Clinical Features and Treatment Outcomes of Carbapenem-Resistant Pseudomonas aeruginosa Keratitis

Key Points

Question

What clinical features of multidrug-resistant Pseudomonas aeruginosa (VIM-GES-CRPA) keratitis are associated with use of artificial tears and outcomes following rose bengal–photodynamic antimicrobial therapy (RB-PDAT)?

Findings

In this case series of 9 patients, molecular profiling of VIM-GES-CRPA was crucial for identifying novel gene combinations as an alternative to antibiotic treatments, as exoU–positive strains may be associated with increased antibiotic resistance and poorer outcomes. In vitro and in vivo efficacy of RB-PDAT against these isolates suggest its potential as a therapy for managing recalcitrant infections.

Meaning

These findings suggest the need for novel therapeutics such as RB-PDAT for multidrug-resistant infections associated with the use of unpreserved ophthalmic drops.

This case series describes the clinical course, outcomes, and microbiological diagnostic profiles of multidrug-resistant Pseudomonas aeruginosa keratitis and the use of rose bengal–photodynamic antimicrobial therapy as an alternative or adjunctive therapy to treat isolates.

Abstract

Importance

Evaluation of the microbiological diagnostic profile of multidrug-resistant Pseudomonas aeruginosa keratitis and potential management with rose bengal–photodynamic antimicrobial therapy (RB-PDAT) is important.

Objective

To document the disease progression of carbapenemase-resistant P aeruginosa keratitis after an artificial tear contamination outbreak.

Design, Setting, and Participants

This retrospective observation case series included 9 patients 40 years or older who presented at Bascom Palmer Eye Institute and had positive test results for multidrug-resistant P aeruginosa keratitis between January 1, 2022, and October 31, 2023.

Main Outcomes and Measures

Evaluation of type III secretion phenotype, carbapenemase-resistance genes blaGES and blaVIM susceptibility to antibiotics, and in vitro and in vivo outcomes of RB-PDAT against multidrug-resistant P aeruginosa keratitis.

Results

Among the 9 patients included in the analysis (5 women and 4 men; mean [SD] age, 73.4 [14.0] years), all samples tested positive for exoU and carbapenemase-resistant blaVIM and blaGES genes. Additionally, isolates were resistant to carbapenems as indicated by minimum inhibitory concentration testing. In vitro efficacy of RB-PDAT indicated its potential application for treating recalcitrant cases. These cases highlight the rapid progression and challenging management of multidrug-resistant P aeruginosa. Two patients were treated with RB-PDAT as an adjuvant to antibiotic therapy and had improved visual outcomes.

Conclusions and Relevance

This case series highlights the concerning progression in resistance and virulence of P aeruginosa and emphasizes the need to explore alternative therapies like RB-PDAT that have broad coverage and no known antibiotic resistance. The findings support further investigation into the potential effects of RB-PDAT for other multidrug-resistant microbes.

Introduction

Multidrug-resistant Pseudomonas aeruginosa gained notoriety after the Centers for Disease Control and Prevention (CDC) classified the pathogen as a serious threat in 2019.¹ P aeruginosa is a leading cause of bacterial keratitis worldwide.^2,3,4 These opportunistic infections have a variety of intrinsic and extrinsic survival mechanisms that make them challenging to treat and eradicate. Notably, the type III secretion system (T3SS) of P aeruginosa exotoxins exoS, exoT, exoU, and exoY are crucial for understanding pathogenicity.^{5,6,7,8,9,10,11,12} Over the last decades, strains of antibiotic-resistant P aeruginosa have emerged in bacterial keratitis.

