Extensively drug resistant Pseudomonas aeruginosa keratitis outbreak strain: virulence mechanisms and mitigation

Project Summary / Abstract The recent outbreak of keratitis caused by an extensively drug-resistant (XDR) strain of Pseudomonas aeruginosa with blaVIM-80 and blaGES-9 associated with preservative free artificial tears is concerning because the infecting bacteria was resistant to all tested antibiotics currently used to treat bacterial keratitis. As of May 2023 the CDC and other health departments had reported 81 patients in 18 states infected with this strain. Of these, 14 cases of vision loss associated with this infection had been recorded (a rate of 17.3%), including four cases of enucleation. Of great concern is that four patients have died within 30 days of culture collection. This progression to loss of the globe secondary to keratitis is extremely atypical as microbial keratitis rarely progresses to endophthalmitis. For instance, only 0.5% of microbial keratitis cases resulted in endophthalmitis in a recent large-scale study. In addition, our preliminary data, based on whole genome sequencing of the outbreak strain, in vitro antibiotic susceptibility testing, and rabbit keratitis studies, suggests that this strain has unique qualities that contribute to its pathogenesis. This includes extremely high resistance to standard of care antibiotics, the ability to survive and proliferate beyond typical strains in vivo, and an unusual virulence factor armament. The outbreak isolate groups phylogenetically with “cytotoxic” strains, but lacks type III secretion system (T3SS) toxins associated with cytotoxic or invasive strains. Such atypical strains that lack T3SS toxins represent 25% of keratitis isolates, yet have not been studied to investigate other virulence mechanisms that they employ. Because of the critical threat to vision caused by this strain and the lack of a good treatment approach, the objective of this study is to identify the mechanisms underlying the enhanced virulence of the outbreak strain, and to develop better therapeutic approaches to treat ocular infections caused by this XDR P. aeruginosa strain. The long-term objective is to generate mechanistic and translational information that can lead to antivirulence and antibiotic strategies in order to save vision from infections caused by this and future highly drug resistant bacterial infections of the eye. A major goal of this study will be to systematically test these and other candidate virulence factors unique to this outbreak strain in establishing keratitis and keratitis outcomes (Aim 1). A second goal will be to mitigate the threat of this strain by testing FDA approved antimicrobials and combinations not currently used in the eye (Aim 2). Based on our intriguing preliminary data and the impetus of this new pathogenic threat, we are poised to test the hypothesis that this outbreak strain is a new type of keratitis-causing P. aeruginosa, neither classically cytotoxic or invasive, that uses different virulence factors to establish infection. This study can have long-term impacts on the field by 1) providing information to help uncover why this strain concerningly appears to have the ability to spread from the cornea to deeper ocular tissues and cause life threatening systemic infections that can inform future anti-virulence strategies, and 2) development of more effective ocular antibiotic formulations that could be used to treat XDR bacterial infections. Furthermore, our team is uniquely situated to make rapid advances in understanding this form of keratitis based on our experience and having an active animal model of this disease demonstrating our ability to discern clinically relevant differences in virulence and antibiotic efficacy.