Antibiotic resistance levels shift among ocular pathogens in 2014 ARMOR data

Take-home message: New surveillance data on antibiotic resistance among ocular pathogens shows worrisome trends for some widely used drugs while resistance rates for some isolates were relatively stable.

By Nancy Groves; Reviewed by Penny A. Asbell, MD

New York-An ongoing surveillance study of pathogenic ocular bacteria show high levels of resistance to commonly used antibiotics.

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The Antibiotic Resistance Monitoring in Ocular micRoorganisms (ARMOR) study data indicate that about 1 in 2 Streptococcus pneumoniae isolates were resistant to penicillin, whereas 2 in 5 were resistant to azithromycin.

Methicillin resistance remained high in Staphylococcus aureus (1 in 4). The rate was 1 in 2 among coagulase-negative staphylococci (CoNS).

Dr. Asbell“Methicillin-resistant organisms continue to be fairly commonly found in ocular isolates, whether it’s S. aureus or CoNS,” said Penny A. Asbell, MD, professor of ophthalmology, Icahn School of Medicine at Mount Sinai, New York.

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“Equally important, when resistance is found, most of those organisms are multidrug-resistant,” Dr. Asbell said. “You can’t just change from one group to another and hope you catch it. Those organisms develop mechanisms to become resistant to many of the antibiotics that we typically use.”

However, on a positive note, vancomycin continued to be effective when other antibiotics were not, Dr. Asbell added.

She reported comparisons of susceptibility rates based on 2013 data on 496 bacterial isolates collected from 22 participating sites and preliminary 2014 data on 141 isolates collected from 7 sites.

This is the sixth consecutive year that data from ARMOR, a national survey of resistance levels among ocular pathogens, has been released. Isolates of S. pneumoniae, S. aureus, CoNS, Pseudomonas aeruginosa, and Haemophilus influenzae were tested.

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“What we discovered is that some things are continuing to be issues and that some things appear to be changing a little bit,” Dr. Asbell said. “There continues to be resistance. Specifically, S. pneumoniae continues to be resistant to penicillin.”

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When preliminary data from 2014 were compared with those from 2013, non-susceptibility rates for S. pneumoniae more than doubled for penicillin (22% versus 53%), azithromycin (30% versus 63%), and chloramphenicol (2% versus 11%).

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Resistance to tobramycin among CoNS increased to 35% from 2013 to 2014. CONS non-susceptibility rates to other antibiotics remained relatively steady, although remaining high for azithromycin (65%) and oxacillin (62.5%).

The level of multidrug resistance (defined as resistance to three or more drug classes) decreased in 2014 among S. aureus to 16% and among methicillin-resistant S. aureus to 50%. However, multidrug resistance rates increased to 55% in CoNS and to 84% in methicillin-resistant CoNS.

All the 2014 isolates of H. influenzae were susceptible to the antibiotics tested with the exception of one fluoroquinolone-resistant isolate and one azithromycin-resistant isolate, a piece of good news from the study, Dr. Asbell noted.

In addition, preliminary 2014 data showed decreases from the previous year in the rates of non-susceptibility in isolates of S. aureus to oxacillin, ciprofloxacin, and azithromycin. The resistance rates were 28%, 22%, and 53%, respectively.

Isolates of P.aeruginosa were nonsusceptible to polymyxin B (27%), imipenem (16%), and ciprofloxacin (9%) in 2013, while no resistance was found in the 2014 preliminary dataset. Because the 2014 isolates sample size was smaller than that of previous years, these findings need to be confirmed in the final 2014 dataset.

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“Everybody worldwide is concerned about antibiotic use, increasing resistance, and what’s going to happen in terms of caring for patients appropriately as we get more resistance, and whether antibiotics that we thought would be terrific turn out to be less effective than we expected,” Dr. Asbell said.

“People need to realize that even our fluoroquinolones, which we call broad-spectrum, are not going to cover all organisms causing ocular infections,” she said. “Some thought has to be given to whether this is one of the more resistant organisms and determine if cultures, scrapings, etc. are needed to determine the pathogen in order to optimize treatment.”

Next: Providing the big picture

Ongoing surveillance studies, such as ARMOR, provide the big picture, Dr. Asbell said, by revealing trends to alert clinicians. However when it comes to treating individual patients, clinical judgment and findings from a local laboratory tests will also be necessary.

Penny A. Asbell, MD

E: penny.asbell@mssm.edu

This article was adapted from a poster presentation at the 2015 meeting of the Association for Research in Vision and Ophthalmology. Dr. Asbell did not report any relevant commercial relationships.