P aeruginosa keratitis resistance has been reported against a variety of commonly used cephalosporins, aminoglycosides, and fluroquinolones.¹³ A 10-year retrospective observational case series from Mexico City reported a 5-fold increase of resistance to ceftazidime over the latter 5-year interval compared with the first.¹⁴ Another retrospective study in India examined the outcomes of 15 eyes with extensive and pandrug-resistant (XDR) Pseudomonas keratitis. Only 16% of patients had resolution of their disease following medical treatment alone, and 58% of these patients had poor response to medical therapy.¹⁵ A larger case-control study from L.V. Prasad Eye Institute¹⁶ demonstrated that isolates with multidrug-resistant strains of Pseudomonas keratitis were more likely to cause perforation. Furthermore, fluoroquinolone-resistant exoU-positive and exoS-negative isolates from the Steroids for Corneal Ulcers Trial¹⁷ were associated with increased cytotoxicity and worse clinical outcomes.¹²

In February 2023, the CDC, in collaboration with the US Food and Drug Administration, issued a national alert, warning clinicians of an extensively drug-resistant strain of P aeruginosa (VIM-GES-CRPA).¹⁸ Subsequently, on March 22, 2023, Shoji et al¹⁹ provided detailed observations of a case of severe VIM-GES-CRPA keratitis after use of artificial tears, with cultures of the corneal infiltrate and the patient’s artificial tear drops identifying the same strain of VIM-GES-CPRA. As of now, this carbapenem-resistant strain is linked to 81 cases across 18 states, including Florida (eFigure 1 in Supplement 1); infection has resulted in 4 deaths, permanent vision loss in 14 patients, and enucleation in 4 patients.¹ The most common risk factor in this cluster of cases was the use of contaminated artificial tears.

The emergence of these resistant microorganisms highlights the need for alternative strategies to combat severe corneal infections. One such therapy is rose bengal–photodynamic antimicrobial therapy (RB-PDAT), which uses a diagnostic ophthalmic dye activated with green light to generate antimicrobial oxygen-free radicals that damage the DNA and the cytoplasmic membrane of the bacteria.²⁰ Studies of RB-PDAT have shown in vitro^20,21,22 and in vivo^23,24,25 efficacy against a wide variety of ocular microorganisms.

Between January 1, 2022, and October 31, 2023, 9 cases of VIM-GES-CRPA were confirmed at Bascom Palmer Eye Institute (BPEI) in Miami, Florida. The goal of the present study was to assess the clinical course and outcomes and microbiological diagnostic profiles of VIM-GES-CRPA keratitis and the utility of RB-PDAT as an alternative or adjunctive therapy to treat VIM-GES-CRPA isolates.

Methods

Clinical Observations

This retrospective case series followed the reporting guidelines for uncontrolled case series described by Kempen²⁶ for all patients with a confirmed diagnosis of VIM-GES-CRPA infection at BPEI between January 1, 2022, and October 31, 2023. Institutional review board approval was obtained from the University of Miami Miller School of Medicine Sciences Subcommittee for the Protection of Human Subjects, and informed consent was waived due to the use of retrospective data. The research adhered to the Tenets of the Declaration of Helsinki.²⁷ Patients’ medical records were reviewed and evaluated for sex (which was self-reported), age, and health risk factors, including ocular and medical histories, ophthalmic drop use, contact lens use, exposure to contaminants, and chronic autoimmune diseases. Additionally, other relevant history was observed, including treatment prior to referral and during BPEI admission, time to presentation, initial and last follow-up vision, and other health complications.

Microbiological Profiling

Ocular tissue and fluid samples were collected from patients with presumed ocular infections and plated on a combination of solid (chocolate, 5% sheep blood agar, CDC anaerobic blood agar, sabouraud agar, and liquid media [thioglycollate broth]). Plates and broth were incubated in carbon dioxide (chocolate, blood agars, and thioglycolate) for up to 10 days. Recovered isolates were identified using a combination of Gram stain, oxidase, and conventional biochemicals. Definitive microbial identification and antibiotic-resistant profiles were determined using an automated system (VITEK 2; bioMèrieux). Interpretations of susceptible, intermediate, and/or resistant minimal inhibitory concentrations were in accordance with the Clinical and Laboratory Standards Institute guidelines.²⁸ Carbapenemase resistance was confirmed using gradient diffusion strips (Liofilchem MTS; Fisher Scientific International Inc).

