Biological specimens for microbiological analysis are often collected in BD Vacutainers®, which are not specifically designed for microbial recovery. Bacterial and fungal recovery was analyzed for glass and plastic tubes with or without clot-activating silica. No significant impact was found for the recovery of most bacteria and yeasts tested, however, Haemophilus influenzae recovery from cerebrospinal fluid was significantly reduced in both glass and plastic clot activator tubes.