Gram-Typing Using Conjugated Oligoelectrolytes

Abstract

It is shown that Gram-type differentiation, an essential tool in microbiology, can now be easily accomplished by using the chain-elongated conjugated oligoelectrolyte COE-S6. Specifically, COE-S6 can be used as a fluorescent membrane probe that distinguishes between Gram-negative and Gram-positive bacteria in a single step. Confocal microscopy of labeled microorganisms and differential scanning calorimetry with phospholipid- and lipopolysaccharide-containing model membranes suggest that lipopolysaccharides impede COE-S6 membrane intercalation in Gram-negative bacteria. Both Gram-types within a mixture are discretely labeled by counterstaining COE-S6 with the nonspecific and lipophilic membrane probe FM 4–64. This single-step procedure allows for the in situ visualization of individual Gram-types in complex polymicrobial biofilms. Given that COE-S6 fluorescence intensity increases considerably post intercalation, it can be used for the detection of Gram-positive bacteria by the naked eye. COE-S6 does not inhibit bacterial growth and is simple to use, making it a promising membrane-specific fluorescent probe.