PFGE pattern of ESBL-positive isolates from flock B. (A) Comparison of Escherichia coli isolates from the parent flock and the outer surface of four eggs at the time of arrival at the hatchery. Isolates were of phylogroup B1 and harbor a CTX-M1 gene. Lane M, Salmonella Braenderup H9812; lanes 1 and 12, feces sample 2, parent flock; lanes 2 and 9, surface egg 4; lanes 3 and 7, feces sample 3, parent flock; lanes 4 and 13, boot swab, parent flock; lanes 5 and 10, surface egg 3; lane 6, surface egg 1; lane 8, feces sample 1, parent flock; lane 11, surface egg 2. (B) Comparison of phylogroup-negative Escherichia fergusonii isolates which were positive for the TEM-52 gene. Samples were taken from the parent flock and at the hatchery after disinfection of the eggs. Lane M, Salmonella Braenderup H9812; lane 1, feces sample 3, parent flock; lane 2, feces sample 2, parent flock; lane 3, feces sample 1, parent flock; lane 4, boot swap, parent flock; lane 5, surface egg 5.