It depends on the pathogen and localization of infection. Broadly speaking broad-spectrum antibiotics must be used in ICU like 3rd or 4th generation cephalosporines, broad-spectrum penicillins (piperacillin-tazobactam, ticarcillin-clavulanate), Vancomicin, Linezolid (against MRSA), anti-psudomonic antiboitic (ceftazidime, fluoroquinolones, cefepime), carbapenems (imipenem, ertapenem), Aztreonam ecc. The real deal is to de-scalate antibiotic treatment in order to reduce resistence rates and adverse effects of antiboitic drugs.