Susceptibility to antibacterials and compared metabolism of suspended bacteria versus embedded bacteria in biofilms

Abstract

Bacterial resistance in biofilms to antiseptics is a well-known phenomenon for which numerous explanations have been suggested. In a dynamic flow model using an E. coli biofilm, a phenolic disinfectant displayed bactericidal activity only at a concentration five times greater than that effective against suspended bacteria. It is now established that phenols are effective antibacterials only for protein-synthesizing bacteria. Hence the question arose as to whether deeply embedded bacteria in our biofilms still exhibited an active metabolism. Therefore we evaluated the respiratory activity and the intracellular ATP level in biofilm bacteria, before and after contact with the disinfectant. The β-galactosidase activity, induced by the addition of lactose to the medium on day 4 (the day before the test), was measured in order to check whether diffusion of exogenous molecules through the biofilm was easily achieved. The results suggested that deeper layers of bacteria in five-day-old E. coli biofilms displayed reduced metabolic activity compared to the bacteria in suspension. Nevertheless, removal of the upper bacterial layers with a disinfectant induced recovery of the previously dormant metabolism. © 1994.