FIG. 1.

(A) Experimental design: sheep blood agar plate with two halves separated by an Anopore membrane embedded in the agar to create a barrier. To prevent swarming bacteria from bypassing the membrane, amoxicillin-clavulanate tablets (ut, upper tablet; lt, lower tablet) were placed at the ends of the Anopore membrane (vertical line). Two inoculation points for the first strain (ip1) and one inoculation point for the second strain (ip2) are indicated. (B) Two nonidentical strains were inoculated on one side of the Anopore membrane, and after swarming a Dienes line formed perpendicular to the membrane on the left side of the membrane. On the other side of the membrane one of the two strains was inoculated and was able to swarm right up to the membrane. Due to the illumination conditions the vertical Anopore membrane cast a shadow on both sides (S); this does not indicate reduced growth near the barrier. The upper antibiotic tablet is at position ut, and the lower antibiotic tablet is just below position lt.