Low performance of Policimbac® broth microdilution in determining polymyxin B MIC for Klebsiella pneumoniae

Abstract

Klebsiella pneumoniae is a global threat to healthcare, and despite the availability of new drugs, polymyxins are still an important therapeutic option for this and other resistant gram-negative pathogens. Broth microdilution is the only method that is recommended for polymyxins. In this study, we evaluated the accuracy of a commercial Policimbac® plate in determining the polymyxin B MIC for K. pneumoniae clinical isolates. The results were compared with those of the broth microdilution method according to ISO 16782. The Policimbac® plate had an excellent 98.04% categorical agreement, but unacceptable 31.37% essential agreement rates. Almost 2% of major errors as observed. Additionally, 52.94% of the strains overestimated the MIC at 1 µg/mL. Three isolates were excluded from the analysis due to the drying of the Policimbac® plate. To avoid dryness, we included wet gauze for the test, obtaining a 100% of categorical agreement rate; however, a low essential agreement was maintained (25.49%). In conclusion, the Policimbac® plate was unable to correctly determine the polymyxin B MIC for K. pneumoniae isolates. This low performance may interfere with the clinical use of the drug and, thus, with the result of the patient’s treatment.

Challenges in the Detection of Polymyxin Resistance: From Today to the Future

“…This suggests that Policimbac ® was not as accurate in correctly identifying these strains when compared to the reference method. Therefore, despite the high overall sensitivity, the low performance in analytical specificity may be an obstacle to the appropriate clinical use of Policimbac ® in certain scenarios [ 19 ].…”