Complex sentence: Their effectiveness is less affected by many common mechanisms of antibiotic resistance than other beta lactams and they are therefore especially useful for the treatment of infections caused by bacteria that are known or suspected to be multi-drug resistant.
Split into simpler sentences: Their effectiveness is less affected by many common mechanisms of antibiotic resistance than other beta lactams. They are therefore especially useful for the treatment of infections caused by bacteria that are known or suspected to be multi-drug resistant.