期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2002
卷号：99
期号：12
页码：8289-8294
DOI：10.1073/pnas.122244799
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：We have examined the effect of neutrophil concentration on killing of a clinical isolate of Staphylococcus epidermidis. Human neutrophils at concentrations varying from 105 to 107 per ml were mixed in suspension with S. epidermidis at concentrations varying from 103 to 108 colony-forming units/ml, and the concentration of viable bacteria was assayed after various times at 37{degrees}C. The rate of bacterial killing depended on the concentration of neutrophils and not on the ratio of neutrophils to bacteria. Below a critical concentration of neutrophils, bacteria growth was greater than neutrophil killing of bacteria even when the ratio of neutrophils to bacteria was 100:1. We fitted the time course of bacterial concentration and its dependence on neutrophil concentration with an exponential function, the exponent of which is (-kp + g)t, where k is the second-order rate constant for bacterial killing, p is the neutrophil concentration, g is the first-order rate constant for bacterial growth, and t is time. We found that k {approx} 2 x 10-8 ml per neutrophil per min, and g {approx} 8 x 10-3/min. Only when p is greater than g/k, which we call the critical neutrophil concentration, does the bacterial concentration fall. Under optimal assay conditions, the critical neutrophil concentration was 3-4 x 105 per ml, a value very close to that ([≤]5 x 105 per ml) known to predispose humans to bacterial and fungal infections.
