Conjunctival bacterial flora and antimicrobial susceptibility in bacterial pathogens isolated prior to cataract...

To optimize prophylactic antibiotic administration, antibiotic susceptibility before cataract surgery was investigated using ocular bacteria isolated preoperatively.

Retrospective cross-sectional study.

In 204 eyes of 102 patients who underwent routine bilateral cataract surgery, conjunctival sac scrapings were collected 1-2 weeks before surgery. A total of 192 major pathogens among the 470 isolated bacteria were subjected to susceptibility testing. The major pathogens included Staphylococcus aureus, Staphylococcus epidermidis, coagulase-negative staphylococci (CNS) other than S. epidermidis, Enterococcus faecalis, and Streptococcus spp. The following antibiotics were tested: cefmenoxime (CMX), ceftazidime (CAZ), tobramycin (TOB), vancomycin (VAN), erythromycin (EM), moxifloxacin (MFLX), gatifloxacin (GFLX), levofloxacin (LVFX), chloramphenicol (CP), and imipenem (IP).

The proportions of isolates with minimum inhibitory concentration (MIC) of S. epidermidis (N = 82), exceeding 4 μg/ml were high for CAZ (95.1%), EM (32.9%), LVFX (39.0%), and CP (82.9%). Susceptible (S) proportion was high for CMX (98.8%), VAN (100%), CP (93.9%), and IP (97.6%) but relatively low for MFLX (59.8%), GFLX (54.9%), and LVFX (54.9%). The MIC₉₀ values were high for CMX (16 μg/ml), CAZ (64 μg/ml), TOB (32 μg/ml), EM (128 μg/ml), LVFX (16 μg/ml), and CP (8 μg/ml). The MIC of quinolonesof pathogenic bacteria other than S.epidermidis (N = 108), exceeded 4 μg/ml for 11 isolates, including two Methicillin-resistant Staphylococcus aureus.

The increase in resistance of resident bacteria present in the conjunctival sac to antibiotics indicates that systemic and topical antibiotics are no longer effective, especially against external organisms affecting the eye.