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Susceptibility testing of bacteria recovered from patients with peritonitis complicating continuous ambulatory
H Ludlam1, L Johnston, P Hopkins
1Department of Medical Microbiology, St. Bartholmew's Hospital, West Smithfield, London, United Kingdom.
Abstract:
Antagonism of antibiotic activity by peritoneal dialysate has been postulated to be a cause of failure of treatment of peritonitis complicating continuous ambulatory peritoneal dialysis. We evaluated by a case-control study whether unexpected treatment failure could be attributed to such antagonism. Bacteria isolated from 34 patient episodes of peritonitis treated with the same regimen of ciprofloxacin monotherapy were studied. Ciprofloxacin was significantly less active in dialysate than in Iso-Sensitest broth (IB). The median MIC in IB was 0.5 microgram/ml, increasing to 2.0 micrograms/ml for both fresh dialysate (FD) (P = 0.003) and pooled dialysis effluent (PDE) (P = 0.03); the median MBC in IB was 8.0 micrograms/ml, increasing to 128.0 micrograms/ml in FD (P = 0.0002) and 64.0 micrograms/ml in PDE (P = 0.02). However, no significant differences were found in the results for patients suffering unexpected treatment failure (relapse of peritonitis) compared with the results for patients whose infection resolved without sequel. In IB the median MICs for relapsers and nonrelapsers were 1.0 and 0.5 microgram/ml, respectively (P = 0.88); median MBCs were 32.0 and 4.0 micrograms/ml (P = 0.19). In FD median MICs for relapsers and nonrelapsers were 2.0 and 1.0 micrograms/ml (P = 0.06); median MBCs were 128.0 micrograms/ml for both groups (P = 0.84). In PDE the median MICs were 2.0 micrograms/ml for both groups (P = 0.78); median MBCs were 256.0 and 64.0 micrograms/ml (P = 0.17). We therefore found no evidence to suggest that antagonism of antibiotic activity by dialysate is a cause of treatment failure or that conventional methods for laboratory susceptibility testing in peritonitis complicating continuous ambulatory peritoneal dialysis should be abandoned in favor of testing in media containing dialysate.
Insights
Peritoneal dialysis fluid reduces antibiotic effectiveness, but this study found no evidence it causes treatment failure in peritonitis. Standard laboratory testing for antibiotic susceptibility remains reliable for continuous ambulatory peritoneal dialysis patients.
Area of Science:
- Nephrology
- Infectious Diseases
- Clinical Microbiology
Background:
- Peritonitis is a serious complication of continuous ambulatory peritoneal dialysis (CAPD).
- Reduced antibiotic activity in peritoneal dialysate has been suspected as a cause of treatment failure in CAPD peritonitis.
- Ciprofloxacin is a common monotherapy for CAPD peritonitis.
Purpose of the Study:
- To investigate if antagonism of ciprofloxacin activity by peritoneal dialysate contributes to treatment failure in CAPD peritonitis.
- To determine if standard laboratory susceptibility testing methods are adequate for CAPD peritonitis.
Main Methods:
- A case-control study was conducted on bacteria from 34 CAPD peritonitis episodes treated with ciprofloxacin.
- Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) of ciprofloxacin were determined in Iso-Sensitest broth (IB), fresh dialysate (FD), and pooled dialysis effluent (PDE).
- Antibiotic activity was compared between patients with treatment failure (relapse) and those who resolved without sequelae.
Main Results:
- Ciprofloxacin exhibited significantly reduced activity in FD and PDE compared to IB (P < 0.05).
- Median MIC increased from 0.5 µg/ml in IB to 2.0 µg/ml in FD and PDE.
- Median MBC increased from 8.0 µg/ml in IB to 64.0-128.0 µg/ml in FD and PDE.
- No significant differences in ciprofloxacin MIC or MBC were observed between relapsers and non-relapsers in any tested medium.
Conclusions:
- Dialysate antagonizes ciprofloxacin activity, but this antagonism does not appear to be a cause of treatment failure in CAPD peritonitis.
- Conventional laboratory susceptibility testing methods are likely sufficient and do not need to be replaced with testing in dialysate-containing media.
- Further research may explore other factors contributing to treatment failure in CAPD peritonitis.