Prevalence and associated risk factors for Salmonella enterica contamination of cow milk and cottage cheese in Ethiopia

Abstract

Animal sourced foods, such as dairy products, are common sources of Salmonella enterica, a foodborne pathogen of increasing global concern, particularly in developing countries. In Ethiopia, most data on the prevalence of Salmonella in dairy products is highly varied and limited to a specific region or district. Furthermore, there is no data available on the risk factors for Salmonella contamination of cow milk and cottage cheese in Ethiopia. This study was therefore conducted to determine the presence of Salmonella throughout the Ethiopian dairy value chain and to identify risk factors for contamination with Salmonella. The study was carried out in three regions of Ethiopia, including Oromia, Southern Nations, Nationalities and Peoples, and Amhara during a dry season. A total 912 samples were collected from milk producers, collectors, processors, and retailers. Samples were tested for Salmonella using the ISO 6579-1: 2008 method, followed by PCR confirmation. Concurrent with sample collection, a survey was administered to study participants to identify risk factors associated with Salmonella contamination. Salmonella contamination was highest in raw milk samples at the production (19.7%) and at milk collection (21.3%) levels. No significant difference in the prevalence of Salmonella contamination among regions was detected (p > 0.05). Regional differences were apparent for cottage cheese, with the highest prevalence being in Oromia (6.3%). Identified risk factors included the temperature of water used for cow udder washing, the practice of mixing milk lots, the type of milk container, use of refrigeration, and milk filtration. These identified factors can be leveraged to develop targeted intervention strategies aimed at reducing the prevalence of Salmonella in milk and cottage cheese in Ethiopia.

Seasonal variation of Salmonella enterica prevalence in milk and cottage cheese along the dairy value chain in three regions of Ethiopia

“…Second, the selected study locations had a complete set of value chain actors, including producers, collectors, processors, and retailers. Due to the region’s recent reorganization, the SNNP region that was referenced in our previous report (Bedassa et al 2023 ) was now the Sidama region.…”

“…In the wet season (June, July, and August), a total of 228 cow milk and cottage cheese samples (92 raw milk, 92 pasteurized milks, and 44 cottage cheese) were collected from Debre Zeit ( n = 120), Hawassa ( n = 60), and Bahir Dar ( n = 48). Previously published data from the dry season was used for the seasonal comparison (Bedassa et al 2023 ). The dry season samples were collected from the same producers, collectors, processors, and retailers as during wet season (January, February, March, and April).…”

“…Figure 1 illustrates Salmonella enrichment and isolation according to ISO 6579-1: (ISO 2017 ). The full detailed procedure of Salmonella enrichment and isolation were outlined in our prior report (Bedassa et al 2023 ). Buffered Peptone Water (BPW) (Oxoid, CM 0509) was used for the pre-enrichment of Salmonella, and it was incubated for 18 h at 35 °C.…”

“…Salmonella isolates were confirmed utilizing PCR targeting the invA gene (Galán and Curtiss III, 1991 ). The full and detailed procedure of Salmonella PCR conformation was outlined in our prior report (Bedassa et al 2023 ). Each electrophoresis run included a 100 bp DNA ladder, as well as positive ( Salmonella enterica ATTCC 35,664) and negative controls (nuclease free water).…”

“…The relationship between temperature and precipitation and the frequency of salmonellosis cases is supported in multiple scientific publications (Rose et al 2001 ; Zhang et al 2010 ; Putturu et al 2015 ; Stephen and Barnett 2016 ; Park et al 2018 ; Judd et al 2019 ; Ung et al 2019 ). Recently, Bedassa et al ( 2023 ) reported a 13.8% prevalence of the organism in milk and cheese in samples collected from the Oromia, Sidama, and Amhara regions of the country in the dry season. Studies on seasonal variations and regional distributions of pathogenic organisms are crucial for developing strategic interventions and anticipating outbreaks.…”