If a bacterium regenerates from an endospore that did not possess any of the plasmids that were contained in its original parent cell, the regenerated bacterium will probably also lack .

Explanation:

Most of the   bacterium contains plasmid. As given, if   bacterium regenerates from an endospore that did not possess any of the plasmids so the generated bacterium also lack antibiotic resistant genes.

Plasmid are circular form of extra chromosomal DNA that contain genes for   antibiotic resistant and genes for conjugation , and also for many other roles.

Plasmid replicate independently of the chromosomal DNA, and can be many in number. If the  bacterium lacks plasmid so these bacterium also lack antibiotic resistant genes.