THE NONRANDOM BINDING DISTRIBUTION OF STREPTOCOCCUS-PNEUMONIAE TO TYPE-II PNEUMOCYTES IN CULTURE IS DEPENDENT ON THE RELATIVE DISTRIBUTION OF CELLS AMONG THE PHASES OF THE CELL-CYCLE

The adherence of Streptococcus pneumoniae to epithelial (A549) lung ce lls was studied and the bacterial binding distribution was found to be nonrandom (non-Gaussian). Analysis of the dependency of bacterial bin ding on the cell cycle of A549 cells revealed that approximately 1.8 t imes more bacteria bind to G(2) cells than to G(0)-G(1) phase cells. F urthermore, bacterial binding curves exhibited a plateau of binding to G(2) cells at a normalized bacteria to cell ratio approximately 1.8 t imes larger than that at which the plateau of binding to G(0)G(1) cell was observed. Since G(2) cells are on average 1.4-1.5 times larger th an G(0)-G(1) cells, the results indicate that bacterial binding is pro portional to cell size and not to the preferential binding (higher aff inity) of bacteria to A549 cells in the G(2) phase. Finally, the non-G aussian distribution of bacterial binding could be mathematically mode led by a linear combination of three Gaussian distributions each repre senting bacterial binding to cells in a particular phase of the cell c ycle (G(0)-G(1), S, and G(2)M). Because the Gaussian function contains a term that takes into account the relative number of cells in each o f the phases, this last result implies that the overall (non-Gaussian) binding distribution (and hence the median of bacterial binding) can be highly sensitive to the relative proportion of cells in the various phases of the cell cycle.