Should we care about transmission of infectious bacterial agents through serum handling?

Immunological assays are valuable diagnostic tools to detect infections due to most of bacterial microorganisms. However, the question is how much safe are the common serum samples used as sources of antibodies in these assays? Here, we experimentally followed the issue. 10-fold serial dilutions of two Gram-positive, Staphylococcus aureus and Bacillus cereus, and one Gram-negative bacteria, Escherichia coli, were prepared and spiked into freshly taken blood samples of human and four animal species including sheep, goat, cattle, and horse. After blood clotting, serum samples were examined by colony count method before and after a centrifugation step followed by an observation with a scanning electron microscope. No bacteria grew from both centrifuged and non-centrifuged serum samples contained at least 7.5 × 10², 7.5 × 10⁵, and 7.5 × 10⁵ CFU/ml of S. aureus, B. cereus, and E. coli, respectively. Moreover, routine centrifugation criteria did not show any significant effect on decrease of bacterial cells in sera. The results suggest that we can handle serum samples of apparently healthy humans and animal species without deep concern for possibility of transmission of infectious bacterial agents. However, this supposition should not completely be excluded.