Relationships between antimicrobial use and antimicrobial resistance in P. aeruginosa in an intensive care burn department

Increasing resistance in P. aeruginosa to multiple antibiotics has been observed and is posing therapeutic dilemmas. Antibiotic utilization is one factor that has been associated with the emergence of antimicrobial resistance.

We examined the relationships between annual antibiotic use and the incidence of resistance of P. aeruginosa isolates within the burned patients admitted to our intensive care department in order to direct measurements of control.

During a 5-year period (1 January 2000-31 December 2004), 203 nonrepetitive strains of P. aeruginosa were isolated from different specimens. Antimicrobial susceptibility testing has been carried out by the disk diffusion method according to the French Society of Microbiology. We studied the consumption of the following antibiotics: imipenem, ceftazidime, ciprofloxacin and amikacin. We measured antibiotic consumption with the antimicrobial density (AD), which takes into account the quantity of antibiotics in grams converted to daily doses dispensed and the number of patient-days in hospital. The defined daily dose was defined according to the World Health Organisation. Statistical analysis was conducted to explore the relationships between antibiotic use and the susceptibility patterns of P. aeruginosa. SPSS software was used to calculate the Spearman rank correlation coefficient. Statistical significance was defined as P < 0.05 for the corresponding correlation coefficients.

The consumption of ceftazidime showed no association with resistance to this drug. There were statistically significant relationships between increasing use of ciprofloxacin and incidence of resistant P. aeruginosa to this antibiotic (r s = 0.89, P = 0.05). In addition to the association between ciprofloxacin use and resistance to the drug itself, our study revealed a significant correlation between ciprofloxacin consumption and resistance to imipeneme (r s = 0.89, P = 0.043). A restriction of the use of ciprofloxacin was taken during 2003 and 2004; this was followed by a significant decrease of incidence of resistance in P. aeruginosa. The consumption of amikacin had no apparent association with resistance in P. aeruginosa to this drug.

Our data support a major role for ciprofloxacin in the emergence of multiresistance in P. aeruginosa. The use and/or duration of treatment with this antibiotic should be restricted as part of efforts to control the emergence of multidrug-resistant P. aeruginosa.