Enhanced topical delivery of non-complexed molecular iodine for Methicillin-resistant Staphylococcus aureus decolonization

Molecular iodine is not responsible for cytotoxicity in iodophors

Background

Ten percent povidone-iodine (PVP-I) was initially promoted as ‘tamed iodine’ as the chemical activity of the active biocide, uncomplexed or free molecular iodine (I₂), is reduced 30- to 50-fold compared with Lugol's solution. The idea that I₂ is responsible for topical iodine staining and irritation remains widely held. However, there are no controlled studies that characterize the cytotoxicity and staining of the hydrophobic I₂ species compared with the other hydrophilic iodine species that comprise over 99.9% of the total iodine in topical iodine disinfectants.

Aims

To compare the staining properties of the I₂ species with other topical iodine disinfectants; to evaluate if the concentrations of I₂ in diluted PVP-I used to reduce severe acute respiratory syndrome coronavirus-2 in the nasal cavity are potentially cytotoxic; and to determine if high concentrations of I₂ can be delivered beyond the stratum corneum into the hypodermis, which could provide a mechanistic rationale for I₂ out-gassing.

Methods

Five liquid compositions that contained complexed and uncomplexed (free) I₂ in aqueous and non-aqueous carriers were used to evaluate the interaction of I₂ with mammalian cells in culture as well as human and pig skin.

Findings

Concentrations of I₂ (7800 ppm) that are 1500 times higher than that found in PVP-I can be applied to skin without irritation and staining. I₂ is not cytotoxic at concentrations >100 times higher than that found in PVP-I, and does not contribute materially to staining of skin at concentrations found in Lugol's solution (approximately 170 ppm). I₂ can partition into hypodermis tissue, remain there for hours and out-gas from skin. PVP-I and Lugol's solution are highly effective topical disinfectants, but do not facilitate diffusion of I₂ through the stratum corneum.

Conclusion

The maximum concentration of I₂ found in diluted PVP, approximately 25 ppm, is not cytotoxic or irritating. The potential clinical utility of I₂ has been limited by incorporating this broad-spectrum biocide into acidic aqueous formulations that contain numerous chemical species that contribute toxicity but not biocidal activity. I₂ can be delivered topically into hypodermis tissue without irritation.

Thermochromic Polyvinyl Alcohol-Iodine Hydrogels with Safe Threshold Temperature for Infectious Wound Healing

Iodophor (povidone-iodine) has been widely used for antibacterial applications in the clinic. Yet, limited progress in the field of iodine-based bactericides has been achieved since the invention of iodophor. Herein, a blue polyvinyl alcohol-iodine (PAI) complex-based antibacterial hydrogel is explored as a new generation of biocompatible iodine-based bactericides. The obtained PAI hydrogel maintains laser triggered liquefaction, thermochromic, and photothermal features for highly efficient elimination of bacteria. In vitro antibacterial test reveals that the relative bacteria viabilities of Escherichia coli (E.coli) and methicillin-resistant Staphylococcus aureus (MRSA) incubated with PAI hydrogel are only 8% and 3.8%, respectively. Upon single injection of the PAI hydrogel, MRSA-infected open wounds can be efficiently healed in only 5 days, and the healing speed is further accelerated by laser irradiation due to the dynamic interaction between iodine and polyvinyl alcohol, causing up to ∼29% of wound area being closed on day 1. In addition, a safe threshold temperature of skin scald (∼45 °C) emerges for PAI hydrogels because of thermochromic properties, avoiding thermal injuries during irradiation. In addition, no observed toxicity or skin irritation is observed for the PAI hydrogel. This work expands the category of iodine-based bactericides for safe and controllable management of infected wounds.

Freezing-Induced Simultaneous Reduction of Chromate and Production of Molecular Iodine: Mechanism, Kinetics, and Practical Implications

A new method for the concurrent treatment of Cr(VI)-contaminated wastewater and production of the useful I₂ chemical was developed. The method is based on the redox reaction between Cr(VI) and I^- that occurs when an aqueous wastewater solution containing Cr(VI) and I^- is frozen, producing I₂ and allowing for the effective removal of Cr. The redox reaction occurs primarily because of the accumulation of Cr(VI), I^-, and protons in the ice grain boundaries formed during freezing (i.e., the freeze concentration effect). This effect was verified by confocal Raman spectroscopy and the experiments varying I^- concentration and pH. The reduction of Cr(VI) (20 μM) was near complete after freezing at I^- concentrations ≥ 100 μM, pH ≤ 3.0, and temperatures ≤ -10 °C. The freezing method (liquid cooling vs air cooling) had little effect on the final Cr(VI) reduction efficiency but had a significant effect on the Cr(VI) reduction rate. The freezing method was also tested with Cr(VI)-contaminated electroplating wastewater samples, and simultaneous Cr(VI) reduction and I₂ production proceeded rapidly in a frozen solution but was not observed in an aqueous solution. Additionally, other substances in electroplating wastewater did not reduce the rate and final efficiency of Cr(VI) reduction and I₂ production. Therefore, the freezing/Cr(VI)/I^- system can be considered a feasible approach to water-energy nexus technology for simultaneous I₂ production and Cr(VI)-contaminated wastewater treatment.

