806 HEMOPHILUS 



We have, as yet, no evidence with regard to variation in the other species of this 

 group. 



H. influenzae 



Isolatinn.- — Isolated by PfeifFer (1892) from cases of influenza in man. 



Habitat. — Strict parasite, living particularly in the upper respiratory tract of man. 



Morphology. — In its typical form H. influenzce is a tiny cocco-bacillus (1-1-5 by 0-3-0-4^). 

 According to Pittman (1931), the bacillus in its virulent smooth form is capsulated. 

 Most strains, even when first isolated from the tissues are non- capsulated, but it 

 is possible that these should be regarded as rough variants. Among any large sample 

 of strains, or in any one strain during prolonged subculture in the laboratory, 

 wide departures from the typical morphology will usually be found. Longer bacillary 

 forms and definitely filamentous forms often occur, and the latter may show angular 

 bendings or sinuous curves. In the filamentous forms globular or ovoid swellings 

 are not uncommon. The organism is non-flagellated, and forms no spores. It 

 stains feebly with many of the ordinary bacteriological dyes, more readily with 

 dilute carbol-fuchsin. It is Gram-negative and not acid-fast. 



Growth requirements. — H. influenzce requires both the X factor and V factor for its growth. 

 It grows far more readily under aerobic than imder anaerobic conditions, and it 

 would appear that some strains are incapable of prolonged anaerobic subcultivation. 

 The optimal temperature for growth is in the neighbourhood of 37° C. 



Growth on Solid Media.- — On Fildes' or Levinthal's medium the usual type of colony 

 produced by H. influenzce is transparent, or shghtly opaque, circular and dome- 

 shaped, or shghtly conical, with a slightly splayed-out entire edge. At the end 

 of 24 hours' growth at 37° C. these colonies usually attain a diameter of 0-5-0-8 mm. 

 On further incubation, and in some cases during the first 24 hours, the colony becomes 

 differentiated into a central portion with a granular or contoured surface, an inter- 

 mediate flattened portion, and a sharply bevelled periphery with a narrow splayed- 

 out edge. During the second 24 hours of growth the colony usually enlarges to a 

 diameter of 1-1-5 mm. There is a tendency, which is not absolute, for differentia- 

 tion to occur earlier, and to be more pronounced, in strains that have an atypical 

 morphology. The growth is butyrous and emulsifies easily. 



Some strains, described by Pittman (1931) as smooth, and by Chandler, Fother- 

 giU and Dingle (1939) as mucoid, give colonies that differ from those described 

 above in having a smooth, undifferentiated, shghtly mucoid surface. They have 

 an entire edge. They tend to attain a larger size (1-3 mm. in diameter). They 

 are shghtly opaque ; and, when viewed by obhquely transmitted Ught, they are 

 iridescent Strains that give this type of colony show antigenic characters, and 

 differences in pathogenicity, which are in accord with the view that they represent 

 the " smooth " phase of the organism, while the more frequently encountered 

 strams, having the colonial appearances previously described, are in the non- 

 mucoid or the rough state, and are not iridescent. 



Growth in Liqtiid Media. — In a suitable Uquid medium most strains of H, influenzce give 

 rise to a uniform turbidity, with or without a shght powdery deposit. Some give 

 a more flocculent deposit. The latter usually show an atypical morphology, and 

 the colonial appearances associated with the more advanced stage of rough variation. 



Resistance. — H. influenzce is killed by an exposure to a temperature of 50-55° C. for 30 

 mmutes. 



Biochemical Activities. — H. influenzce usually ferments dextrose, though not vigorously, 

 producing acid without gas. Lactose and mannitol are never fermented. The 

 action on maltose, saccharose and dextrin varies. Smooth and morphologically 

 typical strains tend not to attack these substrates. The rougher, morphologically 

 atypical strains ferment them rather more frequently. The production of indole 

 shows a high correlation with other characters that differentiate between relatively 



