Antimicrobial susceptibility patterns of E . coli from clinical sources in northeast Ethiopia

Background: Escherichia coli is the leading cause of urinary tract, ear, wound and other infections in humans. Increasing rates of antimicrobial resistance among E. coli is a growing concern worldwide. Objectives: The aim of this study was to determine the prevalence and antimicrobial susceptibility of E. coli from clinical


Introduction
Escherichia coli is a common inhabitant of the human and animal gut, but can also be found in water, soil and vegetation.It is the leading pathogen causing urinary tract infections 1,2,3 and is among the most common pathogens causing blood stream infections 4 , wounds, otitis media and other complications in humans 5,6 .E. coli is also the most common cause of food and water-borne human diarrhea worldwide and in developing countries, causing many deaths in children under the age of five years 7 .
Antimicrobial resistance in E. coli has been reported worldwide and increasing rates of resistance among E. coli is a growing concern in both developed and developing countries 8,9 .A rise in bacterial resistance to antibiotics complicates treatment of infections.In general, up to 95 % of cases with severe symptoms are treated without bacteriological investigation 10 .Occurrence and susceptibility profiles of E. coli show substantial geographic variations as well as significant differences in various populations and environments 11 .In Ethiopia, a number of studies have been done on the prevalence and antimicrobial resistance patterns of E. coli from various clinical sources 5,12,13 .The aim of this study was to determine antimicrobial susceptibility of E. coli from clinical sources at Dessie Regional Health Research Laboratory.

Study design
A retrospective review was done on results of cultures of urine, ear discharge, pus swab from wounds, and eye discharge that had been performed from 2003 -2010 at Dessie Regional Health Research Laboratory.The sex and age of patients.As well as E. coli isolates and antimicrobial susceptibility data were collected from the registration records using a standard data collection form.

Culture and identification
The specimens were collected from public and private hospitals and health centers.As the standard operation procedures show, clean-catch midstream morning urine specimens are collected using sterile wide mouth glass containers.Urine samples were plated on Cystine Lactose Electrolyte-Deficient medium (CLED), MacConkey agar and, Blood agar (Oxoid, Basingstoke, UK) using calibrated wire loops and then incubated aerobic atmosphere at 37 o C for 24 hours.From positive cultures, uropathogens were identified according to the standard operational procedures as per the standard microbiological methods 14 .A significant bacterium was considered if urine culture yield < 10 5 colonyforming unit (CFU/ml. Samples from discharging ears, eye swab, and pus from wound were collected using sterile cotton swabs 14 .Specimens were inoculated onto 5% Sheep's blood agar, chocolate agar, mannitol salt agar and MacConkey agar plates (Oxoid Ltd, Basing stoke Hampshire, UK).The plates were incubated at 37 o C aerobically and examined after 24 and 48 hours.

Statistical analysis
The chi-square test was employed to compare the proportion of bacterial isolates with patient sex and age; and comparison of antimicrobial resistances.P-value of < 0.05 was considered to indicate statistically significant differences.

Ethical consideration
Ethical approval was secured from Research Ethics Committee of Bahir Dar University.Permission from Dessie Regional Health Research Laboratory was also obtained.

Discussion
Antimicrobial resistance in E. coli has increased worldwide and its susceptibility patterns show substantial geographic variation as well as differences in population and environment 17 .The isolation rate of E. coli in the present study was 14.2% and it was commonly isolated from urine samples (45.5%).These findings are in conformity with reports by other researchers 13,18,19 .
In this study, the overall resistance of E. coli to antimicrobials was high.The result is consistent with the findings of previous studies 20 .The resistance rates recorded in this study are higher than the results of Khan et al. 6 and lower than the results of Iqbal and Patel 21 and Okonko et al. 22 .High level of resistance in E. coli was reported to tetracycline from a study conducted in Ethiopia 23 and to erythromycin from a study done in Slovenia 24 .
In all clinical samples, E. coli showed high resistance rates of > 80% to erythromycin and amoxicillin and > 60% to tetracycline.The results of this study are in line with the findings of other studies conducted in different parts of the world 25,26 .However, the antimicrobial resistance rates obtained in this study were higher compared to susceptibility patterns reported from previous studies 27,28,29 .
E. coli isolates were sensitive to gentamicin, nitrofurantoin, ciprofloxacin and chloramphenicol.Similar studies conducted in Ethiopia 30 and Nigeria 31 have reported comparable susceptibility rates.High sensitivity to ciprofloxacin and gentamicin and norfloxacin have been recorded from previous studies conducted in Nigeria and India 31,32 .In this study, norfloxacin, ciprofloxacin, gentamicin and chloramphenicol were found to be the most effective antimicrobials against E. coli isolates.
Furthermore n this study, a high rate of multiple antimicrobial resistance was recorded, which is consistent with the reports of studies done elsewhere 21,33 .The chi-square test for trend demonstrated increased resistance rates to all antimicrobials except ciprofloxacin.Increases in rates of resistance to different antimicrobials have been reported from previous studies conducted in different parts of the world 20,33,34 .

Conclusion
The results of this study show high rates of antimicrobial resistance to erythromycin, amoxicillin and tetracycline.Nitrofurantoin, norfloxacin gentamicin and ciprofloxacin are considered appropriate for empirical treatment of E. coli in the study area.Periodic monitoring of antimicrobial susceptibility both in the community and hospital settings is recommended.