Differences between bacterial species shown by simultaneous assessment of neutrophil phagocytosis and generation of reactive oxygen intermediates in trauma patients

Hypothesis: Previous studies on alterations in phagocytosis and bacterial k illing after trauma have yielded conflicting results. We hypothesize that t hese changes are variable, depending on the species of bacteria used to ass ay these variables. Design: Blood samples from patients were assayed by means of flow cytometry for phagocytosis and reactive oxygen intermediate generation. Several comm on clinical pathogens were used: Escherichia coli, Klebsiella pneumoniae, a nd Staphylococcus aureus. Results were compared with those from controls. Setting: Regional level I trauma center. Patients: Ten consecutive patients were studied with E coli and K pneumonia e. Five of these were also studied with S aureus. Patients were 18 years of age or older, with an Injury Severity Score of 16 or more. Patients who we re taking corticosteroids before hospital admission or who were administere d corticosteroids before blood was drawn were not studied. Isolated head in juries or limb fractures were also excluded. Controls consisted of healthy volunteers. Main Outcome Measures: The ingestion of bacteria by neutrophils and the gen eration of reactive oxygen intermediates. Results: After trauma, phagocytosis of E coli was enhanced, whereas ingesti on of K pneumoniae was depressed. Ingestion of S aureus remained unchanged. The generation of reactive oxygen intermediates was depressed after incuba tion with E coli and unchanged with K pneumoniae, but enhanced with S aureu s. Conclusions: Neutrophil response to trauma is dependent on which bacterial species the cell is attempting to kill. This may, in part, explain why only a limited number of bacterial species cause a significant proportion of ea rly infections after trauma.