490 PFEIFFERELLA, AND CERTAIN ALLIED ORGANISMS 



Classification. — There are many points of resemblance between Pf. mallei and 

 the organisms of the Brucella group. Both this organism and Br. melitensis are 

 small, non-motile, Gram-negative bacilli, developing slowly in culture media ; both 

 give rise to a cafe-au-lait or chocolate-coloured growth on potato ; both have very 

 weak fermentative powers in the sugars ; both give rise under natural conditions 

 to acute or chronic disease in man and animals ; both are pathogenic to guinea- 

 pigs, setting up necrotic changes in the viscera ; both may give the Straus reaction 

 in male guinea-pigs ; and both are characterized by their extraordinary infectivity 

 for man in artificial cultures in the laboratory. There are, however, certain differ- 

 ences between them, the importance of which from the point of view of classification 

 it is difficult to assess. Thus Br. melitensis is a definite cocco-bacillus ; Pf. mallei, 

 though often occurring in very short forms, is generally described as a slender rod, 

 capable at times, especially in the animal body, of giving rise to long, and even 

 branching, thread-Uke forms (Mayer 1900, GalU-Valerio 1900). In culture, however, 

 it is not unusual for Pf. mallei to form short and almost ovoid bacilli, not unlike 

 Br. abortus. Antigenically, there is, in our experience, no apparent relationship 

 between Pf. mallei and organisms of the Brucella group (Wilson 1934). 



It may be pointed out that Pf. whitmori bears certain points of resemblance 

 to Friedlander's bacillus. Both these organisms are Gram-negative bacilli, and are 

 surrounded by a capsule or an interstitial substance, which is not infrequently 

 lost after artificial culture for some time. Both exhibit more or less similar 

 appearances in culture, and both give rise to an extremely viscous deposit in 

 broth. Both organisms give a cafe-au-lait growth on potato. Both are active 

 fermenters of sugars on first isolation, and both may tend to lose this property 

 after prolonged subculture in the laboratory. On the other hand, Pf. whitmori 

 difiers from Friedlander's bacillus in being motile, in liquefying gelatin, in failing 

 to produce gas from carbohydrates, and in its capability of giving rise to the 

 Straus reaction in the guinea-pig. 



Thompson (1933) draws attention to certain morphological and cultural similari- 

 ties between Pf. mallei and Pf. whitmori on the one hand and Actinohacillus lignieresi 

 on the other, and states that the organisms are antigenically related. His protocols, 

 however, furnish no evidence of specific cross-agglutination. The slight degree of 

 agglutination that was observed may quite well have been due to normal agglutinins. 

 Pf. mallei is frequently agglutinated by normal sera to a titre of 1/640 or over, 

 and the actinohacillus is often affected by normal sera, though usually to a lower 

 titre. Thompson's suggestion that all three organisms should be classified together 

 in the Mycobacterium group cannot be accepted until further evidence in support 

 of it is forthcoming. 



Some workers (Legroux and Djemil 1931, Legroux and Genevray 1933) regard 

 Pf whitmori as being more nearly related to Ps. pyocyanea than to Pf. 7nallei, but 

 the absence of pigment production by Pf. whitmori, and its demonstrated antigenic 

 affinity to Pf. mallei, render this doubtful. 



Pfeifierella mallei 



Isolation. — By Loeffler and Schiitz in 1882 (Loeffler 1886) from a horse dying of acute 

 glanders. 



Habitat. — Strict parasite ; found chiefly in equines and man. 



Morphology. — Slender rod-shaped organism, about l'5-3 fi X 0-3-0-6 /n broad. Straight 

 or shghtly curved, ends rounded, sides irregularly parallel or wavy ; arranged 

 singly, in pairs end-to-end, in parallel bundles, and in Chinese letter forms. In 



