Susceptibility testing for bovine respiratory and enteric disease.
The interpretation of susceptibility results for antimicrobials with NCCLS-approved veterinary-specific breakpoints and where the methods also were NCCLS-approved are well established. When these same breakpoints are applied to other applications, however, the interpretation is not so clear. In these cases, a finding of S based on serial-dilution breakpoints puts the isolate in a defined population of bacteria with an MIC equal to or below the S breakpoint. An R result, in these cases, indicates that the organism may have an MIC equal to or greater (with no limits) than the R breakpoint. Extended-dilution testing yields more specific information about the isolate MIC. The relationship of disk-diffusion zone diameters to serial-dilution MICs is correlated on the basis of specific bacterial populations. When disk-diffusion results are interpreted for isolates other than those used for interpretive criteria development, the clinician is left wondering if the zone-diameter results now have a different relationship to serial-dilution results. Furthermore, the question of predictive value of the serial-dilution break-points still remains. The veterinary clinician should be aware of the differences in susceptibility testing predictive value for different applications. When approved veterinary-specific interpretive criteria are not available, then it is appropriate to keep records of clinical response related to susceptibility testing results for common therapies. Advice should be sought on the relationship of pathogen MICs to pharmacokinetic-pharmacodynamic parameters in these situations.
Apley
Michael D
MD
Department of Veterinary Diagnostic and Production Animal Medicine, Iowa State University, 1722 College of Veterinary Medicine, Christensen Drive, Ames, IA 50011-1250, USA. apley@iastate.edu
D000818:Animals; D000900:Anti-Bacterial Agents / Q000493:pharmacokinetics / Q000494:pharmacology*; D001419:Bacteria / Q000187:drug effects*; D002417:Cattle; D002418:Cattle Diseases / Q000188:drug therapy* / Q000382:microbiology; D015169:Colony Count, Microbial; D024881:Drug Resistance, Bacterial; D007410:Intestinal Diseases / Q000188:drug therapy / Q000382:microbiology / Q000662:veterinary; D008826:Microbial Sensitivity Tests / Q000379:methods / Q000662:veterinary*; D011237:Predictive Value of Tests; D012141:Respiratory Tract Infections / Q000188:drug therapy / Q000382:microbiology / Q000662:veterinary; D016896:Treatment Outcome
D000900:Anti-Bacterial Agents