Trends in aetiology and antibiotic resistance in bacterial keratitis isolates from South India between 2013-2024

Aim: To measure aetiology and antibiotic resistance (AMR) trends of bacteria cultured from corneal scrapings from patients with infectious keratitis at a tertiary referral hospital in South India. Methods: In this retrospective study, bacterial aetiology and antimicrobial resistance profiles were identified from the microbiology records of patients undergoing microbial keratitis diagnosis at the Aravind Eye Hospital, Madurai, India from 2013-2024. Statistical analyses were performed by Spearman's rank correlation coefficient to identify significant trends. Results: P. aeruginosa (n=1047) was the most frequently isolated bacteria, followed by S. pneumoniae (n=987). There were significant increases in the number of P. aeruginosa (rs: 0.66; P=0.0219) and S. aureus isolates cultured (rs: 0.70; P=0.0130). S. aureus demonstrated increasing resistance to cefazolin (rs: 0.76; P=0.0015), gatifloxacin (rs: 0.75; P=0.0071), levofloxacin (rs: 0.60; P=0.0442), moxifloxacin (rs: 0.59; P=0.0437) and chloramphenicol (rs: 0.78; P=0.0049) over time. S. pneumoniae resistance towards tetracycline significantly increased (rs: 0.80; P=0.0029). P. aeruginosa isolates remained largely susceptible to all antibiotics screened, with significant decreasing resistance rates to ceftazidime (rs: -0.71; P=0.019), amikacin (rs: -0.59; P=0.0489), gentamicin (rs: -0.66; P=0.0219) and tobramycin (rs: -0.69; P=0.017) identified. No significant trends in resistance patterns were identified for Nocardia spp.. Conclusion: Bacterial aetiology and antibiotic resistance rates shifted over time for key pathogens causing keratitis. Understanding these in the local context is important. For instance, while others in India have reported increasing P. aeruginosa AMR, we did not find this to be true in our patient population. This may have implications for local prescribing guidelines.