Described herein are methods of detecting a wound infection and for detecting the presence or absence of microorganisms, for example, wound pathogens in a sample, by contacting a sample with an enzyme produced and/or secreted by the bacteria, and detecting modification or the absence of modification of the substrate, as an indicator of the presence or absence of the enzyme in the sample. The present invention also features a biosensor for detecting the presence or absence of bacteria in a sample.