TITLE:
Bacteroides fragilis Supernatant Extracts Enriched in Phenylacetic Acid Induce a Cytotoxic Effect in Mammalian Cells
AUTHORS:
Laís S. Falcão, Eduardo N. F. Antunes, Eliane O. Ferreira, Heidi Pauer, Maria Teresa V. Romanos, Rossiane C. Vommaro, Sérgio H. Seabra, Daniela S. Alviano, Celuta S. Alviano, Antonio Jorge R. da Silva, Leandro A. Lobo, Regina Maria C. P. Domingues
KEYWORDS:
Bacteroides fragilis, Vacuolization, Apoptosis, Vero cells Lineage, Peritoneal Macrophages, Phenylacetic Acid
JOURNAL NAME:
Advances in Microbiology,
Vol.5 No.10,
September
30,
2015
ABSTRACT: Bacteroides species are nearly half
of the fecal flora community and some are host symbionts crucial to host
nutrition and systemic immunity. Among Bacteroides species B. fragilis strains are
considered to be the opportunistic ones, being the most isolated anaerobic
bacteria in clinical samples. Cell-free supernatants of 65 B. fragilis strains were assayed and they were capable of inducing
vacuolating phenotype on Vero cells lineage. The supernatant of the Bacteroides fragilis ATCC 23745 strain was
elicited to have the strongest vacuolating effect on Vero cells monolayers and
peritoneal macrophages. Some drastic cell alterations were observed, such as a
general disorganization of cytoplasm and chromatin condensation, evidencing
cell death. By transmission electron microscopy it was confirmed that the
vacuoles observed were, in fact, swollen mitochondria. An immunocytochemical
assay, TUNEL, was used to confirm this hypothesis and showed that Vero cells
and peritoneal macrophages were dying by apoptotic process after exposition of B. fragilis cell-free supernatant.
Physical analysis of the apoptotic factor has revealed properties similar to
short-chain fatty acids. After gas chromatography and mass spectrometry
analysis, phenylacetic acid (PA) was characterized as the major compound
present in the most purified active fraction. We believe that the PA is
responsible for the pro-apoptotic effect elicited by the supernatant of B. fragilis cultures.