The Relationship Between Platelets and Bacteria

In an attempt to clarify conflicting reports as to whether blood platelets are bactericidal, platelets were artificially contaminated with seven different bacteria: Bacillus subtilis, Escherichia coli, Enterobacter cloacae, Pseudomonas aeruginosa, Staphylococcus epidermidis, Streptococcus faecaiis, and Sarcina lutea. Employing many variations in the circumstances of the exposure, platelets were bactericidal for only Bacillus and possibly Sarcina. When platelet concentrates were contaminated with bacteria and left at room temperature for 48 hr, all organisms but one (Sarcina) grew out of control. However, this organism was also killed in cell-free plasma. The presence of platelets in plasma was found to enhance the growth of some organisms. These experiments indicate that platelets not only have a very limited bactericidal capability, but can protect certain bacteria from death due to other blood components.