Neutrophils play a key role in the control of Burkholderia pseudomallei, the pathogen that causes melioidosis. Here, we show that survival of intracellular B. pseudomallei was significantly increased in the presence of 3-methyladenine or lysosomal cathepsin inhibitors. The LC3-flux was increased in B. pseudomallei-infected neutrophils. Concordant with this result, confocal microscopy analyses using anti-LC3 antibodies revealed that B. pseudomallei-containing phagosomes partially overlapped with LC3-positive signal at 3 and 6 h postinfection. Electron microscopic analyses of B. pseudomallei-infected neutrophils at 3 h revealed B. pseudomallei-containing phagosomes that occasionally fused with phagophores or autophagosomes. Following infection with a B. pseudomallei mutant lacking the Burkholderia secretion apparatus Bsa Type III secretion system, neither this characteristic structure nor bacterial escape into the cytosol were observed. These findings indicate that human neutrophils are able to recruit autophagic machinery adjacent to B. pseudomallei-containing phagosomes in a Type III secretion system-dependent manner.
Keywords: 3MA, methyladenine; Bp, Burkholderia pseudomallei; Bsa, Burkholderia secretion apparatus; Burkholderia pseudomallei; KM, kanamycin; LAMP1, lysosomal-associated membrane protein 1; LC3-I, unlipidated form of LC3; LC3-II; LC3-II, LC3-phospholipid conjugated and phagophore or autophagosome-associated form of LC3; MAP1LC3/LC3, microtubule-associated protein 1 light chain 3; MOI, multiplicity of infection; NET, Neutrophil Extracellular Taps; T3SS; T3SS, Type III secretion system; WT, wild type; autophagy; melioidosis; neutrophils; p.i., postinfection.