Genomic resistance to carbapenems was determined using standard polymerase chain reaction (PCR) and sequencing to screen for the presence of carbapenemase-encoding resistance genes, including Guiana extended-spectrum β-lactamase (blaGES), imipenemase (bla_IMP), New Delhi metallo β-lactamase (blaNDM), and Verona Integron-mediated metallo-β-lactamase (blaVIM) as described by Monteiro et al.²⁹ Additionally, P aeruginosa T3SS profiles were investigated with a multiplex PCR assay for the 4 effector genes, exoS, exoT, exoU, and exoY, as described by Stepińska and Trafny.³⁰

In Vitro Susceptibility of RB-PDAT

In vitro susceptibility of RB-PDAT was performed as previously described.^23,24,25 Nine genetically confirmed clinical VIM-GES-CRPA isolates from patients were isolated and grown in blood agar plates (A10; Hardy Diagnostics) and placed in an incubator for 48 hours at 3°C. On the day of experiments, strains were suspended in tryptic soy broth (R064890; Remel Products) and prepared into an inoculum of 10 × 10⁸ colony-forming U/mL by matching with a 0.5 McFarland. A solution of 0.1% rose bengal was prepared by dissolving 40 mg of rose bengal (198250; Sigma-Aldrich) in 40 mL of 0.9% sodium chloride solution (Z1377; Cytiva). Nine milliliters of 0.1% rose bengal solution was mixed with 1 mL of inoculum for a final organism concentration of 10 × 10⁴ colony-forming U/mL. Experimental groups were categorized as follows: (1) P aeruginosa only, (2) P aeruginosa with 0.1% rose bengal solution in the dark, and (3) P aeruginosa with 0.1% rose bengal solution with green light. Under minimal light conditions, 1-mL aliquots of the P aeruginosa suspension were plated onto blood agar in triplicate and divided by light condition. Green light irradiation (λ = 518 nm; full-width–half-maximum = 25 nm) was performed with a custom-built 47-mm-diameter LED panel with a peak irradiance of 6-mW/cm² in the center of the irradiation zone measured by a power meter. Plates in the rose bengal–green light group were exposed to 15 minutes of green light irradiation for an energy density of 5.4 J/cm². After irradiation, all plates were immediately placed inside a light-proof container to prevent light activation and stored in an incubator at 37 °C for 48 hours. Then, plates were photographed (D7000; Nikon Inc) to measure bacterial growth inside of the central 47-mm irradiation zone.

Results

Clinical Data

Patient demographic characteristics, presentations, and outcomes for the 9 clinical cases of VIM-GES-CRPA keratitis encountered at BPEI are detailed in Table 1 (5 women and 4 men; mean [SD] age, 73.4 [14.0] years). All patients self-reported as White and 7 as Hispanic. Cases 1 to 8 were reported in February by the CDC,¹⁸ and case 3 was reported by Shoji et al.¹⁹ Data on case 3 have been updated to reflect progression since March 2023, and case 9 has not been reported previously. All patients had compromised ocular surface disease and/or immunosuppression. All patients were prescribed over-the-counter artificial tears to manage ocular surface discomfort, and all self-reported use of EzriCare artificial tears (Global Pharma Ltd). Physical bottles were provided by 3 patients for microbial testing. Treatment with broad-spectrum fortified antibiotics at presentation (vancomycin hydrochloride, 25 mg/mL and tobramycin sulfate, 14 mg/mL) was discontinued once the organism was confirmed as P aeruginosa. The 1% imipenem drops given to patients were compounded in our pharmacy. In the initial cases, we were unaware that the patients shared the same causative organism despite their similar, severe, rapidly progressing ocular infections with scleral and vitreal involvement. On pathogen identification, in vitro susceptibility testing of RB-PDAT was performed and offered to patients without vitreal involvement. The protracted clinical course, final resolution, and photographs (Figure 1 and Figure 2) of the 2 clinical cases treated with RB-PDAT are detailed below.

