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Planetary and sample return missions require surface cleaning procedures using biocides. However, a deep understanding of how microorganisms respond to biocides is needed. The response of different Salmonella serovars to defined concentrations of chlorine, chlorine dioxide, and cetylpyridinium chloride (CPC) was studied. Microbial responses in terms of culturability, and virulence gene expression were also evaluated. Inactivation when exposed to chlorine and CPC was extremely rapid. Inactivation due to chlorine dioxide was, however, gradual. Exposure to these biocides caused a number of physiological states in Salmonella cells including dormancy, injury, and a viable but non-culturable state. Based on real-time PCR assays, all virulence-related genes were down-regulated in the presence of chlorine, chlorine dioxide and CPC. These studies highlight the importance of understanding the possible responses of organisms to biocides before they are used in mission critical applications such as pre-flight cleaning and laboratory protocols involved in sample return missions. [ABSTRACT FROM PUBLISHER]