Rapid identification of Staphylococcus aureus and Streptococcus pneumoniae from blood cultures.

Simultaneous application of the lysostaphin sensitivity test for identification of Staphylococcus aureus and the deoxycholate test for the identification of Streptococcus pneumoniae was evaluated for reliability in rapid identification (1 h) of these organisms from blood cultures by using BACTEC 6B and 7C bottles. The procedure was applied to 127 cultures, 74 lysostaphin tests and 53 deoxycholate tests. Lysostaphin-tested organisms included 23 S. aureus, 40 Staphylococcus epidermidis, 1 Listeria sp., 1 Peptococcus sp., 2 Micrococcus sp., 2 diphtheroids, and 5 mixed cultures. Deoxycholate-tested organisms included 14 S. pneumoniae, 32 Streptococcus spp. (not S. pneumoniae), 1 Listeria sp., 1 Peptococcus sp., 2 diphtheroids, and 3 mixed cultures. Analysis of the data revealed positive and negative predictive values of 95.8 and 94%, respectively, for the lysostaphin test and 100 and 97.4%, respectively, for the deoxycholate test. The combined tests provide rapid reliable identification or elimination of S. aureus and S. pneumoniae in blood cultures.