In Vitro Correlation of Platelet Aggregation with Occurrence of Disseminated Intravascular Coagulation and Subacute Bacterial Endocarditis

Platelet-bacterial interactions were examined in vitro by incubating organisms isolated from patients with septicemia with normal platelet-rich plasma. The potency of various species of gram-positive and gram-negative bacteria to induce irreversible platelet aggregation was then determined in an aggregometer. The aggregation curves produced by the bacteria resembled the normal platelet response to collagen and were impeded by the presence of aspirin. Strains of Staphylococcus aureus and Pseudomonas aeruginosa isolated from 25 different patients produced maximum increases in light transmission and irreversible platelet aggregation with relatively rapid mean aggregation times; six of these patients had clinical and laboratory evidence of disseminated intravascular coagulation. In contrast, isolates of alpha streptococcus and Staphylococcus epidermidis induced irreversible platelet aggregation much less commonly and were associated with considerably longer mean aggregation times. None of the latter group of patients had evidence of disseminated intravascular coagulation. Isolates of bacteria from a small number of patients with subacute bacterial endocarditis uniformly induced irreversible platelet aggregation. Addition of paired bacterial isolates to normal platelet-rich plasma demonstrated a synergistic aggregation response. These data suggest that a relative hierarchy exists in bacterial strain potency to induce irreversible platelet aggregation. The rapidity and degree of aggregation in vitro correlated well with the clinical and laboratory evidence for subacute bacterial endocarditis and disseminated intravascular coagulation in vivo. These observations may provide useful adjunctive laboratory information to help establish the diagnosis of subacute bacterial endocarditis, especially in the clinical setting where the classical findings of endocarditis are not obvious during initial presentation.