Molecular Detection of fnbA, fnbB and nuc Genes and Phenotypic Detection of some Virulence Factors in Local Staphylococcus aureus Isolates.


In this study, Staphylococcus aureus (S. aureus) isolates (32) were collected from different hospitals in Baghdad and were diagnosed by conventional methods. Antimicrobial susceptibility test was performed by disc diffusion method for ten antibiotics. Hemolytic production activity and Deoxy ribonuclease (DNase) production ability were detected. The biofilm production ability was detected by microtiter plate method. The diagnosis was confirmed using PCR to detect the thermostable nuclease gene (nuc). Then, PCR technique was used to detect the fibronectin binding protein A and fibronectin binding protein B genes (fnbA and fnbB respectively).The results showed a high prevalence (78%) of Methicillin-resistant Staphylococcus aureus (MRSA) isolates, Imipenem and vancomycin were the most affective antibacterial agents tested. All isolates produced DNase enzyme . On blood agar plate, 65.6% of isolates produced β-hemolysis zones while (34.4%) of isolates did not produce any hemolytic zone. The results of biofilm production assay showed that 41% of isolates gave a weak positive results. All isolates (100%) that had been previously diagnosed as S. aureus by routinely used methods harbored the nuc gene. fnbA and fnbB were found in (100%) and (25%) of isolates respectively.Conclusion: Molecular detection of nuc gene by PCR has high specificity for identifying S. aureus with a low cost which requires less time as compared with biochemical methods. fnbA and fnbB genes are important virulence factors of S. aureus. fnbA gene is the highest prevalence of toxinogenic and can be used as a genetic marker for diagnosis of local S. aureus isolates while fnbB gene does not play an important role in infection of S. aureus.