Abstract: Disclosed are methods, systems, devices, and kits for diagnosing and/or monitoring a bacterial infection in a subject in need thereof. The methods, systems, devices, and kits are useful for identifying causative bacteria, such as Pseudomonas aeruginosa, by, for example, detecting the presence of one or more quorum sensing (QS) molecules associated with the bacteria. For P. aeruginosa these can include C4 homoserine lactone and/or C12 homoserine lactone. The methods, systems, devices, and kits can further include steps or features for obtaining diagnosis results and/or prescribing an antibiotic for the subject if, for example, the presence and/or increased levels of the QS molecule are detected. The methods, systems, devices, and kits can further include steps or features guiding a treatment regimen, such as whether to initiate or continue treatment of a bacterial infection caused by bacteria, such as P. aeruginosa, detected using the disclosed methods, systems, devices, and kits.