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Infection and Immunity, August 2000, p. 4611-4615, Vol. 68, No. 8
Department of Molecular Cellular Oncology and
Microbiology1 and Department of
Periodontology,2 Graduate School, and
Instrumental Analysis Research Center for Life
Science,3 Tokyo Medical and Dental
University, 1-5-45, Yushima, Bunkyo-Ku, Tokyo 113-8549, Japan
Received 14 February 2000/Returned for modification 3 April
2000/Accepted 18 May 2000
Bacteroides forsythus, which has been reported to be
associated with periodontitis but has not been recognized as a key
pathogen, was found to induce cytolytic activity against HL-60 and
other human leukemic cells. This cytolytic activity was demonstrated according to three different criteria: (i) loss of both mitochondrial membrane potential and membrane integrity in cells treated with bacterial extracts and then with Rh123 and propidium iodide,
respectively, as demonstrated by flow cytometry; (ii) damage to
cytoplasmic membrane, as revealed by scanning electron microscopy
(SEM); and (iii) DNA ladder formation and activation of caspase-3.
These results indicate that B. forsythus produced an
apoptosis-inducing factor(s) found to be composed of
protein as judged by heat and trypsin sensitivity. In addition to
extracts from B. forsythus, the culture supernatant of this
bacterium has the ability to induce a cytolytic effect against
peripheral white blood cells, especially lymphocytes. For
comparison with B. forsythus, the same analyses were
applied to two strains with different serotypes of
Actinobacillus actinomycetemcomitans, serotypes a (ATCC
43717) and c (ATCC 43719), in addition to previously reported
apoptosis-inducing serotype b (ATCC 43718), which was used as a
positive control. The strains of A. actinomycetemcomitans
serotypes a and b induced apoptosis in HL-60 cells as judged by the
above three criteria but to a slightly lesser extent than did B. forsythus, while the serotype c strain produced apoptosis to a
negligible extent. Detailed SEM images showed that the A. actinomycetemcomitans serotype a strain induced large-pore
formation and the serotype b strain produced small pores with typical
blebbing, while B. forsythus induced severe membrane
ruffling. Further DNA ladder formation and caspase-3 activation were
observed in the serotype a and b strains but not in the serotype c
strain. The present paper is the first report of a protein
factor(s) from B. forsythus and the A. actinomycetemcomitans serotype a strain which induces
apoptotic cell death.
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Novel Apoptosis-Inducing Activity in
Bacteroides forsythus: a Comparative Study with Three
Serotypes of Actinobacillus actinomycetemcomitans
*
Corresponding author. Mailing address: Department of
Periodontology, Graduate School, Tokyo Medical and Dental University, 1-5-45, Yushima, Bunkyo-Ku, Tokyo 113-8549, Japan. Phone:
81-3-5803-5456. Fax: 81-3-5803-0189. E-mail:
shinichi.peri{at}dent.tmd.ac.jp.
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