(see also Physiology of Bacteria section)

Table of contents :

  • Gram positive Bacteria
  • Gram negative Bacteria
  • Bibliography
  • Web resources

  • Thousands of different commensal microbial species populate Homo sapiens outer and inner body surfaces :

    Strictly anaerobs are always more represented (90 % in saliva, 98÷99 % in stools (Bacteroides:Escherichia 20:1), > 50 % in vagina) than strictly aerobs and facultative anaerobs taken together.
    Diverse methylotrophic bacteria were isolated from the tongue, and supra- and subgingival plaque in the mouths of volunteers and patients with periodontitis. One-carbon compounds such as dimethylsulfide in the mouth are likely to be used as growth substrates for these organisms. Methylotrophic strains of Bacillus, Brevibacterium casei, Hyphomicrobium sulfonivorans, Methylobacterium, Micrococcus luteus and Variovorax paradoxus were characterized physiologically and by their 16S rRNA gene sequences. The type strain of B. casei was shown to be methylotrophic. Enzymes of methylotrophic metabolism were characterized in some strains, and activities consistent with growth using known pathways of C1-compound metabolism demonstrated. Genomic DNA from 18 tongue and dental plaque samples of 9 volunteers was amplified by the PCR using primers for the 16S rRNA gene of Methylobacterium and the mxaF gene of methanol dehydrogenase. MxaF was detected in all 9 volunteers, and Methylobacterium was detected in 7. Methylotrophic activity is thus a feature of the oral bacterial community, low levels of which can be associated with bas oral smellref. The foot is also a source of methylated sulphides and strains of these odour eating bacteria, including Brevibacterium and Methylobacterium, which are also part of the normal foot microbial flora.

    Taxonomic units

    Gram-positive Bacteria
  • Firmicutes
  • => bacteremia
    Gram-negative Bacteria
    They all produce endotoxin orLPS : usually it is released in the medium during the post-logarithmic phase of growth or after bacterial cell lysis (only Pseudomonas aeuruginosa and Neisseria meningitidis release it by blebs) In vivo it is carried in plasma by HDL, LDL and LPS-binding protein (LBP): in the latter case LPS-LBP complex may bind CD14. When injected twice, it produces the Shwartzman reaction : Binding of LPS to CD14 and LBP is impaired by oxidized phospholipids (e.g. 1-palmitoyl-2-(5'oxovaleroyl) phosphatidylcholine (POVPC)). LPS resists autoclaving and cannot be converted into anatoxin by formaldehyde.
    N-terminal loops of OmpA, which is a 35-kDa highly conserved protein among Gram-negative Bacteria, bind to CCP3 of the a-chain of C4BP, which leads to a decrease in serum killing, allowing a certain threshold of bacteraemia
  • Bacteroidetes
  • Chlamydiae
  • Cyanobacteria
  • Fusobacteria
  • Proteobacteria (purple Bacteria and relatives)