Alteration of staphylococcal flora in cardiac surgery patients receiving antibiotic prophylaxis.

The changes in staphylococcal flora induced by antibiotic prophylaxis with rifampin and nafcillin in combination among patients undergoing cardiac valve surgery were compared to those in patients undergoing coronary artery bypass surgery concurrently, who received only cefazolin. Rifampin-nafcillin prophylaxis eradicated carriage of Staphylococcus aureus at a significantly higher rate than did cefazolin (eradicated carriage of 89% vs. 48%, respectively; P less than 0.01); however, by the seventh postoperative day, 75% of the patients receiving rifampin and nafcillin had rifampin-resistant, coagulase-negative staphylococcal perianal floras, compared to 19% of those who received cefazolin (P less than 0.001). Patients receiving rifampin-nafcillin were colonized as frequently (66%) with coagulase-negative staphylococci resistant to gentamicin and methicillin as were those receiving cefazolin (68%). Patients in the coronary intensive care unit who received no antibiotics were infrequently colonized with either rifampin-resistant (none) or gentamicin- and methicillin-resistant (11%) staphylococci. Antibiotic prophylaxis may, therefore, be an important factor in perpetuating the hospital reservoir for antibiotic-resistant, coagulase-negative staphylococci.