This chapter discusses special considerations required when treating selected bacterial infections (anaerobic, atypical mycobacterial, Brucella, leptospirosis, mycoplasma, and Nocardia). The selection of antimicrobial agents for the empirical treatment of pure or mixed anaerobic infections is often based on surveillance data at the local or national level. Many anaerobic bacterial infections are mixed, but attempted elimination of all the organisms may not be necessary. This is because the unique synergism that sometimes occurs between aerobic and anaerobic bacteria is such that elimination of only some of the species present in the mixed bacterial infection will result in removal of the synergistic effect and clearance of the infection. The two major approaches to the treatment of anaerobic infections are appropriate antimicrobial therapy and surgical management.