Degradation of non-opsonized 32P-labelled E. coli by unstimulated mouse peritoneal macrophages. Evaluation of a method.

Five hours after the ingestion of non-opsonized E. coli by mouse peritoneal macrophages in vitro, 60-70 per cent of the bacteria were killed, estimated as decrease in colony forming units. When employing 32P-labelled E. coli, 50-60 per cent of the radioactivity was released to the medium by the macrophages during the same period of time. The mean number of visually-counted bacteria per macrophage was constant in the post-ingestive period. The macrophages killed the bacteria without early destruction. The release of radioactivity seemed to reflect the degradation of bacteria in the macrophages.