dependent loss of culturability in bacteria exposed to airborne conditions for a variety of different bacterial species under a variety of different conditions. However, the exact mechanisms driving this loss of viability remain uncertain.…”