Haemolytic bacteria associated with life stages of the stable fly, Stomoxys calcitrans: Isolation and characterisation

Stable flies, Stomoxys calcitrans (Linnaeus, 1758), are widely recognised as significant blood-sucking insects that impact livestock and wildlife, leading to considerable economic challenges. Given their blood-feeding habits, our research focused on identifying the haemolytic gut bacteria in adults and exploring their life cycle stages. An investigation was carried out to isolate, characterise and identify culturable haemolytic bacteria associated with various life stages (eggs, larval instars, pupae and emerged adults), as well as with blood-engorged and non-engorged field-collected adult flies. The identification process employed a range of methods, including phenotypic traits, biochemical characteristics and antibiotic sensitivity tests of the isolated bacteria, along with Sanger sequencing of their 16S rRNA gene. Eleven bacterial strains were retrieved under the genera Bacillus and Lysinibacillus, with B. cereus being particularly abundant, represented by five distinct strains: SFB3, SFB4, SCE3, SC2L3, SMN5. Noteworthy is the presence of six bacterial strains, including four strains of B. cereus (SFB3, SCE3, SC2L3, SMN5) and two strains of L. macroides (SCE1, SC1L4), which were identified across different life stages and in field-collected adults. Among the isolated strains, six exhibited beta haemolysis, while the remaining five showed gamma haemolysis. These findings represent a valuable contribution to the understanding of the culturable haemolytic bacteria associated with the immature and adult stages of S. calcitrans. Furthermore, the identified bacteria may play a role in the digestion of the blood meal. This discovery warrants further investigation into the potential utility of these bacteria to mitigate the effects of stable flies on livestock and wildlife.