The present invention relates to a method of detecting the presence of target microorganisms in a biological sample and of simultaneously determining the susceptibility of the microorganisms to antimicrobial agents. The target microbial organisms may be urinary pathogens. The methods include the steps of providing a multicompartment assay device with at least one compartment containing a medium capable of sustaining the growth of total viable microorganisms, at least one compartment containing a medium capable of sustaining the growth of target microorganisms, and at least one compartment containing an antimicrobial susceptibility interpretation medium. A biological sample is placed in each compartment and the presence and antimicrobial susceptibility of the target microorganisms which may be present is determined by analyzing which compartments exhibit microbial growth.