Effect of prophylactic antibiotics on antimicrobial resistance of viridans streptococci in the normal flora of cataract surgery patients.

PURPOSE: To evaluate the effect of prophylactic treatment including vancomycin in the irrigating solution and topical chloramphenicol on antimicrobial resistance in viridans-group streptococci in the normal flora of patients having cataract surgery.

SETTING

Department of Ophthalmology, Turku University Central Hospital and Antimicrobial Research Laboratory, National Public Health Institute, Turku, Finland.

METHODS

Minimal inhibitory concentrations (MICs) of 15 antimicrobials were determined for 529 viridans streptococci isolated from throat, nasopharyngeal, and conjunctival swabs of 23 patients on 4 sampling occasions: before cataract surgery and 1 day, 1 month, and 3 months after surgery. Resistance mechanisms of erythromycin-resistant isolates were studied by the double-disk test and polymerase chain reaction of resistance genes.

RESULTS

No statistically significant changes occurred in the proportions of isolates with elevated MICs between different sampling occasions. Resistance to vancomycin or chloramphenicol was not found. Resistance to tetracycline, erythromycin, penicillin, quinupristin-dalfopristin, clindamycin, levofloxacin, and moxifloxacin was found on different sampling occasions in 27.9% to 38.7%, 13.1% to 21.8%, 11.5% to 19.4%, 8.9% to 16.9%, 2.3% to 5.6%, 0% to 2.4%, and 0% to 2.2% of the isolates, respectively. Of the erythromycin-resistant isolates, 80.8% had the M phenotype and mefA gene and 19.2% has the macrolide-lincosamide-streptogramin B phenotype and ermB gene.

CONCLUSIONS

Development of resistance of viridans streptococci in the normal flora to vancomycin and chloramphenicol during prophylactic use with uneventful cataract surgery is unlikely; the effect on resistance patterns of other antimicrobials is minor. Routine use of prophylactic vancomycin is discouraged, however, because of the lack of scientific proof of its efficacy in preventing postoperative endophthalmitis.