Abstract: The invention relates to a compound of formula Ia and/or formula Ib: or a pharmaceutically acceptable salt, solvate or prodrug thereof, where the groups are defined herein. The invention also relates to a pharmaceutical formulation comprising the compound for treating or detecting a microbial infection in a subject, a method of determining antimicrobial resistance of a microbial infection using the compound, and a method of determining an effective dose of one or more antimicrobial agents to kill a microorganism using the compound.