FIG. 1.

PCR inhibition occurring in the context of air samples. DNA was prepared from the filters and used as a template in the mitochondrial PCR as described in the text. Lane 1, 10³ P. carinii organisms spiked onto a filter previously exposed to a contaminated indoor environment; lane 2, 10² P. carinii organisms spiked onto a filter previously exposed to a contaminated indoor environment; lane 3, 10⁴ P. carinii organisms spiked onto a filter previously exposed to the outdoor environment; Lane 4, 10³ P. carinii organisms spiked onto a filter exposed to the outdoor environment; lane 5, 10² P. carinii organisms spiked onto a filter previously exposed to the outdoor environment. Lane 6, 10³ P. carinii organisms spiked onto an unexposed filter; lane 7, 10² P. carinii organisms spiked onto an unexposed filter; lane 8, positive control; lane 9, negative control.