Effect of Sodium Citrate on Growth of Bacteria in Blood Culture

Background: This study compared the growth of Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Streptococcus pneumoniae, and Haemophilus influenzae in blood culture bottles containing anticoagulants, sodium polyanethol sulfonate (SPS) and sodium citrate. Methods: One hundred and fifty colony forming units of five different bacterial species were inoculated into standard aerobic (SA) and standard anaerobic (SN) bottles and were combined with 5 mL of human blood in solution with SPS or sodium citrate. Time to detection (TTD) was then monitored using the BacT/ Alert 3D system (bioMerieux Inc.). Results: Compared to the bacteria-only controls, cultures containing S. aureus, E. coli, P. aeruginosa, and S. pneumoniae plus SPS blood or citrated blood trended toward reduced TTD in both SA and SN bottles; however, there was no significant difference in TTD between SPS and sodium citrate anticoagulant. Although H. influenzae showed a remarkable difference in TTD between SPS (SA 14.8 h, SN 15.0 h) and sodium citrate (SA 23.5 h, SN 18.3 h), this difference was not statistically significant (P=0.10). Conclusion: Addition of blood enhanced growth of bacteria. All experimental bacteria except H. influenzae showed similar TTD in SPS blood and citrated blood. These results support the usefulness of sodium citrate anticoagulant for artificial inoculation in blood culture bottles. (Ann Clin Microbiol 2013;16: 168-173)