Prevalence and Possible Predictors of Drug-Resistant Pseudomonas aeruginosa in External Ocular Infections: A Single-Center, Retrospective, Cross-Sectional Study

Objective Ocular infections due to multi-drug-resistant Pseudomonas aeruginosa (MDRP) have been reported in recent years. This study was undertaken to determine the culture-positivity rate of P. aeruginosa and drug resistance among patients with suspected external ocular infections and to predict systemic risk factors for drug resistance in P. aeruginosa. Methods This retrospective, single-center, cross-sectional study involved 781 consecutive patients who provided samples for aerobic culture to test for a suspected external ocular infection. DRP was defined as a strain resistant to one or two of three antibiotics, levofloxacin, gentamicin, and imipenem; MDRP was defined as that which was resistant to all three. Results Among 108 patients in whom gram-negative bacilli were observed, P. aeruginosa was isolated from nine patients, including three DRP-positive cases; no MDRP was isolated. P. aeruginosa was not isolated from those <69 years of age. Among patients in whom gram-negative bacilli were detected, the isolation rate of P. aeruginosa was 0 for patients aged ≤64 and 0.1 for those aged ≥65, indicating a significant difference. For patients with gram-negative bacilli, the DRP-positivity rate was significantly higher for hospitalized patients than outpatients. Thus, in addition to being geriatric, being hospitalized was a risk factor for DRP infection among patients with gram-negative bacilli. All the P. aeruginosa strains isolated were susceptible to colistin. Conclusions Our findings may suggest that once gram-negative bacilli are isolated in an elderly hospitalized patient, possible DRP infection and the topical use of colistin should be taken into consideration even before the results of culture and susceptibility testing are obtained.