Analytical techniques to study microbial biofilm on abiotic surfaces: pros and cons of the main techniques currently in use.

Biofilm is a bacterial lifestyle widespread in microbial world and represents a concern in health care. Despite the great life expectancy related to advanced health care, the increasing numbers of biofilm-mediated infections remain a significant public health challenge. Moreover, the problem of biofilm-mediated infections becomes much more severe when biofilm colonizes medical devices and biomaterials. The public health risk due to microbial biofilm-related infections is a concern that requires full attention. However, the complexity of biofilm makes difficult its exhaustive analysis. Although biofilm represents a major challenge in both microbiological and hygiene areas, at now methods aimed to analyse biofilm formation and development are not standardized yet. Different methods have been employed to qualitatively and quantitatively evaluate biofilm each of which is useful to estimate a peculiar aspect of biofilm lifestyle. In the present review, fifteen assays for the qualitative and quantitative evaluation of bacterial biofilm colonizing abiotic substrates, such as medical devices, prosthesis or surfaces for food production together with advantages and limitations of each method were described and compared. Some methods are suited to quantify biofilm matrix while others are capable to evaluate both living and dead cells or quantify exclusively viable cells in biofilm. In particular, colorimetric methods to evaluate biofilm matrix (crystal violet; 1,9-dimethyl methylen blue and fluorescein-di-acetate methods) or viable cells (LIVE/DEAD BacLight, BioTimer Assay, resazurin, tetrazolium hydroxide salt methods) and genetic methods to estimate the bacterial population (PCR and FISH) are reported. Moreover, a section is dedicated to examine the performances of advanced microscopic techniques employed to study microbial biofilms (mass spectrometry; confocal laser scanning microscopy; Raman spectroscopy and electron microscopy). Because of its complexity, an exhaustive study of biofilm requires a combination of different experimental approaches as biochemical, genetic or physical ones.