Coliform Contamination of Milk in Smallholder and Pastoral Dairy Value Chains in Kenya and its Implication on Post-Harvest Losses and Consumer Safety

Abstract

Coliforms are a marker of hygiene and indicators for pathogenic microbes in milk. Some strains are pathogenic and cause human and animal infections. Coliforms also contribute to milk spoilage by hydrolysing lactose. Their occurrence is mostly due to practices in handling milk along the value chain. The aim of this study was to assess the risk factors for occurrence of coliforms in milk along the dairy value chain in Kenya, their biochemical profiles, phylogenetic distribution, pathogenicity, and antibiotic sensitivity. Nakuru and Isiolo Counties represented Smallholder cow milk value chain and Pastoral camel milk value chain respectively. A cross sectional study was designed for data collection, and data was collected by observation, interviews, and focussed group discussions. In addition, laboratory analyses of milk samples, udder swabs, hand swabs, and water was also done. Quantitative data was analysed using SAS 9.4; and a phylogenetic tree was generated using MEGA version 7. The proportion of milk not meeting quality standards based on coliform counts was 50% for Smallholder rural, 66% for Smallholder peri-urban, and 40% for Pastoral value chains. Risk to high coliform counts was lack of training of milking persons on milk hygiene, use of unhygienic plastic containers and the length of time taken to deliver milk, at high ambient temperature, to secondary collection centres. Additionally, excessive human handling of milk at the pastoral secondary collection centres, and transporting the milk at ambient temperature for a long time was a risk to increased coliform counts for milk delivered to Nairobi market. The dominant coliforms constituting 58% of enterobacteriaceae were E. coli, E. cloacae, K. pneumoniae, and K. oxytoca. All E. coli isolates were positive for indole which is important in bacterial toxicity, drug defence, and biofilm adhesion. None of the isolates was positive for inositol, ruling out soil as source of the microbes. For K. pneumoniae, tests for Lysine decarboxylase in both camel milk isolates (80% +ve) and cow milk isolates (87.5% +ve) was similar to clinical isolates. All K. pneumoniae isolates from cow milk tested positive for citrate and urease indicating their role in pathogenicity. Phylogenetic distribution of the coliforms was random with regard to source and value chain. E. coli β-haemolytic isolates had a prevalence of 25% in cow milk and 33% in camel milk, and none isolated from the environment. Of the isolates, 12.5% and 19.0% for cow and camel milk respectively were multi-drug resistant to ampicillin, cefotaxime, and cefepime. To reduce Post-harvest losses and enhance food safety, the study recommends addressing the identified risks as well as enhancing antibiotic stewardship in animal disease management.