White and blue light induce reduction in susceptibility to minocycline and tigecycline in Acinetobacter sp. and other bacteria of clinical importance

Abstract

Minocycline (MIN) and tigecycline (TIG) are antibiotics currently used for treatment of multi-drug resistant nosocomial pathogens. In this work, we show that blue light, as well as white light, modulate susceptibility to these antibiotics in a temperature-dependent manner. The modulation of susceptibility by light depends on the content of iron, resulting an increase in iron in a reduction in antibiotic susceptibility both under light as well as in the dark, though the effect was more pronounced in the latter condition. We further provide insights into the mechanism by showing that reduction in susceptibility to MIN and TIG induced by light is likely triggered by the generation of 1O2, which, by an yet unknown mechanism, would ultimately lead to the activation of resistance genes such as those coding for the efflux pump AdeABC. The clinical relevance of these results may rely in surface-exposed wound infections, given the exposure to light in addition to the relatively lower temperatures recorded in these type or lesions. We further show that the modulation of antibiotic susceptibility not only occurs in A. baumannii but also in other microorganisms of clinical relevance such as Escherichia coli or Staphylococcus aureus. Overall, our findings allow us to suggest that MIN and TIG antibiotic treatments may be improved by the inclusion of an iron chelator, a condition that in addition to keeping the wounds in the dark would increase the effectiveness in the control of infections involving these microorganisms.