Enzyme-linked immunosorbent assay for quantitation of attachment and ingestion stages of bacterial phagocytosis

Research on phagocytosis of bacteria is often hampered by the inability to distinguish quantitatively between bacteria that have been ingested by phagocytic cells and those which are attached to the surface of the cells. A method using the enzyme-linked immunosorbent assay technique to simply and accurately measure the rate of bacterial ingestion by phagocytic cells is described. The method is based on the ability of antibacterial antibodies to bind to bacteria attached to but not internalized by phagocytic cells. The attached bacteria were quantitated by enzyme-linked immunosorbent assay. Compared with the number of bacteria at zero time (17 bacteria attached per phagocyte) only 10 to 20% of the bacteria remained attached to phagocytic cells after incubation for 30 min at 37°C. The decrease in detected attached bacteria at 37°C was due to internalization of the bacteria by phagocytic cells, since upon disruption of the monolayer, most of the ingested bacteria were recovered, and at 4°C, most of the bacteria remained extracellularly attached. The proposed attachment and ingestion assay is easy to perform, allows the detection of specific atachment of test bacteria, and provides objective quantitation of attached and ingested bacteria. Most importantly, the assay allows testing of ingestion rates of bacteria under many variables on the same day.