Discoveries associated with antibacterial activity of hydrated
clays necessitate assessments of in vivo efficacy, practical use and safety. Surface properties of
clays can lead to variations in the composition and abundance of bound compounds or
ions, thus affecting antibacterial activity. Since exchangeable
metal ions released from the
clay surface are responsible for in vitro antibacterial activity, we evaluated the in vivo antibacterial efficacy of four natural
clays (one
illite clay, two
montmorillonite clays and one
kaolinite clay) and three ion-exchanged, antibacterial
clays against superficial, cutaneous
meticillin-resistant Staphylococcus aureus (MRSA)
infections in mice. Superficial, cutaneous
wounds on the back of SKH1-Elite mice were generated and subsequently infected with MRSA. Following twice daily applications of a hydrated
clay poultice to infected
wounds for 7 days, we observed significant differences in the in vivo antibacterial efficacy between different types of
clays. The natural and ion-exchanged
illite clays performed best, as measured by bacterial load, inflammatory response and gross
wound morphology with significant decreases in bacterial viability and
dermatitis. Topical application of
kaolinite clay was the least effective, resulting in the lowest decrease in bacterial load and exhibiting severe
dermatitis. These data suggest that specific types of
clays may offer a complementary and integrative strategy for topically treating MRSA and other cutaneous
infections. However, since natural
clays exhibit in vitro antibacterial variability and vary vastly in surface chemistries, adsorptive/absorptive characteristics and structural composition, the properties and characteristics of
illite clays could aid in the development of standardized and customized aluminosilicates for topical
infections.