Growth Patterns of a Wide Spectrum of Organisms Encountered in Clinical Blood Cultures Using Both Hypertonic and Isotonic Media

Abstract

In an effort to determine how long a wide spectrum of organisms will survive in either an isotonic or a hypertonic blood culture system, all clinical blood culture flasks were subcultured on a daily basis for the first seven days of incubation and again on the fourteenth day. This subculture included all those flasks found to harbor organisms on previous subculture. Organisms such as members of the Enterobacteriaeceae and Pseudomonadaceae, as well as Staphylococcus aureus, Bacteroides spp., Eubacterium and Candida spp., survive for at least 14 days in both isotonic and hypertonic blood culture systems. However, organisms such as the various streptococci, H. influenzae, and N. meningitidis start to die off in hypertonic media within four days and in isotonic media within five days. Of 47 isolates of S. pneumoniae, 9 of N. meningitidis and 14 of H. influenzae obtained from the hypertonic system, only 21, 3 and 2 isolates, respectively, were still recoverable on the seventh day of incubation. In this study, parallel culture methods were used to compare the two systems, with the result that the hypertonic system allowed for recovery in 356 instances while the isotonic system allowed recovery in only 319 instances. It would appear from the results of this study that many organisms tend to die off more rapidly in a hypertonic system than in an isotonic system; however, fewer recoveries occur with the isotonic system.