Antibiotic-resistant bacteria in surveillance stool cultures of patients with prolonged neutropenia

The value of stool surveillance for antibiotic-resistant gram-negative bacteria was analyzed in 86 neutropenic bone marrow transplant patients. Twice-weekly specimens were inoculated onto culture medium containing gentamicin plus carbenicillin. The recovered organisms were identified to the species level and tested for antibiotic susceptibility. Forty-eight resistant organisms were recovered from 35 patients. Thirteen isolates persistently colonized patients. Escherichia coli (29%) and Pseudomonas aeruginosa (19%) were the most frequently recovered organisms. Although most organisms were recovered while patients were on antibiotics, 15 isolates, including eight of nine resistant P. aeruginosa, were detected before antibiotics were initiated. The duration of antibiotic use was longer for patients persistently colonized than for those not colonized (P = 0.03). Of the 15 resistant organisms which caused infection, 12 were detected in the surveillance cultures. Infections by antibiotic-resistant organisms occurred more frequently in patients colonized than in those not colonized (p = 0.006) and more frequently in patients persistently colonized than in those colonized only once (P = 0.01). The absence of colonization or persistent colonization correlated well with the absence of infection (negative predictive values of 94 and 91%, respectively).