Table 1. Confirmed VIM-GES-CRPA Keratitis at Bascom Palmer Eye Institute.

Case No.	Age/sex	Risk factors	Previous antibiotics	Time to presentation, d	Antibiotic regimen at BPEI	Intervention at BPEI	Complications	Initial BCVA	Final BCVA
1a	70s/M	AT use, PBK	Bacitracin, moxifloxacin, Muro, prednisolone	4	Moxifloxacin, prednisolone, tobramycin, vancomycin	PKP	NA	LP	HM
2a	90s/F	AT use, HSVK, PBK	Oral acyclovir, ganciclovir, loteprednol	6	Ciprofloxacin, moxifloxacin, prednisolone, tobramycin, vancomycin	PKP	Hemorrhagic CE, RD	20/300	LP
3b	70s/M	CL use, AT use	Vancomycin	1	Imipenem, tobramycin, vancomycin	FALK	NA	HM	20/350
4a	50s/M	Exposure to sewer water, AT use, HSVK, NK	Moxifloxacin, tobramycin	2	Ciprofloxacin, prednisolone, tobramycin	PKP, s/p PPV with intravitreal injections	Endophthalmitis	HM	Counting fingers at 10 m
5a	40s/M	Corneal erosion, AT use, HSVK	NA	Undetermined	Besifloxacin, oral doxycycline, polymyxin B, prednisolone, tobramycin, vancomycin	s/p RB-PDAT, DALK	NA	20/80	20/60
6a	70s/F	AT use, PKP	Moxifloxacin, prednisolone	3	Ciprofloxacin, moxifloxacin, prednisolone, tobramycin, vancomycin	NA	NA	E at 10 m	E at face
7a	70s/F	AT use, failed corneal graft, NK	Erythromycin ointment	1	Ciprofloxacin, moxifloxacin, prednisolone, tobramycin, vancomycin	PKP	Endophthalmitis CP, serous and hemorrhagic CEs, RD 2 mo after TPK	HM	LP
8a	80s/F	AT use, RA, SP	NA	Undetermined	Moxifloxacin, prednisolone	NA	NA	20/150	20/80
9	80s/F	AT use, RA	Prednisolone	Undetermined	Ceftazidime, imipenem, polymyxin B, tobramycin, vancomycin	DBD, patch graft, PPV, RB-PDAT plus AMT (2 sessions)	Endophthalmitis, RD, CD	Counting fingers at face	HM

Abbreviations: AMT, amniotic membrane transplant; AT, artificial tears; BCVA, best-corrected visual acuity; BPEI, Bascom Palmer Eye Institute; CD, choroidal detachment; CE, choroidal effusion; CL, contact lens; CP, corneal perforation; DALK, deep anterior lamellar keratoplasty; DBD, corneal epithelial debridement; FALK, femtosecond anterior lamellar keratoplasty; HM, hand motion; HSVK, herpes simplex virus keratitis; LP, light perception; NA, not available; NK, neurotrophic keratitis; PBK, pseudophakic bullous keratoplasty; PKP, penetrating keratoplasty; PPV, pars plana vitrectomy; RA, rheumatoid arthritis; RB-PDAT, rose bengal–photodynamic antimicrobial therapy; RD, retinal detachment; s/p, status post; SP, scleromalecia perforans; TPK, total penetrating keratoplasty; VIM-GES-CRPA, multidrug-resistant Pseudomonas aeruginosa.

^a Reported in the February 2023 Centers for Disease Control and Prevention (CDC) report.¹⁸

^b Reported in the February 2023 CDC report¹⁸ and by Shoji et al.¹⁹

Figure 1. Progression of Case 5.

