The role of Staphylococcus agnetis and Staphylococcus hyicus in the pathogenesis of buffalo fly skin lesions in cattle

Buffalo flies (Haematobia irritans exigua) are hematophagous ectoparasites of cattle causing production and welfare impacts in northern Australian herds. Skin lesions associated with buffalo fly infestation and Stephanofilaria nematode infection are manifested as focal dermatitis or ulcerated areas most commonly on the medial canthus of the eye, along the lateral and ventral neck and on the abdomen of cattle. For closely related horn flies (Haematobia irritans irritans), Staphylococcus aureus have been suggested as a contributing factor in the development of lesions. To investigate the potential role of bacterial infection in the pathogenesis of buffalo fly lesions, swabs were taken from lesions and normal skin, and bacteria were also isolated from surface washings of buffalo flies and surface-sterilised homogenized flies. Bacterial identification was conducted by MALDI-TOF, strain typing by rep-PCR and DNA sequencing to determine species similarity and virulence factors. Of 49 bacterial isolates collected from lesions, 37 were identified as Staphylococcus agnetis and 12 as Staphylococcus hyicus, whereas from normal skin four isolates were S. hyicus and one was Staphylococcus sciuri. Of the Staphylococcus isolates isolated from buffalo flies, five were identified as S. agnetis and three as S. hyicus. Fifty percent of the buffalo fly isolates had rep-PCR genotypic patterns identical to the lesion isolates. Genome sequencing of 16 S. agnetis and four S. hyicus isolates revealed closely similar virulence factor profiles, with all isolates possessing exfoliative toxin A and C genes. The findings from this study suggest the involvement of S. agnetis and S. hyicus in buffalo fly lesion pathogenesis. This should be taken into account in the development of effective treatment and control strategies for lesions.