Antibiotic Resistance Trends Among Ocular Pathogens in the US—Cumulative Results from the Antibiotic Resistance Monitoring in Ocular Microorganisms (ARMOR) Surveillance Study

US Ophthalmic Review, 2017;10(1):35–8 DOI:


Antibiotic resistance among ocular pathogens is a public health concern. The multicenter, prospective Antibiotic Resistance Monitoring in Ocular micRoorganisms (ARMOR) study is an ongoing surveillance study designed to report on antibiotic resistance rates and trends among Staphylococcus aureus, coagulase-negative staphylococci (CoNS; includes Staphylococcus epidermidis), Streptococcus pneumoniae, Pseudomonas aeruginosa, and Haemophilus influenzae isolates from ocular infections. Results for more than 4,000 isolates collected from 2009 –2015, representing 7 years of ARMOR, were recently presented. More than a third of S. aureus and almost half of all CoNS isolates were found to be resistant to methicillin. Staphylococcal isolates also showed high levels of multidrug resistance (resistance to ≥3 antibacterial drug classes) with 76.4% and 73.7% of methicillin-resistant S. aureus (MRSA) and methicillin-resistant CoNS (MRCoNS) isolates, respectively, demonstrating multidrug resistance. Resistance among S. pneumoniae was notable for azithromycin (36.8%) and for penicillin (34.0%), whereas P. aeruginosa and H. influenzae were generally susceptible to the antibiotic classes tested. Longitudinal analyses demonstrated a small decrease in methicillin resistance among S. aureus over the 7-year study period, which may be a result of improved antibiotic stewardship. Continued surveillance of antibiotic resistance among ocular pathogens is warranted.
Keywords: ARMOR, surveillance study, antibiotic resistance, ocular infections, Staphylococcus aureus
Disclosure: Penny A Asbell is a consultant to Perrigo and Kurobe, and participates in advisory boards for Valeant/Bausch + Lomb. She is a speaker on continuing medical education topics at professional meetings for Vindico. Christine M Sanfilippo is an employee of Bausch + Lomb.
Acknowledgments: Medical writing assistance was provided by Katrina Mountfort and Michelle Dalton for Touch Medical Media, supported by Bausch + Lomb, a division of Valeant Pharmaceuticals International Inc.

Authorship: All named authors meet the International Committee of Medical Journal Editors (ICMJE) criteria for authorship of this manuscript, take responsibility for the integrity of the work as a whole, and have given final approval to the version to be published.

Open Access: This article is published under the Creative Commons Attribution Noncommercial License, which permits any noncommercial use, distribution, adaptation, and reproduction provided the original author(s) and source are given appropriate credit.
Received: February 16, 2017 Accepted March 09, 2017
Correspondence: Penny A Asbell, MD, MBA, Cornea Service and Refractive Surgery Center, Icahn School of Medicine at Mount Sinai, 1190 Fifth Avenue, Annenberg Bldg 22-12, New York, NY 10029, US. E:
Support: The publication of this article was supported by Bausch + Lomb, a division of Valeant Pharmaceuticals International Inc., who were given the opportunity to review the article for scientific accuracy before submission. Any resulting changes were made at the author’s discretion.

Antibiotic-resistant bacteria cause infections worldwide, with potentially serious health consequences,1 although the majority of such infections involve resistance to systemically administered antibiotics used in the treatment of systemic infections. The first case of methicillin resistance in Staphylococcus aureus (MRSA) was reported in 1961, and was an uncommon finding until the 1990s when community-acquired MRSA became so prevalent in the general population that health authorities considered it endemic.2 Although the incidence of healthcare-associated MRSA infections is declining due to preventive hygiene measures in the hospital setting, rates of community-acquired MRSA infections have increased in the general population over the last 10 years. Other pathogens that are resistant to antibiotics include vancomycin-resistant enterococci and multidrug-resistant Streptococcus pneumoniae, Mycobacterium tuberculosis, and Neisseria gonorrhoeae. In the US, the Centers for Disease Control and Prevention (CDC) and leading scientists have developed strategies to help reduce antibiotic resistance that include improving diagnosis, tracking and prescribing practices, optimizing therapeutic regimens, adopting antibiotic stewardship programs, and preventing infection transmission.1

Ophthalmic bacterial infections are often treated before the causative pathogen is identified, and as such, antibiotic resistance in ocular infections is of particular concern. Whether an infection is on the ocular surface or intraocular, permanent loss of vision may result if appropriate treatment is not initiated promptly, and antibiotic-resistant pathogens can complicate treatment selection. S. aureus, coagulase-negative staphylococcal (CoNS), S. pneumoniae, Pseudomonas aeruginosa, and Haemophilus influenzae are common causes of ocular bacterial infections, with both S. aureus and CoNS frequently isolated from conjunctivitis, keratitis, endophthalmitis, and blepharitis.3

There has been a dramatic rise in the prevalence of methicillin-resistant staphylococci in ophthalmic infections. A study of S. aureus isolates from eye infections submitted to The Surveillance Network by more than 200 laboratories in the US from January 2000 to December 2005 showed that the proportion of MRSA increased from 29.5% in 2000 to 41.6% in 2005.4 Microbial keratitis is recognized as a significant sight-threatening complication that may result from refractive surgery with a reported incidence ranging from 0% to 1.5%.5,6 Solomon et al. reported an incidence of one infection for every 2,131 refractive surgery procedures in 2004, which increased to an incidence of one infection every 1,102 procedures in 2011; MRSA was the most common organism cultured.5 High levels of methicillin resistance were also reported for S. aureus (51.9%) and S. epidermidis (56.0%) isolates collected from ocular infections between 2003 and 2008 at the Bascom Palmer Eye Institute.7 In another study, Gentile et al. reported increasing methicillin resistance among staphylococci in their retrospective study of endophthalmitis cases from 1987 to 2011. Methicillin resistance increased from 18% for S. aureus and 31% for Staphylococcus epidermidis in 1987 to 55% for both in 2011.8 MRSA infection and other multidrug-resistant bacterial pathogens can be detrimental to vision and represent a major therapeutic challenge.3,9

There is a paucity of studies that monitor antibiotic resistance among ocular bacteria, and this represents a substantial unmet need. This article aims to describe ocular antibiotic resistance surveillance programs in the US, and to present the latest findings of the Antibiotic Resistance Monitoring in Ocular micRoorganisms (ARMOR) study, the only nationwide ongoing surveillance study specific to ocular bacterial pathogens.

Ocular TRUST
In the past decade, surveillance data have provided clinicians with a large, nationwide picture of resistance and susceptibility patterns in ocular infections. The Tracking Resistance in the United States Today (TRUST) study was developed with the objective of evaluating in vitro susceptibility of bacterial isolates collected yearly from approximately 200 clinical laboratories throughout the US.10 At the time of inception, ocular isolates were not a primary consideration although ocular isolates were periodically submitted.

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Keywords: ARMOR, surveillance study, antibiotic resistance, ocular infections, Staphylococcus aureus