Beschreibung:
<jats:p>
Previous investigators have suggested that opsonization of two
<jats:italic>Bacteroides</jats:italic>
species is mediated exclusively by the alternative complement pathway and requires immunoglobulins. In this study, the nature of the opsonic factors in nonimmune human serum for four species of
<jats:italic>Bacteroides</jats:italic>
was investigated by measuring uptake of [
<jats:sup>3</jats:sup>
H]thymidine-labeled bacteria by human polymorphonuclear leukocytes. Normal human serum, C2-deficient serum, immunoglobulin-deficient serum, and serum chelated with ethylene glycol-bis(β-aminoethyl ether)-
<jats:italic>N</jats:italic>
,
<jats:italic>N</jats:italic>
-tetraacetic acid (EGTA), MgEGTA, and ethylenediaminetetraacetic acid (EDTA) were used as opsonic sources. Heat inactivation of each of these sera significantly reduced its opsonic activity for all four
<jats:italic>Bacteroides</jats:italic>
species, suggesting that serum complement was essential for effective opsonization. All strains were opsonized in the absence of the classical complement pathway; however, kinetics studies revealed that opsonization proceeded at a significantly faster rate when the classical complement pathway was intact. Although two strains were opsonized in immunoglobulin-deficient sera, opsonization was less efficient and appeared to occur via the alternative complement pathway. Unexpectedly, all strains were well opsonized by the classical complement pathway in 10% serum which had been effectively chelated with EGTA or EDTA. The explanation for this finding is unknown; however, it is possible that cell wall cations of
<jats:italic>Bacteroides</jats:italic>
species may participate in the activation of complement in chelated serum, resulting in effective opsonization. It was also found that
<jats:italic>Bacteroides</jats:italic>
, when incubated with an
<jats:italic>Escherichia coli</jats:italic>
strain in normal serum, could compete for opsonins and thereby reduce phagocytosis of
<jats:italic>E. coli.</jats:italic>
It is possible that competition for opsonins among bacterial species contributes to the synergistic role these organisms share in mixed floral infections.
</jats:p>