Aggregative adherent strains of Corynebacterium pseudodiphtheriticum enter and survive within HEp-2 epithelial cells

Corynebacterium pseudodiphtheriticum is a well-known human pathogen that mainly causes respiratory disease and is associated with high mortality in compromised hosts. Little is known about the virulence factors and pathogenesis of C. pseudodiphtheriticum. In this study, cultured human epithelial (HEp-2) cells were used to analyse the adherence pattern, internalisation and intracellular survival of the ATCC 10700 type strain and two additional clinical isolates. These microorganisms exhibited an aggregative adherence-like pattern to HEp-2 cells characterised by clumps of bacteria with a "stacked-brick" appearance. The differences in the ability of these microorganisms to invade and survive within HEp-2 cells and replicate in the extracellular environment up to 24 h post infection were evaluated. The fluorescent actin staining test demonstrated that actin polymerisation is involved in the internalisation of the C. pseudodiphtheriticum strains. The depolymerisation of microfilaments by cytochalasin E significantly reduced the internalisation of C. pseudodiphtheriticum by HEp-2 cells. Bacterial internalisation and cytoskeletal rearrangement seemed to be partially triggered by the activation of tyrosine kinase activity. Although C. pseudodiphtheriticum strains did not demonstrate an ability to replicate intracellularly, HEp-2 cells were unable to fully clear the pathogen within 24 h. These characteristics may explain how some C. pseudodiphtheriticum strains cause severe infection in human patients.

Facultative alkalophilic bacteria from mangrove soil with varying buffering capacity and H+ conductance.

Facultative alkalophilic bacteria Planococcus sp. (EMGA-26), Bacillus sp. (EMGA-29) and Corynebacterium spp. (EMGA-33 and 130) were isolated from mangrove soil samples. Neutrophiles were predominant than alkalophiles. Buffering capacity and membrane H+ conductance were investigated for the strains grown in PPYG medium at pH 10.5 using acid pulse technique. Bacillus sp. showed higher buffering capacity than Planococcus sp. and Corynebacterium spp. Buffering capacity was two-fold higher in Corynebacterium sp. EMGA-33 than in EMGA-130. The membrane H+ conductance was high in Bacillus sp. and was directly proportional to the buffering capacity values. The Bacillus sp. (EMGA-29) had higher cell membrane adaptability in high pH environment than the Planococcus sp. and Corynebacterium spp.