The pathogenicity of the predominantly non-capsulated, V-factor requiring haemophili that are commonly recovered from oral
infections has been explored by studies of their
endotoxins and infectivity as compared with those of Haemophilus influenzae. Similar yields of
endotoxin (2.40-2.59% w/w) were obtained from all the haemophili examined except H. haemolyticus (1.61% w/w). The
lipopolysaccharide (LPS) extracts all contained
heptoses but not
2-keto-3-deoxyoctonate (KDO). The
fatty acid compositions of the
lipid-A fractions were essentially similar but comprised 76% of the LPS in the H. influenzae type d strain tested and only 20% in the H. influenzae type b strain and some strains of H. parainfluenzae. All extracts contained
arachidic acid, which may be unique to haemophili. The
endotoxins from all strains produced characteristic pyrogenic and polymorph effects in rabbits. The
endotoxins from the pharyngeal X- and V-factor-requiring strains had LD50 values for
actinomycin-D-sensitised mice of 2.4-2.7 micrograms/kg, and were about eight times more potent than those from the oral V-factor-requiring strains (LD50 values 17.2-22.4 micrograms/ml). Approximately ten thousand times more free
endotoxin was detected in broth cultures of H. influenzae type b than in those of oral haemophili, and this greater
endotoxin release was not associated with a greater degree of
autolysis.
Endotoxin release from viable cells may be important in the pathogenicity of this organism. H. influenzae type b was much more potent in producing
infection in chambers implanted subcutaneously in guinea pigs than were oral strains of haemophili; only 10 type b organisms were required, compared with 9 X 10(5) of H. parainfluenzae. However, in
infections maintained for 90 days, the numbers of haemophili--c. 10(7)/ml of chamber fluid--were similar for all the test strains. Thus, although the oral haemophili lack special attributes of invasiveness and resistance to host defences, they are not devoid of pathogenic potential and, if allowed to proliferate, may become an important
element in an
infection.