Thermal resistance of naturally occurring airborne bacterial spores

Abstract

Simulation of a heat process used in the terminal dry-heat decontamination of the Viking spacecraft is reported. Naturally occurring airborne bacterial spores were collected on Teflon ribbons in selected spacecraft assembly areas and subsequently subjected to dry heat. Thermal inactivation experiments were conducted at 105, 111.7, 120, 125, 130, and 135 degrees C with a moisture level of 1.2 mg of water per liter. Heat survivors were recovered at temperatures of 135 degrees C when a 30-h heating cycle was employed. Survivors were recovered from all cycles studied and randomly selected for identification. The naturally occurring spore population was reduced an average of 2.2 to 4.4 log cycles from 105 to 135 degrees C. Heating cycles of 5 and 15 h at temperature were compared with the standard 30-h cycle at 111.7, 120, and 125 degrees C. No significant differences in inactivation (alpha = 0.05) were observed between 111.7 and 120 degrees C. The 30-h cycle differs from the 5-and 15-h cycles at 125 degrees C. Thus, the heating cycle can be reduced if a small fraction (about 10-3 to 10-4) of very resistant spores can be tolerated.

Recurrent Isolation of Extremotolerant Bacteria from the Clean Room Where Phoenix Spacecraft Components Were Assembled

“…While it has been observed that bacteria sometimes enter the clean room with humans (Puleo et al, 1978;Castro et al, 2004), other bacteria may be well adapted to the oligotrophic conditions of these environments as well as the chemicals used for cleaning the facility (La Duc et al, 2004). Furthermore, differences observed in microbial diversity and abundance between the three sampling dates suggest that these populations are not stable and may fluctuate significantly throughout the spacecraft assembly process.…”

“…These controlled conditions, coupled with periodic cleaning with chemical detergents (NASA-KSC, 1999), result in a harsh, nutrient-limited environment that is not conducive to microbial growth (La Duc et al, 2007a). However, although the stringent conditions within these facilities are effective in reducing the overall microbial load (Venkateswaran et al, 2001;La Duc et al, 2007a), they may also select for ''hardy'' microorganisms capable of tolerating prolonged periods of desiccation, extremes of temperature, and exposure to UV light or hydrogen peroxide (Puleo et al, 1978;La Duc et al, 2003, 2007aKempf et al, 2005;Newcombe et al, 2005;). A number of microbes have been isolated that can tolerate multiple environmental stresses and have been reported to survive under simulated and actual space conditions (Newcombe et al, 2005;Osman et al, 2008a).…”

Molecular bacterial community analysis of clean rooms where spacecraft are assembled

“…Many oligotrophic microorganisms are capable of colonizing inorganic surfaces like metal (Nagarkar et al , 2001) or glass and the presence of such microorganisms may lead to many problems for space missions, including biocontamination, biofouling, and biodeterioration (Wainwright et al , 1993). Strains isolated from these environments have also been shown to tolerate decontamination strategies, such as UV and gamma radiation treatment (Puleo et al , 1978; La Duc et al , 2003, 2007; Newcombe et al , 2005).…”

Draft Genome Sequences of 12 Dry-Heat-Resistant Bacillus Strains Isolated from the Cleanrooms Where the Viking Spacecraft Were Assembled

“…The Viking 1 and 2 spacecraft were launched in August and September 1975, respectively, to explore the planet Mars and specifically look for signs of extant extraterrestrial life ( 1 ). As part of a routine environmental microbial monitoring of the Vehicle Assembly Building (VAB) and the Manned Spacecraft Operations Building (MSOB) facilities in Cape Canaveral, FL, 32 Teflon ribbons were left out for 7 days and used to collect airborne microorganisms ( 2 ). The Teflon ribbons were then exposed to a total of 6 different heat treatments at three different time cycles ( 2 ).…”