Susceptibility Testing Guides Antibiotic Choice

Clinical laboratories test samples taken from patients suspected of having a microbial infection. The first task is to identify the pathogen. The traditional approach is to spread the isolate on the surface of an agar plate that is then incubated at body temperature for a day or so. Bacteria and fungi grow on the agar, giving rise to visible colonies whose size, shape, and color help identify the microbe species. Special ingredients in growth media also aid in species identification. More recently, nucleic acid hybridization methods using unique identifiers in rRNA provide rapid, accurate identification. A major problem confronting the clinical microbiologist is determining which colonies on an agar plate are pathogens and which are contam....