Prevalence and Antimicrobial Susceptibility Pattern of Methicillin Resistant Staphylococcus Aureus Isolated from Clinical Samples At Yekatit 12 Hospital Medical College, Addis Ababa, Ethiopia

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Addis Ababa University


Background: Staphylococcus aureus particularly MRSA strains are one of the major causes of community and hospital acquired bacterial infections. They are also becoming increasingly multi- drug resistant, and have recently developed resistance to vancomycin, which has been used successfully to treat MRSA for many years. In-vitro determination of drug resistance patterns of S. aureus is critical for the selection of effective drugs for the treatment of staphylococci infections. Objective: The aim of this study was to determine the prevalence of MRSA and MSSA strains isolated from different clinical specimens from patients referred for routine culture and sensitivity testing and also to define the antimicrobial susceptibility pattern of the strains. Method: A cross sectional study was conducted among 1360 study participants selected conveniently at Yekatit 12 Hospital Medical College from September 2013 to April 2014. Clinical samples from various anatomical sites of the study subjects were collected by employing standard microbiological techniques. Clinical samples were cultured on blood agar and mannitol salt agar and incubated at 35 -370C aerobically for 18-24 hours. Cultures with typical characteristics of staphylococci were identified to S. aureus by using DNAse test. S. aureus isolates then were screened for MRSA by using 1g oxacillin disc. The drug susceptibility patterns of both MRSA and MSSA to twelve antibacterial drugs were determined by disc diffusion procedure. All S. aureus isolates examined for beta-lactamase production by employing nitrocefin. Data were coded, entered and analyzed using SPSS version 16 software and logistic regressions were applied to assess any association between dependent and independent variables. P values < 0.05 were taken as statistically significant. Results: Of the1360 clinical specimens analyzed S. aureus was recovered from 194 (14.3%). The prevalence of S. aurues was higher in males than females 106 (54.6%) versus 88 (45.4%) and in patients with age group of 25-44 years 64 (33.0%). However, the isolation rate of S. aureus was not significantly associated with sex (p = 0.77) and age group (p > 0.05) Rate of isolation of S. aureus with regards to clinical specimens was the highest in pus 118 (60.8 %) and the lowest in sputum 1 (0.5%). Out of 194 S. aureus isolates, 34 (17.5%) were found out to be MRSA and the remaining 160 (82.5%) were MSSA. Relatively a higher MRSA was observed in males than females 19 (55.9%) versus 15 (44.1%) and in the age group 25-44 years 12 (35.3%). No significant association was observed between MRSA and sex (p= 0.87) and age groups (p> 0.05). Ninety eight (50.5%) S. aureus were multi-resistant (resistant to three or more antimicrobial agents) and isolates were more resistant to penicillin 187(96.4%) and least resistant for vancomycin 10(5.1%) and cephalothin 6(3.0%). MRSA stains were 100% resistant to penicillin G, erythromycin, trimethoprim-sulfamethoxazole and least resistant to vancomycin 10(29.4%) and cephalothin 6(17.6%). Out of 194 S. aureus isolates 153 (79%) were beta-lactames producers. Furthermore, of 34 MRSA isolates 30 (88.2%) and out of 160 MSSA strains 123 (76.8%) produced beta-lactamase. Conclusion: In this study Staphylococcus aureus isolates exhibited very high degree of resistance to different antibiotics. The isolates were also multidrug resistant to several combinations of the tested antibiotics. The emergence of vancomycin resistant S. aureus highlights the value of prudent prescribing of antibiotics (including vancomycin) and avoiding their irrational use



Yekatit 12 Hospital Medical College