Genotypic Resistance Analysis of Bacterial Species Involved in Infectious Keratitis

Background/Objectives: Infectious keratitis represents a major ophthalmological emergency and a leading cause of corneal blindness worldwide. Rapid progression, frequent antimicrobial resistance, and poor therapeutic outcomes make genotypic surveillance essential. This study aimed to analyze the distribution of bacterial pathogens involved in infectious keratitis and characterize their resistance mechanisms at the genotypic level, with emphasis on extended-spectrum β-lactamase (ESBL) genes. Methods: Corneal scrapings were collected from patients diagnosed with bacterial keratitis at the County Clinical Emergency Hospital of Craiova. Isolates were identified using standard microbiological techniques, followed by antimicrobial susceptibility testing. Genotypic resistance markers, including tem, shv, and ctx-M gene families, were investigated using PCR-based methods, while phenotypic resistance was investigated using the Vitek2 system. Results: Gram-positive bacteria were the predominant isolates, with coagulase-negative staphylococci and Staphylococcus aureus accounting for most cases. Among Gram-negative pathogens, Pseudomonas aeruginosa and Enterobacteriaceae were frequently detected. Genotypic analysis revealed tem genes in a substantial proportion of ocular isolates, often plasmid-mediated, while shv genes showed low prevalence and ctx-M genes were less frequent. The genetic determinants correlated well with phenotypic resistance expressed by MICs. Conclusions: The study highlights the significant correlation between genotypic markers and resistance phenotypes in bacterial keratitis. Continuous molecular surveillance is essential to guide targeted therapy, prevent therapeutic failure, and improve patient outcomes in infectious keratitis.