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Focus On Antibiotic Resistance | Feb 2015

Sidebar: From TRUST to ARMOR: Where We Stand

The Centers for Disease Control and Prevention (CDC) reports that approximately 2 million Americans experience an infection with an antibiotic-resistant microorganism each year.1 Antibiotic-resistant infection can occur in any part of the body, and the eyes are no exception. Drug-resistant ocular infections, once a rarity, have become much more common.

The CDC has developed a program to try to gain an upper hand in the battle against these growing enemies in our midst, the multidrug-resistant microorganisms called superbugs. The CDC identified four core actions to serve as a long-term solution to this preeminent problem.1 These core actions are described as follows:

  • detecting and tracking patterns of antibiotic resistance
  • responding to outbreaks involving antibiotic-resistant bacteria;
  • preventing infection from occurring and bacterial resistance from spreading
  • discovering new antibiotics and new diagnostic tests for resistant bacteria.

Tracking antibiotic resistance—one of the four core actions of the CDC—is not a new endeavor. One of the most effective surveillance strategies for antibiotic-resistant ocular infection is the ARMOR study. This ongoing effort strives to be more than just intellectual armor against the epidemic of antibiotic resistance; it also actively tries to combat the spread of these agents.

A predecessor of ARMOR was the Ocular TRUST study. This surveillance study looked closely at the prevalence of ocular antibiotic resistance and monitored the susceptibility patterns of ocular isolates between the years 2000 and 2005, and again from 2005 to 2006.2 The ARMOR surveillance program was designed and implemented in 2009 in the United States to continue the efforts of the Ocular TRUST program.

Findings from the ARMOR study were first published in 2011, documenting the results of cultures of ocular isolates obtained in 2009.3 This study has continued every year, and the most recent ARMOR study contained data from isolates collected in 2012 and 2013.4 In 2012, the ARMOR surveillance study includeds sites in Canada as well.


Ocular antibiotic resistance was once a rare condition. Over years of repeated use of ophthalmic antibiotics, bacteria have become more resilient and harder to kill. The CDC's core actions were designed to provide effective means to fight the epidemic of antibiotic resistance.

Tracking the changes in microbial culture results and the susceptibility profile patterns of ocular antibiotics over time can help to determine which types of ophthalmic antibiotics are most effective against specific types of bacteria or other pathogenic microorganisms. Surveillance studies such as ARMOR can also help guide eye care professionals to prevent the abuse and misuse of ocular antibiotics and keep them from being rendered ineffective by resistant microorganisms.

This monitoring strategy can also lead to effective implementation of other CDC core actions, such as preventing the spread of antibiotic resistance. Tracking changes over time can also help to determine whether certain antibiotics need to be “rested,” which antibiotics should continue to be actively used, and the rate at which any one species of bacteria may be on the run towards antibiotic resistance.

In 2012, the ARMOR study included 798 ocular infection isolates from 32 sites in the United States. This study included 289 isolates of Staphylococcus aureus, 268 isolates of coagulase-negative staphylococci, 82 isolates of Streptococcus pneumoniae, 73 isolates of Haemophilus influenzae, and 86 isolates of Pseudomonas aeruginosa; to date in 2013, 239 isolates from 27 sites were collected.4

It is important to note that results have changed substantially over time, and the ARMOR study has documented this. In the initial study from 2009, large percentages of S aureus and coagulase-negative staphylococci were found to be resistant to oxacillin, methicillin, azithromycin, or fluoroquinolones. Furthermore, 46.5% of isolates with S aureus, 58.3% of isolates with coagulase negative staphylococci, 9.0% of isolates with P aeruginosa, and 9.3% of pneumococcal isolates were nonsusceptible or resistant to two or more antibiotic drug classes. Only 2.7% of H influenzae isolates were resistant to one of the antimicrobial agents tested.

In the most recent studies of 2012 and 2013, the ARMOR data showed that S aureus and coagulase-negative staphylococci species continued to demonstrate high rates of resistance to a number of antibiotics. Specifically, both microorganisms had resistance rates exceeding 25% for eight of the 15 representative antibiotics tested. Preliminary ARMOR 2013 results indicate that S aureus and coagulase-negative staphylococci were non-susceptible to oxacillin (43%-59%), ciprofloxacin (33%-43%), clindamycin (21%), and azithromycin (60%-63%), showing slight increases over the previous year. Very important and worth noting is that multidrug resistance to three or more classes of antibiotics also remained prevalent in S aureus and coagulase-negative staphylococci isolates (38%-39%), especially among methicillin-resistant staphylococci (60%-81%).


To summarize the data collected over the years of the ARMOR surveillance study, it has been noted that the antibiotic resistance of pathogenic bacteria identified in these studies has gradually increased over the course of time. In addition, these same ocular bacteria have developed resistance to more classes of antibiotics each year, and the rates of resistance to these specific drug classes have also increased as well.

The rise of bacterial resistance is quickly becoming a major concern in ophthalmology clinics. With increases in the frequency of ophthalmic surgical procedures due to the aging of the population, the fight against these pathogens in the prevention of infections and complications will be a continued challenge. With few products in the pipeline to take over for older antimicrobials, the processes of monitoring antimicrobial resistance and carefully husbanding the use of existing molecules will be important in our clinical decision-making processes in the management of ocular infections.n

1. Detect and Protect Against Antibiotic Resistance. Centers for Disease Control and Prevention website. http://www.cdc.gov/drugresistance/detect-and-protect/. Accessed January 14, 2015.

2. Asbell PA, Colby KA, Deng S, et al. Ocular TRUST: nationwide antimicrobial susceptibility patterns in ocular isolates. Am J Ophthalmol. 2008;145(6):951-958.

3. Haas W, Pillar CM, Torres M, et al. Monitoring antibiotic resistance in ocular microorganisms: results from the Antibiotic Resistance Monitoring in Ocular micRorganisms (ARMOR) 2009 surveillance study. Am J Ophthalmol. 2011. 201;152(4):567-574.

4. Sanfilippo CM, Morris TW, Deane J, et al. Antibiotic resistance profile. Poster presented at: The Association for Research in Vision and Ophthalmology (ARVO) 2014; May 4-8, 2014; Orlando, FL.

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