Abdominal abscess

Community-acquired intra-abdominal infection
Aerobes	Anaerobes	Healthcare-associated intra-abdominal infection
Escherichia coli	Bacteroides	Staphylococcus epidermidis/aureus
Klebsiella pneumoniae	Clostridium	Pseudomonas aeruginosa
Proteus mirabilis	Peptostreptococcus	Enterococcus
Streptococcus	Fusobacterium	Enterobacter
Enterococcus	Prevotella

The general consensus on antimicrobials is to “hit hard and early,” meaning start broad-spectrum antibiotics immediately, and quickly narrow the antibiotics after cultures have returned. The choice of antibiotics depends on whether the infection is community-acquired or healthcare-associated. In some instances, an antifungal is needed. There are several antimicrobial choices available to treat intra-abdominal infections. Many can be treated with a single agent (Table 55.2). Methicillin-resistant Staphylococcus aureus (MRSA) is found in some intra-abdominal infections and should be treated with vancomycin. Linezolid, daptomycin, quinupristin–dalfopristin, and tigecycline also provide adequate coverage for MRSA. Empiric treatment of VRE is not recommended unless the patient is at very high risk for an infection due to this organism (such as a liver transplant patient with infection from the biliary tree) or is known to be colonized with VRE; this organism is usually sensitive to linezolid, quinupristin–dalfopristin, daptomycin, and ampicillin. Antifungal therapy is recommended if Candida is grown from intra-abdominal cultures. Fluconazole is appropriate for treatment of Candida albicans, but an echinocandin (caspofungin, micafungin) should be used for fluconazole-resistant Candida species such as Candida globrata or Candida tropicalis (Table 55.3