CHAPTER 33 



HAEMOPHILUS 



Definition. — Hcemophilus. 



Minute rods, sometimes almost coccal, sometimes thread-like ; may be highly 

 pleomorphic. Usually non-motile. Non-sporing, Gram-negative, non-acid-fast. 

 On first isolation dependent for growth on some factor, or factors, contained in blood 

 or in plant tissues. Some species retain this dependence after prolonged cultivation 

 on laboratory media. Some species are obligatory aerobes, or grow very poorly 

 under anaerobic conditions. All known species appear to be obligatory parasites, 

 inhabiting particularly the upper respiratory tract ; and most of the described 

 species or types are pathogenic. 



Type species. H. injluenzce. 



Since the isolation and description by Pfeiffer (1892, 1893) of the bacillus which, 

 though not the primary causal organism of influenza, is closely associated with that 

 disease, several other small, Gram-negative bacilli have been described, which share 

 with it certain characteristic growth requirements. In their final report on 

 classification and nomenclature, the American Committee (see Winslow .et al. 

 1920) grouped these species together under the generic name of Hcemophilus. The 

 generic definition suggested in the Committee's report opens the door more widely 

 than insistence on a close similarity in behaviour to the type species would allow ; 

 and such species as the Bordet-Gengou bacillus of whooping cough, the Morax- 

 Axenfeld bacillus of angular conjunctivitis, and Ducrey's bacillus of soft sore, have 

 been included, by certain writers, within this generic group. Such an extension of 

 the term " hsemophilic bacilli," whether in the form of a generic name or as a 

 convenient appellation for a characteristic bacterial group, has been opposed by 

 Kristensen (1922) and by Fildes (1923). It seems clear that their objection is valid 

 if the character from which the name is derived is to retain a decisive differential 

 significance. To include all the species referred to, it would be necessary to define 

 the genus on some other basis, with a sub-group characterized by the particular 

 growth requirements that H. influenzcB displays. There is no reason why we 

 should not do this. 



The two most important growth factors in blood which determine the haemo- 

 philic nature of Pfeiffer's bacillus have been identified, the one as a co-enzyme, 

 the other as an iron-containing pigment which presumably supplies the tetra- 

 pyrrole compounds necessary for the synthesis of cytochrome and related sub- 

 stances (see Chapter 3). But if we confine the term hsemophilic bacilli to strains 

 that need one or both of these substances for growth, we may be excluding organisms 

 which can synthesize the growth factors, but which are nevertheless closely related. 

 Moreover, the existence of organisms which synthesize small, sub-optimal amounts 

 of these growth factors provides a link between the definitely hsemophilic bacilli 



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