I have read that a bridge/switch can be used to increase the number of collision domains in the network, but somewhere I also read that a bridge reduces collision domains. Is it possible for bridge to reduce a collision domain?
A bridge (a switch is a high-density bridge) can help reduce the number of devices in a collision domain by breaking a single collision domain into multiple, separate collision domains with fewer devices on each collision domain than were on the original collision domain.
Each interface on a bridge is a separate collision domain. Assuming you were replacing a hub, where every interface is in the same collision domain, with a switch. Suddenly, you have more collision domains, but there are less devices on each collision domain than were on the original collision domain.