Evaluation of Antibiotic Susceptibility Pattern of Staphylococcus Aureus in Clinical Specimens of Patients Admitted to Ayatollah Mousavi Hospital in Zanjan Using Disk Diffusion, E.test and D-test Methods

Staphylococcus aureus is an important cause of severe infections in hospital and community and can cause significant mortality and morbidity in patients. In this study, the susceptibility and resistance pattern of Staphylococcus aureus to common antibiotics was investigated by disk diffusion, MIC (Minimal-inhibitory concentration) determination with E-test and D-test

This study was performed on 66 clinical specimens of Staphylococcus aureus from different wards of Ayatollah Mousavi Hospital in Zanjan for one and a half years. Sensitivity, intermediate susceptibility and resistance status of Staphylococcus aureus to antibiotics for cefazolin, cloxacillin, vancomycin, clindamycin, erythromycin and cotrimoxazole were determined by disk diffusion method. In cases where Staphylococcus aureus was susceptible to clindamycin but resistant to erythromycin, a D-Test was also performed to evaluate the inducible resistance to clindamycin. The frequency of methicillin-resistant Staphylococcus aureus in addition to disk diffusion method was also determined by MIC method.

Of 66 samples collected during one and a half years, all samples were sensitive to vancomycin. The sensitivity to co-trimoxazole was 90.9%, cefazolin 86.4%, clindamycin 81.8%, cloxacillin 71.2%. D-Test was positive in 5.5% of the samples. The frequency of methicillin-resistant Staphylococcus aureus in both E-test and disk diffusion methods was 28.8%. The highest rate of resistance was in the ICU ward (31.2%).

In this study, antibiotic resistance in general was less prevalent than in most other centers, which could be due to the higher prevalence of ulcer samples with lower resistance percentage or to avoid the administration of broad-spectrum antibiotics and more appropriate use of antibiotics in wards (other than intensive care units). Also, according to the D-Test method, there was no significant resistant induction of clindamycin in our center, so it can be used easily if the organism is sensitive.