Serological Identification of Dysentery Bacilli

Abstract

Antisera were prepd. by injecting rabbits with formalinized (0.3%) broth cultures at 5- to 7-day intervals in increasing doses until satisfactory agglutinin titers were reached (3-5 injns.). Shigella dysenteriae were washed before injn. When titers of 1:5, 120 or higher were reached or when no further increase occurred after additional injns., the animals were bled and the serum preserved with 0.5% phenol or by desiccation by the lyophile process. Antigens for the slide test were made by suspending the growth from 18- to 24-hr. agar slants in formalinized saline (0.3%) and adjusting the density approx. to Gates 1. The slide tests were performed on 5- to 7-in. glass slides divided by paraffin markings into sections approx. 1 X 2.5 cm. 72 tests could be made on one slide. 17 strains of S. dysenteriae have been identified by the slide test although none were isolated in Connecticut. 5 cultures of S. ambigua were typed including one from a Connecticut case. The majority of strains were in the Flexner group, distributed among the I, IIa, IIb, III, IV, V, and VI vars. The incidence of S. sonnei types is high and 264 strains were identified of which about 90% were isolated within the state. The results show that satisfactory serological identification of the pathogenic Shigella organisms can be made by the slide test. Strain identification in the detail that has been carried out may seem unnecessary and impractical at first thought. The majority of public health laboratories go only so far as to classify into the Flexner group, primarily because typing sera are not available. However, strain typing is essential if satisfactory epidemiology is to be done and detailed serological study is the only reliable means of typing. Not infrequently, coli-form and paracolon cultures have shown antigens in common with members of the Shigella group. Usually the reactions were minor and occurred with unadsorbed sera. The authors have also obtained agglutination of many of the paradysentery strains with certain Salmonella sera. These reactions have not been thoroughly investigated but the reciprocal reactions of Salmonella cultures in Shigella paradysenteriae antisera have usually been negative, and they could not be attributed to the type of group components that have been identified in the paradysentery organisms. Antigens similar to the Salmonella VI and XIII components have already been noted. A similar overlapping of physiol. characteristics has been pointed out between the various groups of the enteric organisms. The fact that organisms of the Enterobacteriaceae appear to be a continuous series of types, without sharp demarcation either as to physiol. or antigenic properties between the various sections, constitutes a problem to the "practical diagnostic bacteriologist." At present his best approach seems to be to use all available criteria for differentiation. Typical forms should offer little difficulty.[long dash]Horace Goldie.