Povidone Iodine: Properties, Mechanisms of Action, and Role in Infection Control and Staphylococcus aureus Decolonization

Nasal decolonization is an integral part of the strategies used to control and prevent the spread of methicillin-resistant Staphylococcus aureus (MRSA) infections. The two most commonly used agents for decolonization are intranasal mupirocin 2% ointment and chlorhexidine wash, but the increasing emergence of resistance and treatment failure has underscored the need for alternative therapies. This article discusses povidone iodine (PVP-I) as an alternative decolonization agent and is based on literature reviewed during an expert’s workshop on resistance and MRSA decolonization.

Nasal decolonization is an integral part of the strategies used to control and prevent the spread of methicillin-resistant Staphylococcus aureus (MRSA) infections. The two most commonly used agents for decolonization are intranasal mupirocin 2% ointment and chlorhexidine wash, but the increasing emergence of resistance and treatment failure has underscored the need for alternative therapies. This article discusses povidone iodine (PVP-I) as an alternative decolonization agent and is based on literature reviewed during an expert’s workshop on resistance and MRSA decolonization. Compared to chlorhexidine and mupirocin, respectively, PVP-I 10 and 7.5% solutions demonstrated rapid and superior bactericidal activity against MRSA in in vitro and ex vivo studies. Notably, PVP-I 10 and 5% solutions were also active against both chlorhexidine-resistant and mupirocin-resistant strains, respectively. Unlike chlorhexidine and mupirocin, available reports have not observed a link between PVP-I and the induction of bacterial resistance or cross-resistance to antiseptics and antibiotics. These preclinical findings also translate into clinical decolonization, where intranasal PVP-I significantly improved the efficacy of chlorhexidine wash and was as effective as mupirocin in reducing surgical site infection in orthopedic surgery. Overall, these qualities of PVP-I make it a useful alternative decolonizing agent for the prevention of S. aureus infections, but additional experimental and clinical data are required to further evaluate the use of PVP-I in this setting.

Liquid Exfoliation of Atomically Thin Antimony Selenide as an Efficient Two-Dimensional Antibacterial Nanoagent

The ever-growing global crisis of multidrug-resistant bacteria has triggered a tumult of activity in the design and development of antibacterial formulations. Here, atomically thin antimony selenide nanosheets (Sb₂Se₃ NSs), a minimal-toxic and low-cost semiconductor material, were explored as a high-performance two-dimensional (2D) antibacterial nanoagent via a liquid exfoliation strategy integrating cryo-pretreatment and polyvinyl pyrrolidone (PVP)-assisted exfoliation. When cultured with bacteria, the obtained PVP-capped Sb₂Se₃ NSs exhibited intrinsic long-term antibacterial capability, probably due to the reactive oxygen species generation and sharp edge-induced membrane cutting during physical contact between bacteria and nanosheets. Upon near-infrared laser irradiation, Sb₂Se₃ NSs achieved short-time hyperthermia sterilization because of strong optical absorption and high photothermal conversion efficiency. By virtue of the synergistic effects of these two broad-spectrum antibacterial mechanisms, Sb₂Se₃ NSs exhibited high-efficiency inhibition of conventional Gram-negative Escherichia coli, Gram-positive methicillin-resistant Staphylococcus aureus, and wild bacteria from a natural water pool. Particularly, these three categories of bacteria were completely eradicated after being treated with Sb₂Se₃ NSs (300 μM) plus laser irradiation for only 5 min. In vivo wound healing experiment further demonstrated the high-performance antibacterial effect. In addition, Sb₂Se₃ NSs depicted excellent biocompatibility due to the biocompatible element constitute and bioinert PVP modification. This work enlightened that atomically thin Sb₂Se₃ NSs hold great promise as a broad-spectrum 2D antibacterial nanoagent for various pathogenic bacterial infections.