Immunity protein component of a toxin-immunity protein module, which functions as a cellular contact-dependent growth inhibition (CDI) system. CDI modules allow bacteria to communicate with and inhibit the growth of closely related neighboring bacteria in a contact-dependent fashion. Protects cells against the DNase activity of CdiA, its cognate toxin protein, but not against non-cognate CdiA from E.coli strain 536 / UPEC. Interacts with cognate CdiA-CT but not non-cognate CdiA-CT from E.coli strain 536 / UPEC. There are 2 cdiBAI loci in this strain, this is locus 2.