Researchers in the late 1950s isolated multiple antibiotic-resistant strains of the bacterium Shigella, which causes dysentery. Such resistance was caused by nonchromosomal R factors that originated in E. coli. Which of the following forms of extrachromosomal heredity-maternal effect, organelle heredity, infectious heredity-would you consider most closely related to the transfer bacterial antibiotic-resistant strains?