Reply to Dr. Kampf's letter

Abstract

To the Editor:First of all, we used EN 12054 (now EN 13727) to assess the most interesting products from the cytotoxicity study against the 2 organisms responsible for most serious hospital-acquired infections—methicillin-resistant Staphylococcus aureus (MRSA) and Clostridium difficile—which seemed more relevant to us than the recommended strains (Escherichia coli, Enterococcus hirae, Pseudomonos aeruginosa, S aureus). The neutralization step for the alcohol rubs was as per the recommended method (Ref 12). Xgel requires a calcium-rich environment for neutralization that is not provided by the usual neutralizers (eg, those for alcohol), hence the use of Ringer's solution, which is calcium rich. We showed that the neutralization protocol used was effective on MRSA, so it is at least valid for MRSA; we feel it would be very unlikely not to also work for spores of C difficile. The validation of neutralization is indeed important; it works, and, therefore, the results are not “potentially false positive” and should be regarded as valid.Second, the comment regarding the counts is valid. We agree that the handrub would contain 2×108 cells and that the neutralization step will contain 2×107. We cultured 0.1 mL of this so that we should have grown 2×106 colony-forming units if there was no kill. Because no colony-forming units were found with Xgel and MRSA or ACCB, there is at least a >106 log kill. Perhaps we should not have extrapolated back to 2×108 in the Figure, but, in any case, Xgel still easily passes the test. Third, we agree that the effect of Xgel on spores of C difficile (stored in 50% ethanol as mentioned in the Methods section—so definitely NOT vegetative cells) was remarkable. Our considered view, based on the reasonable assumption that the neutralization that was effective on MRSA was also effective on C difficile spores, is that the active component in Xgel, CuAL42, may be attaching to the surface of the spores and preventing growth when the spores germinate in culture. When time permits, we intend to test this hypothesis.Finally, clinical evidence is indeed relevant, and, in our initial testing with volunteer nurses from UCLH, there has been a unanimous preference for Xgel over Purell. To the Editor: First of all, we used EN 12054 (now EN 13727) to assess the most interesting products from the cytotoxicity study against the 2 organisms responsible for most serious hospital-acquired infections—methicillin-resistant Staphylococcus aureus (MRSA) and Clostridium difficile—which seemed more relevant to us than the recommended strains (Escherichia coli, Enterococcus hirae, Pseudomonos aeruginosa, S aureus). The neutralization step for the alcohol rubs was as per the recommended method (Ref 12). Xgel requires a calcium-rich environment for neutralization that is not provided by the usual neutralizers (eg, those for alcohol), hence the use of Ringer's solution, which is calcium rich. We showed that the neutralization protocol used was effective on MRSA, so it is at least valid for MRSA; we feel it would be very unlikely not to also work for spores of C difficile. The validation of neutralization is indeed important; it works, and, therefore, the results are not “potentially false positive” and should be regarded as valid. Second, the comment regarding the counts is valid. We agree that the handrub would contain 2×108 cells and that the neutralization step will contain 2×107. We cultured 0.1 mL of this so that we should have grown 2×106 colony-forming units if there was no kill. Because no colony-forming units were found with Xgel and MRSA or ACCB, there is at least a >106 log kill. Perhaps we should not have extrapolated back to 2×108 in the Figure, but, in any case, Xgel still easily passes the test. Third, we agree that the effect of Xgel on spores of C difficile (stored in 50% ethanol as mentioned in the Methods section—so definitely NOT vegetative cells) was remarkable. Our considered view, based on the reasonable assumption that the neutralization that was effective on MRSA was also effective on C difficile spores, is that the active component in Xgel, CuAL42, may be attaching to the surface of the spores and preventing growth when the spores germinate in culture. When time permits, we intend to test this hypothesis. Finally, clinical evidence is indeed relevant, and, in our initial testing with volunteer nurses from UCLH, there has been a unanimous preference for Xgel over Purell. Are the conclusions on a copper-based biocidal handrub scientifically justified?American Journal of Infection ControlVol. 37Issue 8PreviewTo the Editor: Full-Text PDF