Bacteriological quality and antimicrobial resistance patterns of bacterial isolates from raw milk in dairy farms in Ethiopia

Abstract

Foodborne illness has a significant impact on public health and the economy, affecting nearly 30% of the population in developing countries annually. Infections transmitted through milk can lead to acute and severe diseases. However, there is inadequate information available regarding the bacteriological profile and antimicrobial resistance of microbial organisms present in raw milk. This study aimed to assess the bacteriological quality and antimicrobial resistance patterns of isolates from raw milk from different dairy farms in Ethiopia. A cross-sectional study was conducted in which 176 raw milk samples were selected through a multistage sampling technique from August 2022-April 2023. Bacteriological tests, including aerobic colony count, total coliform count, thermotolerant coliform count, Salmonella and Shigella detection, and Staphylococcus enumeration, were performed. Further bacterial identification was carried out via a VITEK-2 compact, whereas antimicrobial susceptibility was determined via the Kirby–Bauer disc-diffusion technique. Data analysis was conducted using SPSS V.27, which employs descriptive statistics and appropriate statistical tests. The mean aerobic colony counts were found to be 3.2 log 10 cfu/ml, and the total coliform count was 2.7 log cfu/ml. The mean thermotolerant coliform count was 2.69 log 10 cfu/ml and the E. coli count was 2.9 log 10 cfu/ml. The mean Staphylococcus count was 3.1 log 10 cfu/ml. Among the isolated strains, E. coli accounted for 77% of the total isolates, followed by S. aureus (13.6%), S. saprophyticus (9.8%), Klebsiella spp. (5%), and Salmonella spp. (1.4%). Antimicrobial susceptibility analysis revealed that Gram-negative isolates were susceptible to meropenem (96.8%) and ciprofloxacin (89.9%) but were resistant to tetracycline (62.2%) and streptomycin (62.2%). Staphylococcus isolates were 95.1% susceptible to levofloxacin and gentamycin, but 92.6% of the isolates were resistant to oxacillin. Additionally, 16.6% of the Gram-negative isolates produced extended-spectrum beta-lactamases, and 30% of the S. aureus isolates were resistant to methicillin. The findings of this study demonstrate that the quality of raw milk is unsatisfactory, as it contains pathogenic microorganisms and strains that are resistant to antibiotics. These results underscore the urgent need to implement robust control measures to improve production, storage, and processing practices. Effective measures are crucial to ensure the safety and integrity of the milk supply chain and to protect public health.