An in situ antimicrobial susceptibility testing method based on in vivo measurements of chlorophyll α fluorescence

• A new rapid, easy, and accurate method for the evaluation of antibacterial properties
• Instrumental, based on a low cost chlorophyll a fluorescence spectrophotometer
• Can be applied in situ under any experimental conditions with no growth medium
• Higher resolution than existing quantitative standard methods

Up to now antimicrobial susceptibility testing (AST) methods are indirect and generally involve the manual counting of bacterial colonies following the extraction of microorganisms from the surface under study and their inoculation in a separate procedure. In this work, an in situ, direct and instrumental method for the evaluation and assessment of antibacterial properties of materials and surfaces is proposed. Instead of indirectly determining antibacterial activity using the typical gram(−) test organisms with the subsequent manual colony count or inhibition zone measurement, the proposed procedure, employs photosynthetic gram(−) cyanobacteria deposited directly onto the surface under study and assesses cell proliferation and viability by a quick, accurate and reproducible instrumental chlorophyll fluorescence spectrophotometric technique. In contrast with existing methods of determination of antibacterial properties, it produces high resolution and quantitative results and is so versatile that it could be used to evaluate the antibacterial properties of any compound (organic, inorganic, natural or man-made) under any experimental conditions, depending on the targeted application.