The patient presented with severe pain and decreased vision of his left eye. On day 7, a 6.5 × 6.8-mm epithelial defect with underlying infiltrate and 2.4-mm hypopyon was noted and was unchanged on day 10. The patient received rose bengal–photodynamic antimicrobial therapy for multidrug-resistant Pseudomonas aeruginosa keratitis, with improvement noted on days 12 and 17. Treatment with prednisolone drops followed with tapering through day 90. At day 180, best-corrected visual acuity was 20/800 and examination revealed a central corneal scar.

Figure 2. Progression of Case 9.

The patient presented with worsening redness and visual loss in her right eye and a large peripheral ulcer at the nasal limbus. On day 3, nasal cornea demonstrated significant thinning, and B-scan ultrasonography revealed vitreous opacities. On day 7, visual acuity worsened to light perception, and the patient underwent a patch graft with placement of an amniotic membrane transplant and conjunctiva flap on day 8. The patient received rose bengal–photodynamic antimicrobial therapy (RB-PDAT) for multidrug-resistant Pseudomonas aeruginosa keratitis, and the infiltrate slowly resolved (day 22). On day 30, recurrent infiltrate developed, and corneal melt subsequently developed (day 40). Additional RB-PDAT was administered with repeat amniotic membrane transplant and corneal debridement. At day 60, the infiltrate was largely resolved and the graft was epithelializing.

Case 5

A man in his 40s with a history of herpes simplex virus keratitis and recurrent corneal erosion presented to our emergency department with severe pain and decreased vision in his left eye. He reported use of artificial tears for 5 months prior to presentation. His initial best-corrected visual acuity (BCVA) was 20/80 measured and his initial examination results revealed an inferior 4.5 × 3.5-mm corneal epithelial defect with underlying infiltrate. Corneal cultures were collected, and treatment with fortified vancomycin hydrochloride (25 mg/mL) and tobramycin sulfate (14 mg/mL) drops every hour while awake was started.

One week later, the patient presented with light perception visual acuity. On examination, a 6.5 × 6.8-mm epithelial defect with underlying infiltrate and 2.4-mm hypopyon was noted (Figure 1A). B-scan ultrasonography did not reveal any evidence of vitritis. Corneal cultures yielded an XDR strain of P aeruginosa. Treatment with vancomycin and tobramycin drops was stopped and replaced with polymyxin B sulfate drops every hour while awake and oral doxycycline, 50 mg twice a day. On day 10 of treatment, his visual examination results were grossly unchanged (Figure 1B); his BCVA remained at light perception and his B-scan ultrasonogram was unrevealing.

The patient at this time agreed to proceed with RB-PDAT. Clinical improvement was observed 2 and 7 days after RB-PDAT, with a decrease in the size of his infiltrate (Figure 1C) and hypopyon (Figure 1D). He continued treatment with topical polymyxin B for 2.5 months after RB-PDAT (Figure 1E); treatment with prednisolone drops was started 1 week after RB-PDAT and continued for 4 months with slow tapering. Six months after RB-PDAT, his BCVA was 20/800, and his examination revealed a central corneal scar (Figure 1F). Seven months after RB-PDAT, a partial corneal transplant was performed. Six months after corneal transplant, BCVA improved to 20/60.

Case 9

A woman in her 80s with a history of rheumatoid arthritis and systemic lupus erythematosus presented at BPEI for 3 months of worsening redness and visual loss in her right eye. She was previously treated with an unknown topical antibiotic drop. On presentation, the visual examination revealed a large peripheral ulcer at the nasal limbus. Corneal cultures were collected on presentation, and treatment with fortified tobramycin and vancomycin antibiotics was started.

