Rising fluoroquinolone resistance rates in corneal isolates: implications for the wider use of antibiotics within the community

Abstract

Objective

To examine microorganisms and their antibiotic susceptibility from corneal specimens for community-acquired microbial keratitis at the Royal Victorian Eye and Ear Hospital.

Methods

A retrospective review of microbiological results from January to April 2014 was undertaken. Patients’ medical records were identified from the hospital's dispensing records of ofloxacin eye drops. Corresponding microbiology results from corneal specimens (species of isolated organisms and antibiotic susceptibilities) were recorded.

Results

There were 164 patients included in the study, of which 85 cultured positive, typical for corneal specimens. Of these, 75% were Gram-positive bacteria, 16% Gram-negative and 2% fungi. The commonest organisms were Staphylococcus sp. (46%) and Streptococcus sp. (10%). Of the 76 cases where fluoroquinolone susceptibility was tested, five (6.6%) demonstrated antibiotic resistance (minimal inhibitory concentration≥4.0 μg/mL), significantly higher than the 0% reported in 2000 (P = 0.002). All Staphylococcus isolates resistant to ciprofloxacin were resistant to cefazolin but susceptible to vancomycin. In ciprofloxacin-resistant isolates of streptococci, susceptibility to cefazolin and vancomycin was observed.

Conclusions

Most organisms identified on corneal specimens were Gram-positive. Susceptibility to fluoroquinolones was still high, although a trend for increasing ciprofloxacin resistance was noted. Further investigation is necessary to investigate if this reflects a wider antibiotic resistance prevalent within the community.