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Digital archive of theses discussed at the University of Pisa


Thesis etd-02252010-152744

Thesis type
Tesi di dottorato di ricerca
Thesis title
Comparative transcriptome and phenotype analysis of Bacillus cereus in response to disinfectant treatments
Academic discipline
Course of study
tutor Prof.ssa Senesi, Sonia
  • Bacillus cereus
  • biofilm
  • disinfectant
  • transcriptome
Graduation session start date
Release date
Nowadays antimicrobial chemicals are widely applied in order to remove bacteria from the environment. However, the bacterial response to various disinfectants is still unclear. In the present study, the physiological and genome-wide transcriptional responses of Bacillus cereus ATCC 14579 planktonic and biofilm cells exposed to four different disinfectants (i.e., benzalkonium chloride, sodium hypochlorite, hydrogen peroxide, and peracetic acid) were analyzed. In order to gain a more comprehensive understanding of the response of these bacterial populations to disinfectant treatment, different concentrations of the antimicrobial compounds were used. The simultaneous analysis of the transcriptional responses of planktonic and sessile B. cereus cells upon exposure to the different disinfectants revealed significant differences between these bacterial populations. Notably, even though in both bacterial populations several genes related to energy metabolism were affected, distinct pathways were found to be down-regulated in biofilm or in planktonic cells after disinfectant treatment. Moreover, a generalized up-regulation of genes involved in the general and oxidative stress responses was observed only in planktonic cells. The comparative genome-wide analysis of planktonic cells treated with disinfectants revealed that the disinfectants we used induced specific responses. Exposure to benzalkonium chloride, a disinfectant known to induce membrane damage, specifically induced genes involved in fatty acid metabolism. Benzalkonium chloride induced-membrane damage was confirmed by fluorescence microscopy and fatty acid analysis confirmed that fatty acid composition of cell membrane was affected upon exposure to benzalkonium chloride. Sodium hypochlorite was shown to induce genes involved in sulfur and sulfur-containing amino acids metabolism, which correlated with the observed sodium hypochlorite-specific induction of oxidation of sulphydryl groups. Hydrogen peroxide and peracetic acid exposures induced genes involved in DNA damage and SOS response. Notably, hydrogen peroxide and peracetic acid-treated cells exhibited higher mutation rates corroborating with the induced SOS response.
Understanding the mechanisms displayed by microorganisms coping with disinfectants-induced stress may allow for design of more efficient sequential and/or disinfectant combination treatments.