Combined serum bactericidal and phagocytic activities of defibrinated human blood against Serratia marcescens. Use of phenylbutazone to selectively block phagocytic killing activity and of Group A (phage tail) bacteriocins to kill extraphagocytic bacteria.

Fresh, defibrinated human blood (65 vol%) from normal adults reduced cell inocula of Serratia marcescens, comprising 'delayed serum-sensitive', 'pseudo-serum-resistant', and 'non-serum-sensitive' human serum susceptibility categories, by up to approximately 3 log10 units, provided cell inocula did not significantly exceed 10(5) colony-forming units/ml at 0 time. Phenylbutazone (2 mg/ml) antagonized neither serum bactericidal activity nor the biological activity of group A (phage tail) bacteriocins bA+ 16 and bA+ 18. These bacteriocins were suitable for killing extraphagocytic S. marcescens cells, since they were not internalized by peripheral blood leukocytes. Phenylbutazone at 2 mg/ml failed to interfere with ingestion of S. marcescens by leukocytes; however, this drug inhibited intraphagocytic killing of ingested S. marcescens bacteria. Pilot experiments, utilizing this latter system, disclosed that rifampin effectively killed intraphagolysosomal bacteria.