Gram-negative bacilli occur in 10% of such infections, usually with open fractures and hospital-acquired infection. Polymicrobial, or mixed, infections (25%-30%) are actually more common, and may require prolonged, complex treatment.
Remember that an organism initially present may be replaced, or joined, by other bacteria during treatment, adding to the challenge of correct antibiotic selection.
Antibiotics are a valuable adjunct to the surgical treatment of post-traumatic infections. However, the overriding principle is that adequate clearance of all infected and nonviable tissue is the most important factor. Macroscopic quantities of planktonic and biofilm bacteria are reduced by surgical removal– so-called bioburden reduction. Antibiotic administration suppresses bacterial growth and helps to eliminate any residual bacteria at the cellular level.
Unless a patient is septic, with a life-threatening infection, it is desirable to obtain culture specimens before beginning antibiotics, in order to maximize the likelihood of correct identification and sensitivity-testing of bacterial pathogens.