Study Biofilm Phenotyping and Genotyping of Staphylococcus Aureus from the Nasal Discharge of Sheep in Basrah Governorate

Abstract

The study was designed to determine and characterize the rate of nasal discharge of S. aureus in sheep and to characterize it genotypically by PCR targeting the gene nuc and culturing. The study was conducted in Basrah province, between September and October 2025. The study evaluated phenotyping of biofilm formation by microtiter plate assay and genetic to biofilm genes from the isolated S. aureus among the 50 tested nasal swabs, 42 (84%) isolates were positive for S. aureus isolation using culturing. Antibiotic susceptibility testing for S. aureus was conducted utilizing the standard Kirby-Bauer disk diffusion method. A total of 32 biochemical methods were employed, accounting for 64% of the approaches used. The findings showed that 28 isolates, representing 56%, tested positive for the nuc gene at a size of 423 bp, thus confirming the successful amplification of the nuc gene and the presence of S. aureus. The S. aureus isolates were categorized into three groups of strong, medium and weak biofilm producers by the biofilm formation assay. Results showed that the rate of detection of biofilm genes in Staphylococcus aureus was 50%, 39.28% and 10.71%, The PCR analysis indicated that all isolates included the icaA gene, achieving a detection rate of 100%. The sigA gene exhibited the highest frequency of detection at 92.85%, while the katA gene was identified in 75% of the cases. The sodA gene had the lowest detection rate among the genes examined, at 69.23%. The isolates exhibited varying levels of resistance to the tested antibiotics; the highest resistance rate was recorded against azithromycin (92.85%), whereas all isolates showed complete susceptibility (100%) to oxacillin.
Furthermore, two isolates showed resistance to cefoxitin and were identified as methicillin-resistant Staphylococcus aureus (MRSA). The presence of S. aureus and MRSA in sheep is alarming, as these animals could act as a source of infection for humans, especially for those working on farms.