Brucellae develop a persistent infection dependent on an effective early immune-recognition evasion

Larvae (n = 5) were inoculated with 106 Colony Forming Units (CFU)/larva of B. abortus 2308W (B. abortus 2308W mutant lacking a functional perosamine-synthase gene; the per gene is involved in the synthesis of the O-polysaccharide of the LPS) and B. microti CCM4915 (B. microti CCM4915 wild-type strain) (A) (left panel), and BaΔvirB (B. abortus 2308W mutant lacking a functional VirB system, non-polar mutant in virB10) and BaΔper (B. abortus 2308W mutant lacking a functional perosamine-synthase gene; the per gene is involved in the synthesis of the O-polysaccharide of the Lipopolysaccharide, LPS). (B). Larvae were homogenised at given time-points and bacterial load assessed by CFU counting. Results are expressed as mean ± standard deviation and differences between values of each sample versus B. abortus 2308W were considered significant at p < 0.05 (*), p < 0.005 (**) and p < 0.0005 (***). (C) Primary isolated G. mellonella haemocytes were infected with B. abortus 2308W-GFP (Brucella abortus 2308 virulent biovar 1 expressing Green Fluorescent Protein, GFP; the features of B. abortus 2308 are smooth LPS, spontaneous nalidixic acid resistance, virulence in mice) and BaΔvirB-GFP (B. abortus 2308W mutant lacking a functional VirB and expressing GFP), and intracellular bacterial load was screened at 2 and 48 h after infection.