Transmission electron microscopy.

C. jejuni strains were resuspended from MH agar into PBS, pelleted for 3 min at 13,200 rpm in a microcentrifuge, resuspended in 2% glutaraldehyde in 0.1 M cacodylate, and then incubated on ice for 1 h. Copper-coated Formvar grids were negatively glow discharged, and bacterial samples were then applied to the grids. The samples were stained with 2% uranyl acetate and visualized with an FEI Tecnai G2 Spirit BioTWIN transmission electron microscope. Flagellar numbers were determined from at least 100 individual cells and averaged from two biological replicates to determine the proportion of bacterial populations producing different flagellation phenotypes, as follows: hyperflagellated (a bacterium producing two or more flagella at one or both poles), wild type (producing a single flagellum at each pole or a flagellum at one pole with the other pole aflagellated), or aflagellated (lacking a flagellum). For analysis of cell body lengths, bacterial cell bodies from electron micrographs were visualized, measured using the ImageJ software, and placed into one of the following four categories: <0.5 μm (minicells), 0.5 to 1 μm, 1 to 2 μm, and >2 μm. After averaging, the standard deviation for each population was calculated.