FIG. 1.

Ethidium bromide-stained agarose gel showing pla PCR results for samples of individual O. hirsuta collected from Applewood Estates, Colo. Large bands represent a 478-bp fragment amplified from the Y. pestis pla gene. Lane 1, molecular size marker; lane 2, positive control (A1122); lanes 3 and 8, negative controls; lanes 4 to 7 and 9 to 12, flea samples (4, 5, and 10 are positive; 6, 7, 9, 11, and 12 are negative). Note: The high-molecular-weight DNA at the top of the gel is probably flea DNA in that it appears only in the lanes containing PCR samples from flea suspensions.