Viable bacteria may be detected in biological samples by exposing bacterial cultures obtained from the samples to transducing particles having a known host range. Such transducing particles carry a heterologous gene capable of altering the phenotype of the bacteria in a readily detectable manner. For example, the transducing particles may carry an ice nucleation gene and the alteration of phenotype may be detected using an ice nucleation assay. By employing a panel of phage, unknown bacteria may be typed based on the pattern of reactivity observed. The method is particularly useful for detecting viable bacteria which may have been debilitated by exposure to sterilizing conditions, such as in food processing. The method is also useful for tracking a target bacteria in the ambient environment.