Chemiluminescence of human leukocytes by black‐pigmented Bacteroides strains from dental plaque and other sites

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Abstract
The luminol‐dependent chemiluminescence (CL) of human leukocytes was determined after stimulation with different black‐pigmented Bacteroides strains, which had been isolated from plaque associated with periodontal disease and from clinical infections. In the presence of pooled human serum, variation was found in the CL caused by different black‐pigmented Bacteroides strains. The lowest CL was observed for B. gingivalis strains HG 66 and HG 76, which were the most virulent strains in an experimental animal model. Some strains of B. asaccharolyticus and B. corporis also caused a relatively low CL. To retain optimal CL, opsonization was necessary. Heating of the serum for 60 min at 56°C, to inactivate the complement, reduced the CL and the omission of serum even caused a lower CL. In the absence of serum B. gingivalis strains HG 66 and HG 76 and B. loescheii strain HG 64 caused a very low CL, whereas other strains of B. gingivalis still caused considerable CL.The agglutinating antibody titres in the pooled serum against the bacteria used in this study varied between 0 and 32. These differences in antibody litre could have influenced the results of the CL experiments. CL was not inhibited by washed bacterial suspensions.The hydrophobicity of black‐pigmented Bacteroides strains showed a great variation in hydrophobicity, when measured by the partition of the bacteria in a xylene/water two‐phase system. In the absence of serum, bacteria which were more hydrophilic proved to cause less CL. This suggested that a hydrophilic capsule of the bacteria could cause a low hydrophobicity and CL.