Three days after presentation (Figure 2A), her nasal cornea demonstrated significant thinning, and B-scan ultrasonography revealed vitreous opacities causing concern for endophthalmitis. The patient underwent a vitreous tap and injection of intravitreal ceftazidime. Cyanoacrylate glue was placed in the area of corneal thinning. The vitreous cultures yielded no growth, but the corneal cultures ultimately yielded P aeruginosa resistant to all antibiotics except meropenem. Treatment was then switched to 1% imipenem drops and topical tobramycin every hour while awake and oral ciprofloxacin, oral doxycycline, and topical prednisolone drops 4 times a day.

On day 7 of treatment (Figure 2B), the patient’s BCVA worsened to light perception; results of a Seidel test were positive, and B-scan ultrasonography revealed shallow choroidal detachments and a retinal detachment. The patient was then taken to the operating room on day 8 of treatment for a patch graft with placement of an amniotic membrane transplant and conjunctiva flap in addition to intracameral imipenem and RB-PDAT. Two weeks after the procedure, treatment with imipenem drops was tapered and her infiltrate slowly resolved over the following weeks (Figure 2C).

After the procedure, the patient revealed using artificial tears prior to her symptom onset for several months. She was able to bring a tear bottle to our clinic, which was cultured and yielded XDR P aeruginosa with partial sensitivity to polymyxin B only. The patient started treatment with polymyxin B, contributing to a mild improvement in her condition following the patch graft. However, 3 weeks following surgery (Figure 2D), she developed a recurrent infiltrate that subsequently developed into a corneal melt (Figure 2E). The patient underwent corneal debridement, repeat placement of layered amniotic membrane transplant, and RB-PDAT treatment. She continued to have persistent choroidal detachments on B-scan ultrasonography (although with resolution of her prior retinal detachment). Her BCVA fluctuated between hand motion and light perception.

Due to her severe disease course, the patient was offered enucleation, which she refused. After her second procedure, the patient’s condition slowly began to improve. One month after her second operation, her infiltrate was largely resolved, and her patch graft was epithelializing well (Figure 2F). She continued treatment with topical moxifloxacin and prednisolone in addition to serum tears and aggressive lubrication. At her last follow-up examination, her final BCVA was documented at hand motion, and her final B-scan ultrasonogram also showed resolution of the choroidal detachments.

Microbiological Diagnostic Profiling

A total of 23 VIM-GES CRPA isolates (68%) were recovered from 33 submitted ocular samples (Table 2). At least 1 isolate was recovered from each of the 9 patients. The number of submitted ocular samples per patient ranged from 1 to 8, with a mean (SD) of 3.8 (2.3).

Table 2. Source Distribution of Recovered VIM-GES-CRPA Isolates at BPEI Between January 1, 2022, and October 31, 2023.

Source	No. of samples	VIM-GES-CRPA positive, No. (%)
Anterior chamber fluid	2	2 (100)
Bandage contact lens	1	1 (100)
Conjunctiva	1	1 (100)
Cornea scrapings	13	11 (85)
Cornea button	2	2 (100)
Intraocular lens	2	0
Pupillary membrane	2	1 (50)
Retrocorneal membrane	2	0
Sclera	1	1 (100)
Vitreous chamber fluid	1	0
Artificial tears	6	4 (67)
All	33	23 (70)

Abbreviations: BPEI, Bascom Palmer Eye Institute; VIM-GES-CRPA, multidrug-resistant Pseudomonas aeruginosa.

All isolates were identified as P aeruginosa by the VITEK 2 system with a biochemical fingerprint match greater than 95%. Genomic sequencing also identified the isolates as P aeruginosa with a similarity of at least 99%. The resistotype included resistance to aminoglycosides, cephalosporins, fluoroquinolones, and carbapenems (Table 3). Additionally, multiplex PCR revealed that the multidrug genomic resistance was mediated by a unique combination of carbapenemase-resistance genes blaVIM80 (NG_079261.1) and blaGES9 (AY920928.1). Both resistance genes were found in all isolates. All strains were classified as cytotoxic because they were positive for exoU secretion (exoU positive and exoS negative).

