Correlating biological methods to assess Escherichia coli bacteria viability in silica gels

摘要

The viability of Escherichia coli bacteria entrapped in silica gels can be monitored using the Alamar Blue assay and ATP-metry, two complementary methods that correlate with the traditional plate count technique while avoiding its current limitations related to cell growth conditions. Assessment of bacterial cell viability is routinely performed using the plate count technique. This technique relies on the spreading of a cell suspension on solid nutrient media that is kept under usual optimal growth conditions, i.e. at 37 °C over 24 h for common bacteria. After this delay, each initial living cell has grown into a colony so that viability is given by the number of colony forming units (CFU) per mL of the starting suspension. However, there are two main situations where the plate count technique cannot be applied. The first one concerns cells whose growth conditions are uncommon, if not unknown. The second possibility is that cells have entered the so-called viable but non-culturable (VBNC) state where they are alive but have a very low metabolic activity and thus cannot be grown under usual conditions.