If I am not mistaking, the XTT reduction technique uses cell viability (activity) as a component in the reaction resulting in the colored aspect that can be quantified. When it comes to the crystal violet assays, it's essentially and simply a dye of the biofilm. It gives a quantifiable and colored result also, which the intensity will vary depending on the quantity of biofilm present in a correlated way. This is also true in the XTT assay, but in this case, the ''age'' of the biofilm will matter. Hence, if you quantify a mature biofilm with the XTT, it might give you a lower detection because less active and viable cells will be measured.

I think the crystal violet will give different results because it stains also the matrix of the biofilm. Pseudomonas aeruginosa biofilm usually has a rich matrix.

I've used crystal violet (CV) and fluorescein di-acetate (FDA, - similar to that of XTT in that it looks at cellular activity) to study biofilms of P. aeruginosa. CV stains ALL biomass that is present, meaning non-viable materials (dead cells and EPS) are also stained. The FDA assay was slightly better in that it shows the activity of viable cells, however we know that sub populations of bacteria within a biofilm have a very slow growth rate which can affect this type of assay. Couple that with activity below the detection threshold and it might appear you have killed a biofilm when intact there are persister populations. The best way is to always enumerate the cells within a biofilm. Hope that helps! In all instances listed above, I was looking at the effects of an antimicrobial on biofilms.

CV and XTT methods are used to quantify biofilms. However, CV quantifies all biomass (live, dead and also de matrix of biofilm), while XTT only quantifies the metabolically active cells (live). So the results are quite different...

CV is a very simple and easy method and it stains all biomass and matrix in biofilm. But this method sometimes can have big variations due to the different staining/washing process. XTT and also TTC are respiratory indicators, so they measures metabolic active bacteria. For some bacteria, XTT / TTC gives more consistent results.

The paper below found that TTC were more specific to biofilm bacteria.

http://onlinelibrary.wiley.com/doi/10.1111/jam.12316/abstract;jsessionid=EEFCE32FF7A507890A9F4C30F1BEDA97.f03t04

Can someone give me the recipe for crystal violet stain used for biofilm detection?

@Josipa Check this article :Evaluation of different detection methods

of biofilm formation in the clinical isolates

Alexandre Fugère Salut Alexandre. Je suis Pierre à Pays-Bas. Je travailles de tester le formation de bioflm par TCP test. Alors, J'aimerais connaître combien violet crystal on va ajouter en le biofilm (0,1% ou 0,2%)? Merci beaucoup.

Pierre M.Q. Trinh De mon expérience, 0.1% était nettement suffisant! Les lavages sont importants!

Alexandre Fugère Je comprends maintenant. Donc, est-ce que tu peux me partager les documentaires pour ce info vueille? Parce que je besoins les références pour mon projet. Merci.