Iodine-lithium-alpha-dextrin (ILαD) against Staphylococcus aureus skin infections: a comparative study of in-vitro bactericidal activity and cytotoxicity between ILαD and povidone-iodine

Background: As antimicrobial resistance continues to increase, revisiting old antimicrobial agents, modified to enhance efficacy and safety, becomes important. Iodine has been widely used for more than 150 years as a wound and skin disinfectant; it is an effective broad range bactericide and does not promote the development of resistant strains. The most important iodine-based agent is povidone-iodine (PVP-I) which provides excellent antibacterial activity. However, its safety profile has been questioned. Aim: To evaluate the in-vitro antibacterial efficacy and kinetic properties of a novel iodine-based compound, iodine lithium alpha-dextrin (IL alpha D), against Staphylococcus aureus, and compare the in-vitro cytotoxicity profiles of IL alpha D and PVP-I. Methods: A minimum inhibitory concentration (MIC) microbroth dilution method was performed against 12 meticillin-resistant (MRSA) and eight meticillin-susceptible (MSSA) S. aureus clinical isolates using IL alpha D and PVP-I. Time-kill and post-antibiotic effect studies of IL alpha D provided rate-of-kill information. MTT cytotoxicity assays were performed using three cell lines, treated with MIC doses of ILaD and PVP-I. Findings: The MIC values of IL alpha D and PVP-I against the MRSA strains were 125 mg/L and 31.25 mg/L, respectively. Time-kill and post-antibiotic effect studies of IL alpha D revealed a log10 reduction factor of 3 within 8 h of exposure at a 2 x MIC dose; the post-antibiotic effect was calculated at 5 +/- 0.3h. Cell viability was affected slightly at the MIC dose of IL alpha D, while the MIC dose of PVP-I exerted a strong cell growth inhibitory effect of 90-95%. Conclusions: IL alpha D could be a promising solution against staphylococcal infections as it is effective, does not promote the development of resistant strains, and in-vitro testing indicates that it may be safer than PVP-I. Further studies are justified to determine whether IL alpha D overcomes the clinical limitations of PVP-I. (C) 2017 The Healthcare Infection Society. Published by Elsevier Ltd. All rights reserved.