Unraveling the antibacterial mode of action of a c

Authors: Sandra Carolina Londono Lynda B Williams

Publish Date: 2015/06/09

Volume: 38, Issue: 2, Pages: 363-379

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Abstract

Natural antibacterial clays can inhibit growth of human pathogens therefore understanding the antibacterial mode of action may lead to new applications for health The antibacterial modes of action have shown differences based on mineralogical constraints Here we investigate a natural clay from the Colombian Amazon AMZ known to the Uitoto natives as a healing clay The physical and chemical properties of the AMZ clay were compared to standard reference materials smectite SWy1 and kaolinite API 5 that represent the major minerals in AMZ We tested model Gramnegative Escherichia coli ATCC 25922 and Grampositive Bacillus subtilis ATCC 6633 bacteria to assess the clay’s antibacterial effectiveness against different bacterial types The chemical and physical changes in the microbes were examined using bioimaging and mass spectrometry of clay digests and aqueous leachates Results indicate that a single dose of AMZ clay 250 mg/mL induced a 4–6 order of magnitude reduction in cell viability unlike the reference clays that did not impact bacterial survival AMZ clay possesses a relatively high specific surface area 5123 m2/g and much higher total surface area 27882 m2/g than the reference clays In aqueous suspensions 50 mg clay/mL water soluble metals are released and the minerals buffer fluid pH between 41 and 45 We propose that the clay facilitates chemical interactions detrimental to bacteria by absorbing nutrients eg Mg P and potentially supplying metals eg Al toxic to bacteria This study demonstrates that native traditional knowledge can direct scientific studiesThis research was supported by the National Science Foundation Grant EAR 112393 to LW the Administrative Department of Science Technology and Innovation in Colombia Colciencias as well as the Clay Minerals Society and the Geological Society of America student Grants to SCL We thank Professor Rajeev Misra and Amisha PoretPeterson for their assistance and guidance in microbiology Thanks to David Lowry TEM Keith Morrison XRF Panjai Prapaipong Stephen Romaniello Gwyneth Williams ICPMS and John Mardinly EDS for their technical support at Arizona State University and Sharon Walker at UC Riverside for discussions of DLVO data We gratefully acknowledge the use of facilities within the LeRoy Eyring center for Solid State Science at Arizona State University The authors sincerely thank the late Vicente Makuritofe Uitoto cultural expert and his family for their collaboration and contribution to this workThe results of this study were communicated and explained to the Uitoto traditional authority from which the authors received the sample with permission to study it No monetary benefit has been generated and the clay is Uitoto’s property This study shows that certain culturalbased practices have a scientific basis

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