Surface receptors for human serum albumin in Peptococcus magnus strains

Eighty-one bacterial strains representing 16 anaerobic species were tested in a sensitive binding assay for uptake of 125I-labelled human serum proteins. Fifteen of 36 Peptococcus magnus strains (42%) bound significant amounts of human serum albumin (HSA). None of the other bacterial species showed any affinity for HSA. All strains studied were incapable of uptake of human fibrinogen, fibronectin, haptoglobin or aggregated beta 2-microglobulin. P. magnus strain Ra 4 was tested for binding of purified serum albumin from 11 animal species, and showed a binding profile similar to human group-C and -G streptococci, but different from Streptococcus pyogenes, Strep. zooepidemicus and Strep. dysgalactiae. Kinetic experiments showed that albumin binding was a rapid displaceable, time-dependent process, that could take place over a wide range of pH or salt concentrations. The albumin-binding component of P. magnus strain Ra 4 was resistant to heat and to periodate treatment, but sensitive to proteolytic enzymes.