VARIATION OF SALMONELLA PULLORUM 21 



xl 



XI \ Isolated from a hen in 1933 



XIIJ 



XIII Isolated from a chick in 1933 



XIV Isolated from a young pullet in 1932 



XV Isolated from a chick in 1933 



All but two of the strains exhibited characteristics typical of S. pullorum. 

 Number VII was an old strain which had acquired the property of fermenting 

 maltose since it was first isolated. In other respects it appeared to be typical. 

 Strain XIV, which was isolated from a young pullet in 1932, revealed cultural 

 characteristics different from 5. pullorum in that it grew with difficulty in different 

 media, settled out in broth culture, and produced some atypical colonies and 

 cell forms. 



The growth appearance of the different strains in broth from day to day re- 

 sembled that of 5. pullorum, with the exception of Strain XIV, which settled out 

 in every instance. After the fifth transfer this strain was streaked on plain meat 

 extract agar; this yielded colonies which possessed the features of the "normal" 

 type. 



Meat extract agar plates were streaked from the last set of broth cultures of 

 the 14 inoculated sets. The character of the growth on the plates after an incuba- 

 tion period of 24 hours and longer at 37° C. was, in every instance, that of typical 

 strains. 



One month after the last set of broth tubes was inoculated all of the broth cul- 

 tures were streaked on agar plates. All strains exhibited some degree of colony 

 variation from the normal. However, some strains varied more than others. 

 This was also true of a single strain which was inoculated into different broth 

 tubes. In the majority of the broth tubes little or no variation was observed. 

 In those instances where colony variation was most evident agar plates were 

 again streaked. The results revealed no sign of colony variation in some of the 

 strains, while others produced colonies that in some instances were markedly 

 different from the typical. 



Through a process of further selection of the colonies that varied from the 

 normal, and by repeated transfer, three definite variants were obtained. Variants 

 VHI-a and IX-a were cultivated on meat extract agar and transferred at frequent 

 intervals, always selecting the roughest colony type. These two types appeared 

 to have undergone a profound change in their colonial morphology; they appeared 

 very stable. Variants Vl-a and IX-a were placed on liver infusion agar and 

 transferred at frequent intervals. Variant VI -a exhibited a colony type that was 

 not greatly different from the typical on this medium. The degree of colonial 

 roughness varied from time to time, but it never approached the marked roughness 

 of Strain IX-a. The properties of the three variants will be described later in this 

 section. The remaining strains, while they did exhibit slight variation in colony 

 morphology, reverted to the normal type after a few transfers on agar. 



Four sets of broth cultures were streaked on meat extract agar plates two and 

 one-half months after the last set of broth tubes was inoculated. Negative results 

 were obtained in attempts to isolate definite colony variants. 



At five and one-half months the same broth cultures were again streaked on 

 agar plates. Three variants were isolated from Strains I, II, and XV. The variant 

 from Strain XV gradually reverted to the parent type. The other two variants 

 (designated as I-a and Il-a) were maintained on liver infusion agar through 

 frequent transfer. 



