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 a cationic anti-microbial peptide that is degradable by an enzyme produced and/or secreted by a microorganism, and detecting degradation or the absence of degradation of the peptide, as an indicator of the presence or absence of the enzyme in the sample, and thus indicative of the presence or absence of a microorganism in the sample. The present invention also features a biosensor for detecting the presence or absence of a microorganism in a sample.