Antimicrobial Resistance, Biofilm Formation, and Associated Genetic Determinants in Clinical Staphylococcus aureus Isolates: An Integrated Phenotypic and Genotypic Analysis

Abstract

Background: Staphylococcus aureus remains a major clinical pathogen due to its ability to acquire antimicrobial resistance and develop biofilms that enhance survival during infection. The coexistence of resistance determinants and biofilm-associated mechanisms represents a significant challenge for effective treatment and infection control. Objectives: The objective of this research was to determine the patterns of antimicrobial resistance, multi-drug resistance (MDR), biofilm formation ability, and presence of resistance and biofilm-related genes in clinical isolates of S. aureus.
Methods: A total of 100 confirmed S. aureus isolates recovered from different clinical specimens were investigated. Antimicrobial susceptibility testing was performed against selected antibiotics, and multidrug resistance (MDR) classification followed the standardized category-based definition. Biofilm production was evaluated using the microtiter plate method. Polymerase chain reaction (PCR) targeting the nuc gene was included as a species-confirmatory molecular assay, while mecA, ermC, icaA, and icaD were detected to characterize resistance- and biofilm-associated determinants. Statistical analysis evaluated associations between phenotypic and genotypic characteristics.
Results: Wound specimens represented the most frequent source of isolates (25%), followed by urine (17%). Cefoxitin showed the highest resistance rate (47%), while linezolid showed the lowest resistance rate, with 98% of isolates remaining susceptible. Half of the isolates were classified as MDR. Biofilm production was detected in 89% of isolates, with moderate biofilm production being the predominant phenotype (48%). The most frequently detected gene was icaD (72%), followed by icaA (62%), mecA (48%), and ermC (34%). Associations were observed between mecA and cefoxitin resistance (OR = 103.20, 95% CI: 26.02–409.27) and between ermC and erythromycin resistance (OR = 15.56, 95% CI: 5.63–42.99), both with p < 0.001. The icaD gene was also significantly associated with biofilm formation (OR = 16.58, 95% CI: 3.30–83.27; p < 0.001).
Conclusion: Clinical S. aureus isolates demonstrated a high prevalence of biofilm formation and considerable antimicrobial resistance. The coexistence of resistance and persistence-associated determinants highlights the need for integrated phenotypic and molecular surveillance strategies.