Coliform bacterial contamination of dairy products and antimicrobial susceptibility patterns of common coliform bacterial isolates in Gondar-Bahir Dar milk shed, Northwest Ethiopia

Abstract

Abstract Background: Dairy products can be contaminated by pathogenic microorganisms due to unhygienic production and processing practices. Determining the status of the bacteriological contamination is vital to design evidence-based strategies to minimize the risk of infections and to enhance the quality and shelf life of processed products. This study was conducted to determine the status of contamination of dairy products with coliform bacteria and the antimicrobial susceptibility of common coliform bacterial isolates in the Gondar-Bahir Dar milkshed, Northwest Ethiopia. Methods: In total, 184 dairy product samples (raw milk (97), yoghurt (traditionally fermented milk) (48), buttermilk (9), traditionally prepared soft cheese (11), and pasteurized milk (19)) were collected. Of these, the coliform count was conducted on 146 samples (raw milk (97), yoghurt (6), buttermilk (6), traditionally prepared soft cheese (11), and pasteurized milk (19)) was assessed by coliform counts. Coliform bacteria were isolated from all 184 samples using standard bacteriological techniques and isolates were identified by the Analytical Profile Index (API) E 20 test. The antimicrobial susceptibility of the bacterial isolates was assessed by using the Kirby-Bauer disk diffusion method. Results: The average coliform count (CC) of samples was 5.6 log CFU/ml (confidence interval (CI)= 5.3 – 6.0). There was a significant (P<0.05) difference in the average CC among sample types, cleanness of the animals and hygiene of the containers. However, the differences in the average CC among sampling sites, farm size, source of water to clean milk containers, availability of cooling facilities, feed source, type of container, farm hygiene, and milker’s hygiene were not statistically significant. Out of examined 184 samples, 40.8, 33.7, 9.2, 12.5, and 1.6% were positive for E. coli, Citrobacter species (spp), Klebsiella spp, Enterobacterspp, and Serratia spp, respectively. Coliform bacteria isolates were more susceptible to third-generation cephalosporins like ceftazidime, ceftriaxone, and cefotaxime. However, they were relatively more resistant to cephalothin and ampicillin. Conclusion: most of the dairy product samples were highly contaminated by coliform bacteria and the isolates demonstrated a considerable rate of resistance. Therefore, hygienic measures should be enhanced to improve the bacteriological quality of dairy products in the study area, and strategies need to be designed to reduce the proliferation and spread of resistant strains to minimize public health risks.