ABSTRACT

The actual methods used by laboratories for antimicrobial susceptibility testing should be determined by an analysis of the fiscal and personnel resources available, the workload and patient population to be served, the type of results desired by clinicians, and the expertise of laboratory personnel. Routine susceptibility testing is, for most laboratories, limited to relatively nonfastidious bacteria which grow aerobically. The cells growing on artificial media may have higher growth rates and therefore increased antibiotic susceptibility compared to slower growing cells in nutrient- and/or iron-depleted tissues or biofilms that may be present at the site of infection. Pertinent clinical information about the patient should accompany the clinical specimen sent for culture to allow the microbiologist to determine if antibiotic susceptibility testing is indicated. Whichever susceptibility test system a laboratory uses, a critical determinant of the clinical relevance of the results is the size of the inoculum employed.