Antimicrobials Are a Photodynamic Inactivation Adjuvant for the Eradication of Extensively Drug-Resistant Acinetobacter baumannii.

Agata Wozniak,Mariusz Grinholc,Aleksandra Rapacka-Zdonczyk,Nico T Mutters

doi:10.3389/fmicb.2019.00229

Abstract

The worldwide emergence of extensively drug resistant (XDR) Acinetobacter baumannii has reduced the number of antimicrobials that exert high bactericidal activity against this pathogen. This is the reason why many scientists are focusing on investigations concerning novel non-antibiotic strategies such as antimicrobial photodynamic inactivation (aPDI) or the use of antimicrobial blue light (aBL). Therefore, the aim of the current study was to screen for antimicrobial synergies of routinely used antibiotics and phototherapies, including both aPDI involving exogenously administered photosensitizing molecules, namely, rose bengal, and aBL, involving excitation of endogenously produced photoactive compounds. The synergy testing was performed in accordance with antimicrobial susceptibility testing (AST) standards, including various methodological approaches, i.e., antibiotic diffusion tests, checkerboard assays, CFU counting and the evaluation of postantibiotic effects (PAEs). We report that combining antimicrobials and aPDI/aBL treatment led to a new strategy that overcomes drug resistance in XDR A. baumannii, rendering this pathogen susceptible to various categories of antibiotics. Sublethal aPDI/aBL treatment in the presence of sub-MIC levels of antimicrobials effectively killed A. baumannii expressing drug resistance to studied antibiotics when treated with only antibiotic therapy. The susceptibility of XDR A. baumannii to a range of antibiotics was enhanced following sublethal aPDI/aBL. Furthermore, 3′-(p-aminophenyl) fluorescein (APF) testing indicated that significantly increased reactive oxygen species production upon combined treatment could explain the observed synergistic activity. This result represents a conclusive example of the synergistic activity between photodynamic inactivation and clinically used antimicrobials leading to effective eradication of XDR A. baumannii isolates and indicates a potent novel therapeutic approach.

Highlights

Acinetobacter baumannii is a threatening human pathogen
Photoinactivation of microorganisms can damage the cell envelope, genetic material or both simultaneously (Grinholc et al, 2015); in the present study, we focused on analyzing whether the synergistic effect between antimicrobial photodynamic inactivation (aPDI)/antimicrobial blue light (aBL) and antimicrobials occurs and whether it is influenced by the administration of an exogenous PS such as rose bengal (RB) or of endogenously produced PSs such as porphyrins, which we excited with very intense blue light
To meet the international standards for synergy testing, numerous official Antimicrobial Susceptibility Testing (AST) procedures were employed to ensure that reliable conclusions were drawn; we introduce a general workflow diagram to facilitate following the obtained results (Figure 1)

Summary

Introduction

Acinetobacter baumannii is a threatening human pathogen. A key component of its pathogenicity is its outstanding capability to acquire resistance (Spellberg and Bonomo, 2014). A lack of effective antimicrobials has forced the need for the development of novel strategies to control A. baumannii infections One of these approaches is antimicrobial photodynamic inactivation (aPDI) or antimicrobial blue light (aBL) (Nitzan et al, 1998; Dai et al, 2009; Cai et al, 2012; Huang et al, 2014; Yuan et al, 2017; Yang et al, 2018). These strategies exert high bactericidal efficacy toward various microbes regardless of antibiotic resistance. In the presence of oxygen, light induces the formation of reactive oxygen species (ROS) by energy or electron transfer from the PS excited state; these ROS can oxidize numerous cell biomolecules, leading to bacterial killing (Grinholc et al, 2015)

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