New research from the Antibiotic Resistance Monitoring in Ocular micRoorganism (ARMOR) study is offering updated findings on antibiotic resistance among intraocular isolates.
Released during the 2023 American Academy of Ophthalmology (AAO) annual meeting, the findings were presented by study author Penny Asbell, MD, FACS, MBA, FARVO, professor in the Department of Bioengineering at the University of Memphis in Memphis, Tennessee.
Dr. Asbell spoke with Glance regarding the new data.
So… why antibiotic resistance?
Antibiotic resistance is a global problem, Dr. Asbell said. “What we don’t realize is that it's a problem for eye diseases as well.”
Despite a decrease in resistance—specifically methicillin—in the last 15 years, she said, there are still significant concerns.
Case in point: the January 2023 CDC recall of artificial tears due to Verona Integron‐mediated Metallo‐β‐lactamase (VIM)‐ and Guiana‐Extended Spectrum‐β‐Lactamase (GES)‐ producing carbapenem‐resistant Pseudomonas aeruginosa (VIM-GES-CRPA) eye infections (see the coverage here, here, and here) and, just last week, the FDA’s warning against 27 eye drops with the potential for eye infections.
And further: endophthalmitis—a rare but serious complication due to ocular surgery and intraocular injections often caused by a patient’s own bacterial flora.
Now this ARMOR study: what is it?
Launched in 2009 and funded by Bausch + Lomb, the ARMOR study is the only ongoing nationwide antibiotic resistance surveillance program focusing specifically on ocular pathogens.
The goal: to observe and report resistance rates and trends among common ocular isolates (see below) collected from 88 clinical sites in 41 states:
- Staphylococcus aureus
- Coagulase-negative staphylococci (CoNS)
- Streptococcus pneumoniae
- Haemophilus influenzae
- Pseudomonas aeruginosa
And the findings so far?
Two sets of findings have been published in JAMA Ophthalmology, identifying high rates of methicillin-resistant isolates and high multi-drug resistance (MDR) among methicillin-resistant (MR) isolates:
- 5-year data (2009 - 2013), published in December 2015
- See here for details.
- 10-year data (2009 - 2018), published in April 2020
- See here for details.
Gotcha. So talk about this new data.
Per Dr. Asbell, investigators collected 370 endophthalmitis (vitreous and aqueous humor) isolates of the five common ocular pathogens (listed above) from 44 clinical sites in 22 states between 2009 and 2022, all of which were suspected to be serious eye infections.
They were then tested against common antibiotics.
Which were…?
- Azithromycin
- Chloramphenicol
- Ciprofloxacin
- Clindamycin
- Oxacillin
- Tetracycline
- Tobramycin
- Trimethoprim
- Vancomycin
What’d they find?
Among the isolates, 45% of Staphylococcus aureus and 41% of CoNS were found to be MR—meaning they could be much harder to treat effectively with the typical antibiotics used for eye diseases, she said.
Additionally, 40% of CoNS and 41% of S. aureus were found to have MDR.
According to Dr. Asbell: “S. aureus has high resistance and could very likely be MR, which is also a red flag for being multi-drug resistant.” She also called attention to CoNS, which possesses fewer virulent properties compared to S. aureus.
What risk does CoNS pose?
She referenced recent research published in October 2023 assessing current antibiotic approaches to minimizing the risk of endophthalmitis after cataract surgery
Of importance: the study identified CoNS as the most common bacteria to cause post-op endophthalmitis.
Talk about the other isolates’ antibiotic resistance.
A total of 70% of MRCoNS and 85% of MRSA were found to be resistant to certain antibiotics—ciprofloxacin and azithromycin. S. pneumoniae had a resistance of 39% each for azithromycin and penicillin.
To note, little to no resistance was observed among P. aeruginosa and H. influenzae.
And overall?
Per Dr. Asbell’s poster findings, in vitro antibiotic resistance was observed to be common among the endophthalmitis isolates. This suggests such data may be used to determine antibiotic selection for infection prophylaxis and/or intraocular infections.
Any limitations to consider?
Yup. Four areas were noted:
- Use of systemic breakpoints to interpret minimal inhibitory concentration (MIC)
- To note, MICs are used to determine if a concentration level could kill 90% of the isolates that are tested.
- Diagnosis information was not collected.
- Data was unable to evaluate species prevalence for bacterial endophthalmitis.
- Unclear clinical relevance without consideration given to the tested antibiotics’ ocular pharmacokinetics.
So how can these findings help clinicians?
According to Dr. Asbell, the ARMOR study’s data can be used to determine where to start in selecting an antibiotic.
She referenced a 2018 JAMA study that called for four key questions to consider when beginning the process: 1. Are antibiotics required?
2. Have I ordered the appropriate diagnostic test(s)?
3. Follow up: Is it possible to narrow or change the treatment?
4. What’s the best duration of treatment to mitigate the infection?
And advice to consider?
Taking the study’s data into consideration, Dr. Asbell advised, “When treatment can’t wait, think about ARMOR,” she said. “It can help a clinician make decisions on how to get started; although, ultimately the culture samples and patient response will determine next steps in treatment.”
Dr. Asbell has no financial interest in this study.
The American Academy of Ophthalmology annual meeting is being held Nov. 3-6 2023, in San Francisco, California.