Functional Characterizations of Effector Protein BipC, a Type III Secretion System Protein, in Burkholderia pseudomallei Pathogenesis

Abstract

The results suggested that BipC possesses virulence determinants that play significant roles in host cell invasion and immune evasion.

Immune Recognition of the Epidemic Cystic Fibrosis Pathogen Burkholderia dolosa

“…B. dolosa AU0158 has a MIC of Ͻ64 g/ml for both ceftazidime and kanamycin (100; data not shown), and thus, the concentrations used in these experiments are also 15-fold higher than the MICs for this strain. The antibiotic concentrations of ceftazidime (for BCC) and kanamycin (for B. pseudomallei) used in this study are higher than what is routinely used in internalization/invasion assays (7,(101)(102)(103)(104)(105)(106)(107)(108)(109)(110)(111)(112), although we note that amikacin is usually used in conjunction with ceftazidime for BCC invasion assays but is the less effective of the two antibiotics for B. cenocepacia, B. multivorans, and B. dolosa (100). Levels of killing for all strains used in this experiment were greater than 99% under these conditions.…”

Characterization of the role of the Burkholderia pseudomallei type 3 secretion system using in vivo imaging.

“…Consequently, inactivation of bipD renders the bacterium incapable of efficient escape from endocytic vesicles, impaired intracellular replication and decreased intracellular survival in cultured macrophages, consistent with the phenotypes observed for bipB and bipC mutants, which make up the translocon pore [50,51]. Crystal structures of BipD and its Shigella homologue IpaD, suggest that BipD may play a role as an extracellular chaperone, by guiding and mediating the insertion of BipB and BipC into the host cell membrane and by potentially tethering the translocon pore to the T3SS needle [51].…”

“…Lastly, both bipB and bipC mutants are significantly attenuated in an intranasal BALB/c model of respiratory melioidosis, validating the requirement for formation of a translocon pore for full B. pseudomallei virulence in mammals [49,50]. Thus taken together, these data suggest that efficient formation of a translocon pore by B. pseudomallei T3SS3 translocon proteins is required for adherence, invasion, translocation of effectors and overall fitness of B. pseudomallei in mammalian infection.…”

“…BipB and BipC form a pore in the eukaryotic host cell membrane, but are also secreted into the cytoplasm; therefore it is possible that these translocon proteins may have additional roles during B. pseudomallei infection [44]. Accordingly, bipB and bipC mutants exhibit impaired invasion of nonphagocytic cultured cells and reduced intracellular fitness, strongly suggesting that efficient interaction of B. pseudomallei with host cells and efficient delivery of T3SS3 effectors to the cytoplasm of the cell is required for full virulence of the bacterium [49,50]. Notably, inactivation of bipC also leads to delayed escape of B. pseudomallei from endocytic vacuoles, leading to a 2-fold reduction in intracellular burden in cultured cells [50].…”

“…Accordingly, bipB and bipC mutants exhibit impaired invasion of nonphagocytic cultured cells and reduced intracellular fitness, strongly suggesting that efficient interaction of B. pseudomallei with host cells and efficient delivery of T3SS3 effectors to the cytoplasm of the cell is required for full virulence of the bacterium [49,50]. Notably, inactivation of bipC also leads to delayed escape of B. pseudomallei from endocytic vacuoles, leading to a 2-fold reduction in intracellular burden in cultured cells [50]. It is possible that inactivation of bipB leads to a similar phenotype, given that defective formation of a translocon pore likely leads to inefficient effector delivery, compromising the fitness of the bacterium in host cells.…”