The Infected Bat was a large bat that mutated after a secondary t-Virus infection. It can summon other Bats nearby via a piercing screech.
One of these bats was created shortly after the resurrection of James Marcus and his subsequent viral contamination of the Umbrella Research Center, where it inhabited the Church located above the facility's laboratory. This bat was killed by Rebecca Chambers and Billy Coen as the pair explored the church. The bat was quite large and could easily grab and fly around with either one of them. After being defeated, the bat died in the church allowing Billy and Rebecca to proceed.