Abstract
Background:
Opportunistic Staphylococcus aureus (S. aureus) may cause a range of infections in humans and animals, from self-limiting to life-threatening. S. aureus might be acquired from food via contaminated hands or food contact surfaces. Orange peel extract has various therapeutic uses.

Aim:
This study aimed to estimate the antibacterial activity of orange peel extract against Staphylococcus aureus (S. aureus) in vitro by measuring the inhibition zone and MIC.

Methods:
Staphylococcus aureus was isolated from food contact surfaces on mannitol salt agar in Kufa, Iraq. An aqueous extract of orange peel was prepared. The antimicrobial activities of the orange peel extracts against the recovered S. aureus isolates were tested using the agar well diffusion method by measuring the diameters of the inhibition zone on nutrient agar.

Results:
The results showed significant antibacterial activity (P<0.05) of orange peels extract at different concentrations. All tested concentrations (10-100 mg/ml) had clear antimicrobial activities against S. aureus. The minimum inhibitory concentration recorded was 10 mg/mL. Such antimicrobial activities were comparable to those of the tested antimicrobials, such as trimethoprim, vancomycin, ciprofloxacin, and chloramphenicol. The lowest anti-S. aureus activities were recorded for azithromycin and clindamycin, with no anti-S. aureus activity for tobramycin.

Conclusion:
Orange peel extract had antibacterial activity against S. aureus. The correlation of the exponential increase in the diameter of the inhibition zone with increasing the extract concentrations of orange peel extract was well-marked. Therefore, orange peel extracts can be used in food preparations and hand washes to inhibit S. aureus growth.

Key words: Orange peel extract; Staphylococcus aureus; Antibacterial activity; Antibiotics; Minimum inhibitory concentrations.