Aerosol Survival of Escherichia coli B Disseminated from the Dry State

Abstract

Survival was determined for Escherichia coli B disseminated as an aerosol from the dry state. Survival in nitrogen, like that for wet dissemination, was better at low than at high relative humidity (RH). At high RH, survival was characterized by critical zones of instability in survival as a function of RH, instability occurring at 100, 95, 78, 70, and 60% RH. In air, survival was inferior to that in nitrogen at low RH, whereas the converse was found at high RH. The effect was attributed to oxygen. In general, results support the conclusion that to the first approximation survival is related to bacterial water content, the latter increasing with RH. However, a more detailed analysis of results indicates that survival might not be exactly related to bacterial water content. It is shown that death occurred because of rehydration and that the pretreatment of E. coli B affected its aerosol stability characteristics; i.e., wet and dry disseminated aerosols are not equivalent.

Aerosol Survival of Pasteurella tularensis Disseminated from the Wet and Dry States

“…Also, measurements of equilibration times of droplets (3) tend to exclude lack of equilibration as being the cause. These conclusions, as those for E. coli B (11), indicate that aerosol survival is not directly related to bacterial water activity or water content. An alternative at this stage cannot be suggested, although it is considered possible that the process of freeze-drying used to prepare the dry powders had an effect in addition to removing water and causing part of the population to lose viability (40%).…”

“…2 and 4), i.e., a shift of the order of 20% RH. A smaller shift in the opposite direction was found for E. coli B when wet-and dry-disseminated (11). Exact numerical equivalence of the position of minimum survival for wet and dry dissemination would not be expected because of hysteresis in sorption isotherms.…”

“…Most of these details have been published by Cox (4,7,11,13); additional detail is given below. The growth medium for P. tularensis live vaccine strain (LVS) was, per 100 ml of distilled water, 2 g of NZ amine A (Sheffield Chemical Co.), 0.5 g of Basamin Busch yeast product, 0.5 g of NaCl, 1 ml of stock thiamine solution (0.01%), and 1 ml of stock KxHyPO4 solution (22.5% K2HP04, 5.3% KH2PO4).…”

“…A review by Anderson and Cox (1) showed that strict comparisons of survival of bacteria in aerosols generated from the wet and dry states could not be found in the literature. Recently, Cox (11) made such a comparison for Escherichia coli B and showed that aerosol survival might not be exactly related to bacterial water content. Also, it was shown that death occurred because of rehydration as previously suggested (3-8, 10, 11), that oxygen influenced aerosol survival as indicated previously (2,4,8,11,12,16,17), and that aerosols disseminated from the wet and dry states were not equivalent.…”

“…Recently, Cox (11) made such a comparison for Escherichia coli B and showed that aerosol survival might not be exactly related to bacterial water content. Also, it was shown that death occurred because of rehydration as previously suggested (3-8, 10, 11), that oxygen influenced aerosol survival as indicated previously (2,4,8,11,12,16,17), and that aerosols disseminated from the wet and dry states were not equivalent. The present paper describes results obtained with Pasteurella tularensis disseminated from the wet and dry states (from hereon referred to as wet and dry dissemination), since it was of great interest to determine if the results obtained with E. coli B appertained to another gram-negative bacterium.…”