Phenotypic and genotypic detection of clinical staphylococcus aureus isolates and their ability to form biofilm under different antibiotics

Staphylococcus aureus is the main pathogen, which can harm tissues, causing severe chronic, and recurrent infections that need extended antimicrobial therapy. Methicillin-resistant S. aureus's (MRSA) ability to produce biofilm is promoting the bacteria's spread and making it difficult to treat. Bacterial biofilm formation is frequently enhanced in the existence of antibiotics with sub-minimum inhibition concentrations (sub –MICs). The study aimed to evaluate the effectiveness of sub-inhibitory concentrations of antibiotics on biofilm formation. In a cross-sectional plan, a total of 40 S. aureus were isolated in Erbil hospitals from July to November 2023. Identification of isolates was carried out by the standard methods, the Vitek®2 system, the nuc gene, and 16S rRNA with specific primers. All isolates were tested for sensitivity toward 18 antibiotics using the common disc diffusion technique and Vitek®2 system. Biofilm formation by all the isolates was estimated by tube adherent and micro plate methods. The induction of biofilm by 1/2 and 1/4 MIC of four antibiotics were determined by a crystal violet assay. All the obtained data were statistically analyzed by GraphPad prism and SPSS programs. The study revealed that S. aureus had a high resistance to benzylpenicillin (90%), cefoxitin (75%), oxacillin (67.5%), erythromycin (52.5%), and clindamycin (50%). Screening for MRSA showed that 75% of the isolates were MRSA. For biofilm production (40%), (32.5%), and (12.5%) of isolates were strongly, moderately, and weakly positive, respectively, and (15%) didn't show biofilm formation. In the selected 10 strains, biofilm formation increased in an average from 35% to 55% by using 1/2 MIC and 1/4 MIC of the antibiotics. Our findings concluded that the effect of sub-MICs of various antibiotics on biofilm formation may make treatment difficult and lead to the creation of chronic infections.