S. aureus is a main pathogenic bacterium which causes severe human health problems globally (13), and its anti-microbial resistance characteristics has made it more rebellious in the health institutions (14).
The isolation rates of S. aureus in the current study was 139/1365 (10.2%) which is lower than a study conducted in Ethiopia, 79/94(84.0%) (15); Nigeria, 55/360 (15.3%), and the occurrence of S. aureus was the highest in wound swabs (16), but in the present study, the highest isolates was recovered from blood sample followed by wound specimen.
Majority of the isolates were recovered from patients age less than 5 years, 51(36.7%), followed by 16-30 years, 42 (30.2%) while the least number of isolates were from patients greater than 60 years. This is in line with an observation from previous Ethiopian report where the rate of isolation of S. aureus was higher in lower age (15–24 years), 46/210(21.9 %) (17), and in Eritrean study where it was significantly associated with lower age, 13 to 18 years, (78.6%) and <13 years old, (85.0%) and lower rate of isolation was recorded in older age (≥61years old) (18).
The most common clinical specimen for S. aureus isolates in the current study was blood 61 (43.9%) followed by wound, 45 (32.4). However, the previous study conducted in Ethiopia demonstrated that the highest rate of isolation was observed in pus, 118/213 (55.4 %) followed by nasal swab, 9/27(33.3%) (17); in Eritrea, highest isolates (64/103, 62.1%) were obtained from pus specimens examined followed by blood specimens 6/15 (40.0%) (18). The highest prevalence of S aureus was also observed from seminal fluid of patients, 9/36(25%) followed by wound swabs, 13/87(15%) while urine samples showed the least (5.4%) in a study from Nigeria (14). Another study conducted in Nigeria also revealed that the occurrence of S. aureus was highest in wound swabs, high vaginal swabs and urine (16). The Iranian report on distribution analysis of the S. aureus isolates among clinical samples showed that most isolates (29.0%) were recovered from the pus and the lowest (1.4%) was found from cerebrospinal fluid (12). The variations in occurrence of the organism in the different clinical samples across many studies shows the versatility of this organism amongst other bacteria which makes it the most endemic pathogen in clinical settings, and it may likely be responsible for various infection such as UTI, wound infection, deep tissue infections, including osteomyelitis, arthritis, endocarditis, and cerebral, pulmonary, renal and breast abscesses (19).
In the present study, the resistant rate of S. aureus isolates against 10 antibiotics were, 81(73.6%), 78(70.9%), 76(69%), 66(60%), 65(59.1%). 39(35.5%) and 39(35.5%), 38 (34.5%), 34(30.9%), and 24(21.8%) to penicillin, cotrimoxazole, ceftriaxone, erythromycin, tetracycline, chloramphenicol and ciprofloxacin, cefoxitin, gentamycin and clindamycin, respectively; which is almost in parallel with a study conducted in Ethiopia where the isolates were resistant to ampicillin (100%), cefoxitin (68.4%), clindamycin (63.3%), cephalothin (59.5%), tetracycline (57%), cotrimoxazole and bacitracin (53.2%, each), and erythromycin (51.9%) (15); and in Iran where the percentage of resistance of S. aureus were to 100 %, 59.1%, 57.7 %, 50 %, 49.1 %,, 48.3 %, 47.6 % and 47.6 %, 25 %, and 0.7 % to penicillin, tetracycline, ciprofloxacin, erythromycin,, gentamicin, co-trimoxazole, cefalotin and oxacillin, clindamaycin and vancomycin, respectively (12). The highest level of antimicrobial resistant S. aureus in a Nigerian study was 68% to ceftazidime followed by cloxacillin (48%) while the least resistance (26%) was observed for meropenem (14). In line with the current study, another study from Nigeria also demonstrated that the isolates from three hospitals were highly (>50%) resistant to all the antibiotics tested (Ampicillin, Ciprofloxacin, Erythromycin, Oxacillin, Rifampicin, Clindamycin, Sulphamethoxazole/Trimethoprim, and Streptomycin), but moderately (<40%) to gentamicin and levofloxacin (16). This variation might be attributed to differences in patients` hospital stay, level of infection control practices by health facilities, previous exposure of patients to antibiotics, irrational use of antibiotics.
Phenotypically, considering cefoxitin as surrogate marker for methicillin test, 38 (34.5%) of the isolates of S. aureus were methicillin resistant in the current study which is in agreement with the pooled prevalence of MRSA reported in Ethiopia, 32.5% (20). However, the current finding of MRSA is lower than a report from Ethiopia, where 54 (68.4%) of the isolates were MRSA (15); from Eritrea, 59(72.0%) of the isolates were MRSA (18); from Nigerian studies, 44.0% (14); and 40.4% (21); and from Iran 133/279 (47.6%) (12). On the other hand, the present report is higher than another previous report from Ethiopia where 34/194 (17.5 %) of the S. aureus isolates were found to be MRSA (17); and Iraq, MRSA prevalence was 114/429 (26.54%) (22). The possible explanation for the observed discrepancies across the literature might be associated with the variation of the methods used to detect methicillin resistance. Some studies used cefoxitin and others used oxacillin as a surrogate marker for detection of methicillin resistance.
The MDR isolates observed in the current study was 87/110 (79.1%) which is in line with a previous report in Ethiopia, 65(82.3%) (15). However, the MDR S. aureus observed in the present study is higher than a previous study reported from Ethiopia where 98(50.5%) of the S. aureus were MDR (17); in Eritrea, 17/43(39.5%) (18); and in Saudi Arabia where 47% of MRSA were MDR (23).
The PCR amplification result of mecA gene, a gene that confers resistance to methicillin and most β-lactam antibiotics, was done in 70 clinical isolates of S. aureus. However, among the total of 70 isolates, mecA gene was detected only in 14 (20.0%) S. aureus isolates with an amplicon of 533 bp considered as indicative with the presence of mecA gene. Although, its distribution is different, mecA gene producing MRSA were reported in all study sites. This is similar with a study from Nigeria that, phenotypic resistance to cefoxitin was 46.5%, while the mecA gene was 19.2% (21). Another study from Nigeria indicated that, S. aureus isolates with phenotypic resistance to methicillin (oxacillin) were tested for mecA gene and none of the isolates contained the mecA gene (24). As reported by Nwaogaraku et al from Nigeria showed that, all isolates of MRSA from blood samples of pigs were mecA negative on PCR (25). However, the present study is different from many studies done elsewhere (23, 26, 27). The possible explanation why phenotypically MRSA positive isolates did not show mecA gene might be due to loss of the mecA gene during prolonged storage (28) or other mechanisms other than the presence of mecA gene (mecC and mecB) responsible for methicillin resistant Staphylococcus aureus (29, 30).