A STUDY OF VARIATION OF SALMONELLA PULLORUM 1 



By H. Van Roekel, Chief of Laboratory 

 Poultry Disease Control 



INTRODUCTION 



Bacterial variation has been observed in numerous species of microorganisms, 

 according to Hadley, Lohnis and others. It is of interest to note that this phe- 

 nomenon or group of phenomena was recognized by some of the early investigators 

 in bacteriology, contrary to the generally accepted view that individual species 

 maintain their morphological and other characteristics with great constancy. 



Bacterial variation has received little attention in the study of pullorum 

 disease. From the many reports that have been published since the isolation of 

 the etiological agent by Rettger in 1899, we were until quite recently led to believe 

 that the organism is very stable in its morphological, cultural, pathogenic, and 

 serological properties. Variations in carbohydrate fermentations have been 

 reported, but the differences have been attributable in most instances to such 

 factors as culture media, incubation temperature, observation time, etc. 



Epornitics due to 5. pullorum have been found to occur in varying degrees of 

 intensity, showing that the organism may fluctuate widely in pathogenicity. A 

 most striking case may be cited in the fatal outbreak observed by Plastridge and 

 Rettger (1930) among young and adult domestic fowl. In this instance the adult 

 stock suffered rather heavy losses, which is. indeed, very uncommon in natural 

 outbreaks. Further details of this outbreak will be discussed later. 



Dearstyne, Kaupp, and Wilfong (1929) detected intermittent and low titre 

 reacting birds, but the relation of such reactions to the infecting organism was 

 not investigated. 



The employment of the macroscopic agglutination test as a diagnostic means 

 of detecting "carriers" of the causative organism has been and is recognized as 

 a progressive step in the control and eradication of the disease. While the testing 

 method has been improved and standardized to a high degree of efficiency, yet 

 certain important and perplexing problems still remain to be solved. In the routine 

 testing of flocks, doubtful or non-specific reacting birds may be encountered in 

 small numbers in most flocks and in large numbers in occasional flocks. Whether 

 cr not this problem will prove to be an everpresent one appears dependent upon 

 the insight that may be gained concerning the reagents and the factors involved 

 in antibody production and the agglutination phenomenon. To what extent 

 bacterial variation enters into this problem in nature is a question. 



It has been recognized for several decades that suitable strains are necessary 

 to produce a satisfactory antigen for the agglutination test. While attempts have 

 been made to designate certain strains and methods as standard in order to over- 

 come serological discrepancies and difficulties, certain problems still remain. 

 This fact has been observed in the eradication of pullorum disease where the 

 macroscopic agglutination test was employed. Further knowledge concerning 

 bacterial variation of 5. pullorum which will, in a measure at least, solve our 

 present problems may be anticipated. 



This investigation was stimulated by the fact that our present understanding 



'This bulletin covers in part the work submitted to the Graduate School of Yale University as 

 part requirement for the degree of Doctor of Philosophy. The writer desires to express his sincere 

 thanKs and appreciation to Professor Leo F. Rettger, Yale University, for his stimulating interest 

 and constructive criticism during this investigation: to Mr. 0. S. Flint for assisting in the photo- 

 graphic work; and to Doctor D. M. Yegian for technical assistance. 