Table 3. Susceptibility Profiles of VIM-GES-CRPA Isolates at BPEI.

Case No.	Amikacin		Cefepime		Ceftazidime		Ciprofloxacin		Gentamycin		Levofloxacin		Meropenem		Tobramycin
	MIC, μg/mL	SC	MIC, μg/mL	SC	MIC, μg/mL	SC	MIC, μg/mL	SC	MIC, μg/mL	SC	MIC, μg/mL	SC	MIC, μg/mL	SC	MIC, μg/mL	SC
1	≥64	R	≥64	R	≥64	R	≥4	R	≥16	R	≥8	R	4	I	≥16	R
2	≥64	R	≥64	R	≥64	R	≥4	R	≥16	R	≥8	R	8	R	≥16	R
3	≥64	R	≥64	R	≥64	R	≥4	R	≥16	R	≥8	R	4	I	≥16	R
4	≥64	R	≥64	R	≥64	R	≥4	R	≥16	R	≥8	R	8	R	≥16	R
5	≥64	R	≥64	R	≥64	R	≥4	R	≥16	R	≥8	R	4	I	≥16	R
6	≥64	R	≥64	R	≥64	R	≥4	R	≥16	R	≥8	R	8	R	≥16	R
7	≥64	R	≥64	R	≥64	R	≥4	R	≥16	R	≥8	R	4	I	≥16	R
8	≥64	R	≥64	R	≥64	R	≥4	R	≥16	R	≥8	R	4	I	≥16	R
9	≥64	R	≥64	R	≥64	R	≥4	R	≥16	R	≥8	R	4	I	≥16	R

Abbreviations: BPEI, Bascom Palmer Eye Institute; I, intermediate; MIC, minimum inhibitory concentration; R, resistant; SC, susceptibility profile interpretation; VIM-GES-CRPA, multidrug-resistant Pseudomonas aeruginosa.

Rose Bengal Photodynamic Antimicrobial Therapy

Rose bengal–PDAT without green light had no impact on the growth of VIM-GES-CRPA when compared with the control group 48 hours after incubation (eFigure 2 in Supplement 1). Rose bengal–PDAT fully inhibited all VIM-GES-CRPA inside of the central 47-mm irradiation zone. Observed P aeruginosa in vitro susceptibility provided reason to potentially treat patients with RB-PDAT.

Discussion

This case series adds to previous publications^19,31,32 of patients associated with a recent artificial tear contamination outbreak. The aggressive, protracted management and worse outcomes associated with these unique strains of extensive-resistance P aeruginosa are highlighted in our 7-month experience. Five of the patients in this series were treated at BPEI prior to the CDC and US Food and Drug Administration alert of VIM-GES-CRPA–tainted artificial tears.

All of our cases were related to use of EzriCare artificial tears, and 3 EzriCare bottles were brought in for culture that yielded XDR isolates (excluding partial polymyxin B sensitivity in case 9). Various incidents of contaminated ocular medications predate the 2023 artificial tear recall, including the 2005 Fusarium keratitis-linked Bausch & Lomb recall of contact lens disinfectant and the 2007 Acanthamoeba keratitis–linked Advanced Medical Optics recall of contact lens solution.^33,34

In cases 5 and 9 of the present study, RB-PDAT was implemented and stabilized ocular surface for additional vision salvage procedures. The visual outcome in case 5 was 20/800 due to corneal scarring, but the patient underwent deep anterior lamellar keratoplasty, and the final visual outcome was 20/60. In case 9, RB-PDAT retreatment was needed after the patient’s recurrent infiltrate led to corneal melt and severe necrotizing scleritis. The patient’s infiltrate demonstrated improvement after repeat RB-PDAT. Her corneal patch graft fully epithelized and the scleral necrosis resolved.

