Relationship between ceftriaxone use and resistance to third-generation cephalosporins among clinical strains of Enterobacter cloacae

Objective: To investigate the potential correlation between the use of extended-spectrum cephalosporins (ESCs) and resistance to this antibiotic class among clinical isolates of Enterobacter cloacae in a university-affiliated hospital. Materials and methods: Data on antimicrobial resistance and antimicrobial use concerning E. cloacae and ESCs were collected over a 4 year period. Various statistical tools were used to explore the potential relationship. Results: From 1999 to 2002, the proportion of E. cloacae isolates resistant to ESCs increased from 24.3% to 29.6%. (P=0.04), and the quantity of ESCs prescribed and given did not change. Within the subclass constituted by first-line ESCs, the proportion of ceftriaxone increased from 64.3% to 77.6% and the proportion of cefotaxime decreased accordingly, from 35.7% to 22.4%. Statistical analyses showed that E. cloacae resistance to ESCs correlated with ceftriaxone use regardless of the other ESCs. For every defined daily dose of ceftriaxone per 1000 patient days used in our hospital, resistance of E. cloacae isolates to ESCs increased by 1.36%. Conclusion: This study demonstrates a specific correlation between ceftriaxone use and the development of resistance in E. cloacae clinical isolates. The high biliary elimination of ceftriaxone compared with other ESCs may be responsible for a greater impact of this antibiotic on the digestive flora.