Antimicrobial susceptibility patterns of bacteria isolated from patients with ear discharge in Jimma Town, Southwest, Ethiopia

In the present study, the highest percentage of ear infection was found among pediatric patients (63%) and this agrees with reports from other parts of Ethiopia [3, 4, 1417]. In addition, the majority of bacterial isolates were identified in the age group < 4 years (41.61%) which is also in line with other previous studies [4, 15, 16, 18, 19], although a study done in Dessie (Ethiopia) reported higher frequency in the age group of 16–35 years (42.4%) [20].

In this study, the majority of the patients (57.8%) had ear discharge for ≥14 days, which is in agreement with previously done studies in Ethiopia, in which COM accounted for 60–83% of the OM cases [3, 4, 21, 22]. In the present study, the bacterial isolation rate was 92.5% which was higher than previous studies reported from Hawassa, 52.1% [14], Bahir Dar 80.4% [23], Nigeria 81.9% [24], Dessie 82% [16], Wollo 83.6% [20], Gondar 89.5% [15], Dessie 89.4% [3] and lower than the reports from Mekelle 98.2% [4], and Jimma 100% [22].

In the present study, from the total bacterial isolates, gram-negative bacteria (56.4%) were slightly higher than gram-positive bacteria, which is in agreement with previous studies done in various parts of Ethiopia: Mekelle (56%), Gondar (56.4%), Bahir Dar (58.8%), Addis Ababa (60.5%), Dessie (74.2%) and (78.7%), Wollo (75.8%) and Hawassa (79.5%) [3, 4, 1416, 18, 20, 23]. The leading isolated bacteria in this study was S. aureus (30.72%), followed by Proteus spp. (17.89%) and P. aeruginosa (10.61%), similar to reports of other investigators from Mekelle and Addis Ababa [4, 18]. Unlike our findings, Proteus spp. followed by S. aureus and Pseudomonas spp. were the predominant isolates reported by other researchers from different parts of Ethiopia [3, 15, 16, 20, 22] and relatively different patterns were reported from elsewhere [2527] with P. aeruginosa as the main isolate followed by S. aureus and Proteus spp. The possible reasons for such variation in the bacterial profile might be attributed to the difference in climatic and geographic variation of the study sites.

In our study, the most prevalent organism responsible for acute ear infection was S. aureus (37.5%). Even though, the global reports show that H. influenzae, S. pneumoniae, and M. catarrhalis to be the most prevalent organisms responsible for AOM [3], our findings is in agreement with reports from other African countries that indicate S. aureus and S. pyogenes were the predominant isolates [28]. The reason for this might be the differences in geographic location, prevalence of respiratory infection, coverage of pneumococcal conjugate vaccine (PCV), and possible overuse of antimicrobials that might have killed the sensitive organism and favored the drug resistant ones to be predominant, biofilm phenotypes property of the S. aureus and potentially other local and regional factors.

In the present study, both Proteus spp. (P. vulgaris (p = 0.018) and P. mirabilis (p = 0.037)) (84.4%) were more common among the chronic than the acute ear infections. This finding is comparable to Seid et al. from Dessie [3] and Muleta et al. from Jimma [22] who reported rates of 85.4 and 74.5%, respectively and contradicts with Wasihun and Zemene’s from Mekele [4] who reported that P. mirabilis was seen in 63% of COM and P. vulgaris in 57% of AOM. The possible reasons for this might be Proteus spp. were common isolates in patients presenting lately (2 months after onset of ear discharge), as a result patients with discharging ears may not notice immediately for early diagnosis or the antibiotic treatment was not effective [29].

In this study, those with history of previous health care visit and treatments (58.96%) showed a significant association with chronic ear infection (p = 0.000), which is similar to Wasihun’s and Zemene’s reports [4]. This could probably be due to failure of empiric treatment of AOM. Thus, it might be wise to take a swab if the patient has ear discharge, then begin treating the patient with topical +/− systemic antibiotics according to empirical guidance available. In the meantime, proper etiology based diagnosis should be in place and once the organism is known, appropriate management of ear infection becomes effective. This in turn facilitates the rational use of antibiotics based on recent and local data in our health facilities in order to reduce sequales associated with ear infection [1]. In this study, the isolated bacteria showed highest rate of resistance to the different antibiotics commonly used for OM treatment which is in line with earlier reports from different parts of Ethiopia [3, 4, 16, 20] and a good overall antimicrobial susceptibility pattern (> 70%) was seen to gentamicin and ciprofloxacin which is also in line with other studies conducted in Ethiopia [3, 4, 16, 20, 23] and in other countries asuch as Ardebil [30], Iraq [31], Nepal [32], India [33], and Jordan [34]). In contrast to these reports, gentamicin and ciprofloxacin were reported as ineffective from a study conducted in Nigeria [24].

In the present study, 34.5% of S. aureus were MRSA, similar to a report by Hailu et al. (34.6%) from Bahir Dar [23]. On the other hand, S. aureus exhibited high levels of resistance to ciprofloxacin (27.3%) which is significantly higher compared with other reports which showed resistance rates as high as 21% [3, 4, 15, 16, 23]. Many of the isolates showed high levels of sensitivity to gentamicin, which is consistent with other reports [1416]. Moreover, the observed high level of resistance for clindamycin (43.6%), erythromycin (58.2%) and trimethoprim-sulphamethoxazole (80%) is also higher than other studies [3, 4, 15, 16, 22].

Overall, 67% of the bacterial isolates from this study were characterized as MDR pathogenic bacteria. The reason for this might be linked to a prescription of antibiotics without laboratory guidance, purchasing of drugs without proper prescription (self-medication) in the local pharmacies and drug stores, misuse of antibiotics, indiscriminate use of antibiotics including animal husbandry, inappropriate prescribing habits and an over-zealous desire to treat every infection using antibacterial agents. Moreover, biofilm bacterial properties of common isolates, unavailability of bacterial culture facilities and poor infection prevention and control practices may be some of the different factors that can contribute to the development of MDR among these isolates.

The limitations of this study include the fact that we did not include the OME and OM without discharge as well as the fact that we did not try to isolate strict anaerobic bacteria and fungi which might also be the possible causative agents for OM. Additionally, we didn’t intend to differentiate OM from otitis externa.

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