Hypothesis: Previous studies on alterations in phagocytosis and bacterial killing after trauma have yielded conflicting results. We hypothesize that these changes are variable, depending on the species of bacteria used to assay these variables.
Design: Blood samples from patients were assayed by means of flow cytometry for phagocytosis and reactive oxygen intermediate generation. Several common clinical pathogens were used: Escherichia coli, Klebsiella pneumoniae, and 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. pneumoniae. 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 were taking corticosteroids before hospital admission or who were administered corticosteroids before blood was drawn were not studied. Isolated head injuries or limb fractures were also excluded. Controls consisted of healthy volunteers.
Main outcome measures: The ingestion of bacteria by neutrophils and the generation of reactive oxygen intermediates.
Results: After trauma, phagocytosis of E. coli was enhanced, whereas ingestion of K. pneumoniae was depressed. Ingestion of S aureus remained unchanged. The generation of reactive oxygen intermediates was depressed after incubation with E. coli and unchanged with K. pneumoniae, but enhanced with S. aureus.
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 early infections after trauma.