Three patients with VIM-GES-CRPA infection (33%) experienced progression to endophthalmitis following treatment initiation with topical antimicrobials. The disease progression to endophthalmitis is rare.³⁵ Of note, patients 4 and 7 had histories of keratitis and patient 9 had a history of rheumatoid arthritis, both well-documented risk factors for recurrent destructive corneal disease.^36,37 Five cases (56%) precipitated intervention with penetrating keratoplasty after refractory topical broad-spectrum treatment.

Overall, the combination of multidrug resistance and T3SS profile was unique in these cases. The consequences of T3SS effector distribution in P aeruginosa keratitis can influence treatment strategies and outcomes. Pathology was enhanced by resistance to commonly used ocular drugs and the aggressive tissue destruction associated with exoU- and exoS-positive strains.

The pathogenicity of P aeruginosa is postulated to result from multiple secreted virulence factors as well as intrinsic and extrinsic mechanisms of antibiotic resistance.^7,8 The most extensively studied secretion system is the contact-dependent T3SS,⁶ a requisite for P aeruginosa to survive in corneal epithelial cells.^9,10,38 Most strains encode for both exoT and exoY but are mutually exclusive for exoS and exoU¹⁵; exoS attributes to P aureginosa’s invasive activity, while exoU attributes to their cytotoxic capacity,^11,39,40,41 and both phenotypes activate apoptotic signaling.^42,43,44 Multiplex PCR of our corneal isolates revealed that all were cytotoxic strains (exoU positive and exoS negative), coinciding with the 2018 University of South Wales microbial keratitis study, which showed that 62% of isolates possessed the exoU gene, with 12 of 13 resistant to 3 or more β-lactams.⁴⁵ Another collection of T3SS keratitis isolates favored epidemic clones of genes encoding exoU when compared with control patients.⁴⁶

The concerning progression in resistance and virulence of P aeruginosa highlights the need to explore alternative therapeutics, including new antibiotics, phage therapy, monoclonal antibodies,⁴⁷ and photodynamic therapy. Only cefiderocol, a last-resort siderophore cephalosporin, is indicated in in vitro susceptibility to these XDR isolates, but its use is limited as there is no current ocular preparation.⁴⁸ Phage therapy has proven effective against the management of P aeruginosa keratitis,^49,50,51 yet its use is strain specific. Additionally, development of antiseptics and antimicrobial peptides are warranted for these recalcitrant pathogens.⁵²

Rose bengal–PDAT is a novel procedure proposed for the management of resistant microbial infectious keratitis, including methicillin-resistant Staphylococcus aureus.²² The potential advantage of RB-PDAT as a treatment is due to the generation of singlet oxygen, which causes cross-linking of the collagen fibers and an antimicrobial effect.^23,24,53 Cross-linking could be potentially useful in treating Pseudomonas infections since it increases the tensile strength of the cornea and prevents the bacterium from causing severe corneal ulceration.²⁴ Additionally, PDAT is a broad-spectrum therapeutic and has no known microbial resistance in vitro.²⁰ Our small case series, which used a retrospective design without controls, provides evidence but cannot provide definite support of the potential use of RB-PDAT in similar cases of resistant microbial strains to preserve visual outcomes.

Limitations

This study has some limitations. Our study was limited by its small, retrospective cohort without any controls. Additionally, our cases had variable presentations and different follow-up durations.

Conclusion

This case series of exoU-positive VIM-GES-CRPA corneal isolates calls attention to the importance of culture- and genetics-based methods of pathogen identification whenever possible. The pathogenic and antimicrobial-resistant cultures of artificial tears preceding keratitis infection emphasize the importance of screening patients for past or current artificial tear use. The use of RB-PDAT adjunct therapy in this subset of patients without intraocular involvement may improve ocular integrity and visual outcomes.

Supplement 1.

eFigure 1. Geographical Distribution of VIM-GES-CRPA in the US

eFigure 2. Multidrug-Resistant Pseudomonas aeruginosa After 48 Hours of Incubation

Supplement 2.

Data Sharing Statement