Surface thermodynamics of phagocytic ingestion of non-opsonized bacteria by granulocytes in liquids of different surface tensions.

The free energy of engulfment of four bacterial species by human granulocytes is calculated from contact angle data as a function of the surface tension gamma LV of the suspending liquid. The resulting curves predict that at low liquid surface tensions gamma LV, the phagocytic ingestion increases with decreasing hydrophobicity of the bacteria while at high surface tensions gamma LV, it increases with increasing hydrophobicity. Furthermore, these curves reach a minimum at values of gamma LV equal to the surface tension gamma LV of the bacteria. The experimental results support these predictions. Thus, the determination of the surface tension of the suspending medium at which phagocytic ingestion becomes minimum represents a novel technique to establish the surface tension of ingested particles, such as bacteria. The results obtained in this fashion for the four bacterial species are in good agreement with those obtained from contact angles, as well as those derived from bacterial adhesion experiments.