Insights into the microbiological safety of vermicompost and vermicompost tea produced by South African smallholder farmers

Abstract

Feedstock used in the production of vermicompost (VC) and vermicompost tea (VCT) may harbour various pathogenic bacteria responsible for a number of animal and human diseases worldwide. The identification and characterisation of such pathogenic organisms is necessary for assessing the safety of these products. In the present study, our goal was to determine the presence of possible pathogens in VC and VCT and, if present, to determine the antimicrobial susceptibility profiles of the organisms. VC and VCT samples were collected from five different farms in the Winterveldt, South Africa. Only one out of 60 VC and VCT samples was found to contain a potentially pathogenic organism. The use of phenotypic procedures aided the final identification of the isolate, which was confirmed to be Salmonella enterica serovar Typhimurium. This isolate tested positive for species specific invA genes. Antibiotic testing using the agar diffusion technique showed that the Salmonella isolate was resistant to only kanamycin. The Salmonella counts that were observed in this study were lower than the generally accepted infective doses of these bacteria. In the light of these findings, it was concluded that VC and VCT produced by the farmers involved presented a low risk in terms of the safety of the products