Importance of stress-response genes to the survival of airborne Escherichia coli under different levels of relative humidity

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.Electronic supplementary materialThe online version of this article (doi:10.1186/s13568-017-0376-3) contains supplementary material, which is available to authorized users.

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“…Thus, the continuous expression of Catalase in our study implies that C. cladosporioides is always encountering an oxidative stress under dry periods. This meets the expectation that oxidative stress is an important stress under limited water availability conditions—particularly at 60% RH, because oxidative stress is relatively mild at higher RH (80%), and other types of stress are more detrimental than oxidative stress when the RH is further reduced below 60% …”

“…This meets the expectation that oxidative stress is an important stress under limited water availability conditions-particularly at 60% RH, because oxidative stress is relatively mild at higher RH (80%), and other types of stress are more detrimental than oxidative stress when the RH is further reduced below 60%. 27,28…”

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“…To determine the bacterial survival, both culturable and DNA counts of the collected bacteria were measured. The plate-count method and the DNA counts by quantitative polymerase chain reaction (qPCR) were used for determination of the culturability of the bacterial cells [30]. In brief, bacterial DNA was extracted using a QIAamp DNA Mini Kit (Qiagen, Hilden, Germany) following the manufacturer’s protocol.…”

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