Microbial contaminants in wild harvested and traded edible long-horned grasshopper, Ruspolia differens (Orthoptera: Tettigoniidae) in Uganda

Abstract

Edible insects are now globally recognised as alternative sources of food and feed. Currently, over 470 spp of insects are consumed in Africa alone, with Ruspolia differens being the most common in central Uganda. Harvesting and trading of these insects is done informally and the post-harvest handling, processing and marketing involves several people. These coupled with other factors increase the risk of microbial contamination of R. differens. This study identified and characterised bacterial and fungal microbes found in R. differens along the value chain, and also evaluated the safety levels of R. differens at the different points, including their different districts of origin. Samples of whole R. differens were collected from wild vegetation, trapping sites and markets. Additionally, samples of plucked and deep-fried ready-to-eat R. differens were collected from the markets. The samples were cultured on standard media for microbial quantification, and pure cultures were identified and characterised using molecular techniques. There were seven species each of bacteria and fungi recorded in R. differens samples, with harvesting drums harbouring more microbes compared to the other points along the value chain. The key pathogenic bacteria detected in marketed R. differens were Staphylococcus sciuri, Acinetobacter baumannii and Serratia marcescens, all of which were absent in wild-caught whole R. differens. The bacterial and fungal counts in deep fried ready-to-eat R. differens were ~3- and 2-fold lower, respectively, than in raw samples, and the values in deep fried R. differens were within the recommended microbial limits for edible insects. In terms of bacterial loads, the most unsafe samples were the whole R. differens samples from the market followed by those from trapping points. The fungal counts in the raw R. differens were comparable across the sampling points, making their safety concerns comparable along the value chain. Districts of origin did not compromise the safety of R. differens sold in Kampala. These results demonstrate that R. differens obtained at the trapping sites and markets are contaminated with potentially harmful microbes, with varying levels of safety concerns. Processing through deep frying greatly minimises the health risks associated with consumption of R. differens through lowering the loads of microbial contaminants. However, the specific handling practices at distribution points, trapping points and markets (for ready-to-eat R. differens) which may be responsible for introducing microbes into R. differens still needs to be addressed.