Abstract
The aim of the present work was to evaluate several methods for analyzing the viability of bacteria after antibacterial photocatalytic treatment. Colony-forming unit (CFU) counting, metabolic activity assays based on resazurin and phenol red and the Live/Dead® BacLight™ bacterial viability assay (Live/Dead staining) were employed to assess photocatalytically treated Staphylococcus epidermidis and Streptococcus mutans. The results showed conformity between CFU counting and the metabolic activity assays, while Live/Dead staining showed a significantly higher viability post-treatment. This indicates that the Live/Dead staining test may not be suitable for assessing bacterial viability after photocatalytic treatment and that, in general, care should be taken when selecting a method for determining the viability of bacteria subjected to photocatalysis. The present findings are expected to become valuable for the development and evaluation of photocatalytically based disinfection applications.
Highlights
Photocatalysis of titanium dioxide (TiO2) has been widely investigated and successfully applied in a wide variety ofThere is a growing interest in applying TiO2 photocatalysis to disinfection and antibacterial applications (Allahverdiyev et al 2011; Robertson et al 2012; Sanchez et al 2012; Welch et al 2010; Lilja et al 2012)
We evaluated and compared several methods for analyzing bacteria treated with TiO2 photocatalysis, including Colony-forming unit (CFU) counting, metabolic activity assays based on resazurin and phenol red and Live/Dead staining
For assessing S. mutans viability, three methods were employed: metabolic activity assay based on phenol red, metabolic activity assay based on resazurin and Live/Dead staining
Summary
Photocatalysis of titanium dioxide (TiO2) has been widely investigated and successfully applied in a wide variety ofThere is a growing interest in applying TiO2 photocatalysis to disinfection and antibacterial applications (Allahverdiyev et al 2011; Robertson et al 2012; Sanchez et al 2012; Welch et al 2010; Lilja et al 2012). A number of different indicators are used for this purpose, including resazurin (Sandberg et al 2009), fluorescein diacetate (FDA) (Diaper et al 1992), tetrazolium salt (XTT) (Belanger et al 2011) and pH indicators like phenol red (Pantanella et al 2008). These metabolic activity tests rely on the production of detectable signals resulting from a reaction between the indicator and the metabolite intermediate (e.g., NADPH) or product (e.g., lactic acid) (Peeters et al 2008). Different strains of the same bacterial species or the same bacteria strain in planktonic or biofilm form may have different growth rates (Welch et al 2012; Mah and O’Toole 2001; Donlan 2001)
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