Aggregatibacter (Actinobacillus) actinomycetemcomitans
Cultural characteristics
Biochemical characters
Phylum Proteobacteria, Class Gammaproteobacteria, Order Pasteurellales, Family Pasteurellaceae, Genus Aggregatibacter,  
Aggregatibacter actinomycetemcomitans
(Klinger 1912; Topley and Wilson 1936) Nørskov-Lauritsen and Kilian 2006.
Actinobacillus actinomycetemcomitans (Klinger 1912) Topley and Wilson 1936.
Old synonyms:
Bacterium actinomycetemcomitans Klinger 1912, Haemophilus actinomycetemcomitans (Klinger 1912) Potts et al.
Cocci, 0.6-0.8 x 0.6- 1.4 µm, or rod-shaped cells (in agar cultures); may occur singly,
in pairs or in small clumps. Nonmotile. Cells have a microcapsule.
Colonies are 0.5-3 mm in diameter, adhere to the agar medium and are described as
starlike or “crossed cigars”. Colonies may sometimes have a rough surface and they
become mucoid and non-adherent after repeated subculture.
Growth in broth in the form of granules at the bottom and up the sides of the tube (“tiny
colonies”), while subsequent cultures become less adherent and exhibit uniform
Grows poorly in air but well in 5% CO
2 or under anaerobic conditions. Optimum
growth at 37 ºC, no growth at 22 ºC.
Growth on MacConkey agar is negative. No hemolysis on sheep blood agar. V-factor
and X-factor independent.
Indigenous to humans, with primary habitat on dental surfaces.
Implicated in the etiology of destructive periodontal diseases; it has also been isolated from abcesses (abdominal, brain, facial,
hand, mediastinal and thyroid) and from cases of actinomycosis, endarteritis, endocarditis, meningitis, pneumonia, septicemia,
urinary tract infections and vertebral osteomyelitis.
Potential virulence factors:
- leucotoxin (a 116-kDa protein),
- fimbriae (a 52-54-kDa subunit protein),
- a cytolethal distending toxin,
- enzymes that are able to degrade immunoglobulins G, M, A,
- cell-associated and extracellular components that are able to bind the Fc region of immunoglobulin molecules (a 25-32-kDa
outer-membrane protein,
- collagenases,
- proteases.
  1. Olsen I., Moller K., 2004. Genus II. Actinobacillus. In: Bergey’s Manual of Systematic Bacteriology, Second edition, Vol two, part B,
    George M. Garrity (Editor-in-Chief), pp. 866-883.
  2. W.M. Janda, R. Mutters, 2006. Pasteurella, Mannheimia, Actinobacillus, Eikenella, Kingella, Capnocytophaga, and other
    miscellaneous Gram-negative rods. In: Topley & Wilson’s Microbiology and Microbial Infections, 10 edition, Vol. 2, Bacteriology,
    Edward Arnold Ltd.
  3. J. G. Holt et al., 1994. Facultatively Anaerobic Gram-Negative Rods. Subgroup 3. Family Pasteurellaceae. In: Begey’s Manual of
    Determinative Bacteriology, 9th-edition, Williams & Wilkins, pp 194-196.
  4. Buchanan R.E., Gibbons N.E. (co-editors), 1975. Bergey’s  Manual of Determinative Bacteriology, eight edition, The Williams &
    Wilkins Company, Baltimore.
  5. N. Norskov-Lauritsen and M. Kilian, 2006. Reclassification of Actinobacillus actinomycetemcomitans, Haemophilus aphrophilus,
    Haemophilus paraphrophilus and Haemophilus segnis as Aggregatibacter actinomycetemcomitans gen.nov., comb. nov.,
    Aggregatibacter aphrophilus comb. nov.and Aggregatibacter segnis comb. nov., and emended description of Aggregatibacter
    aphrophilus to include V factor-dependent and V factor-independent isolates.IJSEM, 56, 2135-2146.
Positive results for nitrates reduction, oxidase, alkaline phosphatase, catalase, acid production from: D(+) glucose, D(+) mannose,
maltose & D(-) fructose.

Negative results for gelatinase, H
2S, urease, arginine dehydrolase, lysine decarboxylase, ornithine decarboxylase, indole, ONPG, gas
production from D(+) glucose, acid production from: glycerol, L(+) arabinose, dulcitol, L(+) rhamnose, meso-inositol, D(-) sorbitol,
cellobiose, lactose, melibiose, sucrose (saccharose), trehalose, raffinose, inulin, esculin & salicin.

Variable results for acid production from: D(+) xylose, mannitol, D(+) galactose & dextrin.
(c) Costin Stoica
Culture media
Biochemical tests
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