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Bacterial flora in faecal samples from reared Jamaican field cricket (Gryllus assimilis)

Alternative feed sources are very popular subject of scientific studies. One of them is Jamaican field cricket (Gryllus assimilis), known for its high protein value, favorable fatty acid profile and amino acid composition. There are numerous advantages regarding use of insects as alternative feed source, however the regulations concerning health safety and hygienic quality are still not completely clear. As a part of our research on the potential of using insects as feed for poultry, we are investigating microbiological safety of crickets for feed and food. In this study, we wanted to explore which bacteria can be found as a part of the physiological microflora of intensively reared crickets, in what amount are those bacteria present and secondly, are some of the detected bacteria possibly harmful. Faecal samples from a cricket colony at two different ages were analyzed using standard microbiological procedures for the detection of aerobic bacteria. The procedures were done in duplicates. 1 g of faeces was thoroughly mixed in 10 ml of normal saline. Aliquot of 1 ml was transferred into the clean tube and diluted serially in one- tenth stepwise to 10^5 dilution. From the dilution of 10^5, 100 μl aliquot was transferred aseptically to the Brilliant Green Agar and UTI Brilliance Clarity Chromogenic Agar and spread evenly with a sterile loop. The inoculated plates were incubated aerobically at 37 ̊C over the night and afterwards the plates were examined for growth. The non-diluted samples were also plated in order to confirm if there were some pathogenic aerobic bacteria present in the samples in smaller amounts. The identification of the bacteria was done based on morphological characteristics of the colonies and microscopically via Gram staining in addition to biochemical testing. Confirmation of the identification was done using matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) method.The Brilliant Green Agar plates were negative, as opposed to UTI Brilliance Clarity Chromogenic Agar on which we counted CFU. The microbial load for bacteria ranged from 143 x10to 208 x10CFU/g. The detected bacteria in the samples were Enterococcus thailandicus, Enterococcus raffinosus, Enteroccocus termitis, Acinetobacter baumannii, Acinetobacter guillouiae, Providencia rettgeri and Providencia alcalifaciens, out of which Providencia spp. were present in the largest amount (75- 96%). Additionaly, from the non-diluted samples Kosakonia cowanii, Klebsiella pneumoniae and Raoultella ornithinolyticawere detected in very small amounts. The samples were negative for salmonellae and E. coli. Although the potential of using insects as feed has been greatly explored, there are still no definite regulations regarding microbiological quality and safety. The detected bacteria can mostly be found in soil and water or as a part of normal microflora in insects. Some of the mentioned bacteria are opportunistic pathogens that could potentially be harmful to immunocompromised animals or people. Since there is no official data on the autochthonous microbiota in Gryllus assimilis, these results are valuable for further research on alternative feed sources.

Gryllus assimilis, Jamaican field cricket, alternative feed source, poultry feed

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