Abstract
Other than the needs for infection control to investigate the survival and inactivation of airborne bacterial pathogens, there has been a growing interest in exploring bacterial communities in the air and the effect of environmental variables on them. However, the innate biological mechanism influencing the bacterial viability is still unclear. In this study, a mutant-based approach, using Escherichia coli as a model, was used to prove the concept that common stress-response genes are important for airborne survival of bacteria. Mutants with a single gene knockout that are known to respond to general stress (rpoS) and oxidative stress (oxyR, soxR) were selected in the study. Low relative humidity (RH), 30–40% was more detrimental to the bacteria than high RH, >90%. The log reduction of ∆rpoS was always higher than that of the parental strain at all RH levels but the ∆oxyR had a higher log reduction than the parental strain at intermediate RH only. ∆soxR had the same viability compared to the parental strain at all RH levels. The results hint that although different types and levels of stress are produced under different RH conditions, stress-response genes always play a role in the bacterial viability. This study is the first reporting the association between stress-response genes and viability of airborne bacteria.
Highlights
Other than the needs for infection control to investigate the survival and inactivation of airborne bacterial pathogens, there has been a growing interest in exploring bacterial communities in the air and the effect of environmental variables on them (Franzetti et al 2011; Tang 2009; Mohr 2007; Sun and Ariya 2006)
A high relative humidity (RH) condition (Fig. 1) preserved the bacteria the most compared to the intermediate (Fig. 2) and low RH (Fig. 3), the log reduction in survival of the parental strain at high RH still reached to about 0.5 log (Fig. 1), which is equivalent to less than 32% of the bacteria that survive from the aerosolization process
General stress‐respond to general stress (rpoS) gene Most of the bioaerosol studies investigated the effect of RH on bacterial viability were conducted decades ago by measuring some morphological or physiological changes of the bacteria as the end points (Cox and Baldwin 1967; Hess 1965; Bateman et al 1961; Dunklin and Puck 1948)
Summary
Other than the needs for infection control to investigate the survival and inactivation of airborne bacterial pathogens, there has been a growing interest in exploring bacterial communities in the air and the effect of environmental variables on them (Franzetti et al 2011; Tang 2009; Mohr 2007; Sun and Ariya 2006). Various bioaerosol studies have been conducted to determine the survival rate of airborne bacteria under different conditions to explain the bacterial diversity, predict the risk of airborne disease transmission and identify appropriate infectioncontrol strategies (Parienta et al 2011; Thompson et al 2011; Cox 1986). Understanding the stress response mechanism could provide a new biotechnology and engineering target to predict and control infection risks and facilitate the application of bioaerosol techniques to other fields [e.g. cloud condensation and climate change (Sun and Ariya 2006)]. We hypothesize that stress-response genes play a role to help the survival of airborne bacteria as in other environmental media
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