# Genetic Characterization and Biofilm-Forming Capacity of Bacterial Population Isolated from Conjunctival Samples

## TL;DR

This study analyzed bacteria from conjunctival samples, finding that many are drug-resistant and form biofilms, which may reduce treatment effectiveness.

## Contribution

The study links resistance genes to biofilm formation in conjunctival bacteria, emphasizing biofilm-related antimicrobial resistance in clinical settings.

## Key findings

- Gram-positive cocci, especially Staphylococcus epidermidis, were the most common and multidrug-resistant isolates.
- Biofilm formation was more prevalent in Gram-negative bacteria, though Gram-positive biofilms showed higher antimicrobial tolerance.
- Biofilm-embedded bacteria exhibited increased resistance to amikacin and levofloxacin, particularly in Staphylococcus species.

## Abstract

Background/Objectives: Bacterial conjunctivitis is a common ocular infection requiring prompt treatment, particularly in vulnerable patients, and may influence perioperative outcomes. This study aimed to characterize conjunctival bacterial isolates phenotypically and genotypically, to evaluate their biofilm-forming capacity, and to investigate the relationship between resistance gene carriage, resistance phenotypes, and biofilm-associated antimicrobial resistance (AMR). Methods: A prospective, single-center, cross-sectional study was conducted on bacterial isolates from conjunctival samples of patients examined in an ophthalmology department. Antimicrobial susceptibility testing (AST) was performed to determine the minimum inhibitory concentrations (MICs). Resistance genes were detected by quantitative PCR. Biofilm-forming capacity was assessed using the microtiter plate assay, and biofilm susceptibility to amikacin (AK) and levofloxacin (LEV) was evaluated using a biofilm susceptibility assay. Results: A total of 78 isolates were analyzed; Gram-positive cocci prevailed (GPC, 84.6%), being significantly more frequent than Gram-negative bacilli (GNB, p < 0.001). Among GPC, 65.2% were multidrug-resistant, with Staphylococcus epidermidis emerging as the most frequent species (p < 0.001). Resistance gene carriage was detected in 33.3% of GNB. Strong biofilm formation was observed in 22.7% of GPC versus 58.3% of GNB. It should be noted that the relatively small number of GNB may limit the statistical robustness of comparisons between Gram-positive and Gram-negative groups. A statistically significant association between resistance genes and biofilm capacity was found only in Staphylococcus aureus (p = 0.027). Biofilm-embedded bacteria showed increased antimicrobial tolerance, particularly for AK in S. aureus and for both AK and LEV in S. epidermidis (p < 0.001). Conclusions: The prevalence of multidrug-resistant conjunctival isolates and their biofilm-forming capacity highlights the clinical importance of biofilm-related resistance and support integrating AMR profiling with biofilm assessment to optimize empirical therapy in bacterial conjunctivitis.