Pulmonary secretions accelerate the metabolic rate of Escherichia coli

A number of studies have suggested that bronchoalveolar lavage fluid (BALF) contributes to intrapulmonary antibacterial host defense, however the mechanisms underlying this interaction have not been defined. To better understand the effect of BALF on bacteria, we measured the metabolism of bacteria in the presence of human or rabbit BALF. Escherichia coli oxygen consumption significantly increases with exposure to BALF (2.9 +/- 0.2 (SEM) nmol/min) compared to incubation in a saline-glucose solution alone (1.8 +/- 0.1); the rate of 1-[14C]-glucose utilization is comparably increased. The effect on oxygen metabolism is dose dependent. The surfactant phospholipids produce a small stimulation of oxygen metabolism, but the major effect is caused by phospholipid-poor material less than 10,000 daltons in size. The activity is heat stable, pH stable, and resistant to the effects of proteases. These studies demonstrate that factor(s) within BALF increase the metabolic rate of bacteria. Further work is required to determine if this bacterial respiratory burst is a pathogenic mechanism or a reparative response to BALF induced injury.