Prevalence and Spectrum of Conjunctival Bacterial Flora in Cataract Patients with and without Type 2 Diabetes Mellitus

Abstract

Background: Conjunctival commensal bacteria are a recognised source of postoperative endophthalmitis. Diabetes mellitus (DM) is associated with altered tear film, impaired immunity and a higher risk of ocular infection, yet data on its influence on conjunctival flora in cataract candidates remain sparse. Methods: In this cross-sectional study we prospectively enrolled 360 adults scheduled for cataract surgery at two tertiary centres in Hyderabad, India. Conjunctival swabs were obtained from the operative eye before instillation of any topical medication. Standard aerobic culture and biochemical identification were performed. Prevalence and species distribution were compared between type 2 diabetics (n = 160) and age-matched non-diabetics (n = 200). Results: Overall, 172/360 swabs (47.8 %) yielded bacterial growth. Culture positivity was significantly higher in diabetics (104/160; 60.5 %) than in non-diabetics (68/200; 34.0 %) (χ² = 22.9, p < 0.001). Gram-positive cocci predominated (163/172; 94.8 %). Staphylococcus epidermidis was the most frequent isolate (128/172; 74.4 %), followed by S. aureus (32/172; 18.6 %). Among diabetics, S. epidermidis (71.2 %) and S. aureus (17.3 %) remained dominant, but Gram-negative bacilli (mainly Pseudomonas aeruginosa) were more common than in non-diabetics (8.6 % vs 0 %; p = 0.002). Culture positivity correlated with poor glycaemic control (HbA1c ≥ 8 %, OR 2.1, 95 % CI 1.2-3.9) and longer diabetes duration (>10 years, OR 1.8, 95 % CI 1.0-3.2). Conclusion: Type 2 diabetes significantly increases both the prevalence and diversity of conjunctival bacterial flora in cataract patients, introducing additional Gram-negative pathogens of higher virulence. Targeted pre-operative antisepsis and individualised antibiotic prophylaxis may be advisable in this subgroup.