Study Details Antibiotic Resistance Among Ocular Microorganisms

Between 2009 and 2018, trends in antibiotic resistance among ocular microorganisms remained mostly unchanged in the United States, according to a study published in JAMA Ophthalmology. However, multidrug resistance (MDR), especially among methicillin-resistant staphylococci, remained high throughout the study period.

In this cross-sectional study, researchers evaluated data from the ongoing Antibiotic Resistance Monitoring in Ocular Microorganisms (ARMOR) study. Minimum inhibitory concentrations were determined to assess the antibiotic resistance profiles of over 6000 ocular isolates of Staphylococcus aureus (S aureus), coagulase-negative staphylococci (CoNS), Streptococcus pneumoniae (S Pneumoniae), Pseudomonas aeruginosa (P aeruginosa), and Haemophilus influenzae (H influenzae).

Discoveries of significant antibiotic resistance among ocular pathogens over the past 2 decades prompt concern among ophthalmologists, as resistance can result in treatment failure and complicate antibiotic choice in clinical practice.

Using ARMOR data from community hospitals, academic hospitals, specialty or ocular centers, and reference laboratories, researchers “assessed the overall antibiotic resistance profiles and trends by age, geographic region, and over time for ocular isolates.”

Testing representative antibiotics from 10 different classes, investigators calculated the lowest drug concentrations that inhibited the growth of 90% of indicated isolates (MIC90s).

In total, 6091 isolates (2189 S aureus, 1765 CoNS, 590 S pneumoniae, 767 P aeruginosa, and 780 H influenzae) were collected from 88 sites across 41 states.

The study yielded the following results:

• 765 S aureus (34.9%) and 871 CoNS (49.3%) isolates were methicillin resistant and more likely to be concurrently resistant to macrolides (azithromycin: S aureus: odds ratio [OR], 18.34 [95% CI, 13.64-24.67]; CoNS: OR, 4.59 [95% CI, 3.72-5.66]), fluoroquinolones (ciprofloxacin: S aureus: OR, 22.61 [95% CI, 17.96-28.47]; CoNS: OR, 9.73 [95% CI, 7.63-12.40]), and aminoglycosides (tobramycin: S aureus: OR, 18.29 [95% CI, 13.21-25.32]; CoNS: OR, 6.28 [95% CI, 4.61-8.56]) compared with methicillin-susceptible isolates (P < .001 for all)
• MDR was observed among methicillin-resistant S aureus (577 [75.4%]) and CoNS (642 [73.7%]) isolates
• Antibiotic resistance among S pneumoniae isolates was highest for azithromycin (214 [36.3%]), whereas P aeruginosa and H influenzae isolates showed low resistance overall
• Small changes in antibiotic resistance were noted over time (≤2.5% per year)

In addition, researchers found differences in antibiotic resistance among isolates varied by patient age and geographic location. “Higher rates of mean percentage of resistance and methicillin resistance were seen among staphylococcal isolates obtained from older patients,” authors note. Because older patients spend more time in hospitals or nursing homes, they may be more likely to be exposed to antibiotic-resistant bacteria.

Due to the relatively infrequent culturing of ocular pathogens during routine practice and the sites’ selection of isolates for submission, investigators note sampling bias may inhibit the generalizability of the data.

“Overall, 1 in 3 S aureus isolates and 1 in 2 CoNS isolates were resistant to methicillin and approximately 3 in 4 methicillin-resistant staphylococcal isolates were MDR,” researchers conclude. These findings should be taken into consideration when treating staphylococcal ocular infections, especially in older patients, they note.

Reference:

Asbell PA, Sanfilippo CM, Sahm DF, et al. Trends in antibiotic resistance among ocular microorganisms in the United States from 2009 to 2018. JAMA Ophthalmol. Published online April 9, 2020. doi:10.1001/jamaophthalmol.2020.0155