Assessment of pathogenic bacterial loads in black soldier fly larvae (hermetia illucens) reared on food waste substrates.
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Date
2026
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Busitema University
Abstract
The bioconversion of organic wastes using Black soldier fly larvae (Hermetia illucens) is an emerging sustainable feed solution in Uganda, yet it presents significant microbial safety challenges. This study evaluated bacterial safety and pathogen diversity in BSFL and resulting frass when reared on local organic wastes. Larvae were reared feed formulation of 5 kg brewer's waste + 1 kg maize bran + 2 kg hotel waste with 2 kg larvae per bin. Microbial bioburdens specifically Total Aerobic Bacterial Counts (TABC), coliforms/Escherichia coli, presumptive Salmonella/Shigella spp., and Staphylococcus spp. were quantified using culture-dependent techniques and biochemical profiling. Sampling spanned six distinct matrices: raw substrate, live 5th instar larvae, non-feeding prepupae, blanched larvae (100°C for 15 minutes), thermally dehydrated larvae (70°C for 1 hour), and raw versus heated frass. Raw substrates harbored high baseline bacterial loads (> 8.9 Log10 CFU/g), which directly colonized the un-processed live larvae (9.40 Log10 CFU/g). Natural gut evacuation during the prepupal stage failed to significantly reduce this bioburden (9.29 Log10 CFU/g, p = 0.983). While Gram-negative enteropathogens and spore-forming Bacillus spp. persisted throughout the life cycle and processing stages, Staphylococcus aureus was uniquely suppressed post-ingestion, suggesting effective competitive exclusion and antimicrobial peptide activity within the larval gut. Mild post-harvest thermal processing (short blanching and oven drying) yielded statistically significant microbial reductions; however, residual total viable counts (8.91 Log10 CFU/g) and presumptive Salmonella spp levels (> 6.8 Log10 CFU/g) remained critically above the UNBS and EU maximum limits (≤ 5.0 Log10 CFU/g and zero tolerance in 25 g, respectively). Pathogen loads in BSFL strongly correlated with the initial bioburden of their organic rearing media. The standalone mild thermal kill-steps currently utilized by smallholder farmers are insufficient to guarantee microbiological safety. To mitigate zoonotic transmission risks and achieve market compliance, the adoption of rigorous, multi-stage thermal processing protocols and substrate pre-treatment is essential.
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Undergraduate research report
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Icariat, E. P. (2026). Assessment of pathogenic bacterial loads in black soldier fly larvae (hermetia illucens) reared on food waste substrates. [Unpublished undergraduate research report]. Busitema University.