A New Biotyping Scheme for Salmonella Typhimurium and its Phylogenetic Significance

Abstract

THE epidemiological value of different methods of distinguishing types within a bacterial species depends on their discriminating ability, reliability and ease of performance. Discriminating ability depends primarily on the number of types distinguished, but is poor if a large proportion of strains falls into a single type. Reliability depends on the reproducibility of each isolate's results in repeated tests and on the stability of the typing characters among different isolates from the same epidemic episode.Probably the best single method for differentiating types in Salmonella typhimurium is the phage-typing system of Callow (1943, 1951) , 1972). This method is less discriminating and more laborious than phage-typing, but it distinguishes different biotypes within individual phage-types, so that its combination with phage-typing gives a finer discrimination than either method alone (Kallings and Laurell, 1957;Rische and Kretzschmar, 1962;Lewis and Stocker, 1971).In a combined phage-typing and biotyping study of S. typhimurium we found some serious defects in the Kristensen scheme.(1) The fermentation tests with d-, Z-and rn-tartaric acids and citric acid proved unreliable and often gave different results on different occasions of testing the same isolate. Improved, more reliable methods were developed for the tartaric acids by Alfredsson et al.(1972) and these methods are used in the new scheme described in the present paper.(2) In our series of strains, both the original and the modified tests identified several biotypes with patterns of reactions different from those of the twenty-one types already recognised, but the new types could not be accommodated in the Kristensen classification in such a way as to show their relations to the existing types. For example, a group of strains designated " type 19Xd " by Morgenroth and Duguid (1968) resembled biotype 6 except that it was rhamnose negative; if this new type had been added to the scheme as type 22, its close relation to typ6 6 would not have been apparent. (3) We found that discrimination in biotyping could be improved by the addition of tests for the fermentation of trehalose in peptone water, fermentation of rhamnose in Bitter's medium, fermentation of inositol at 25"C, gas production from glucose, growthfactor requirements and presence of flagella and fimbriae, but the results of these extra tests could not be shown in any convenient way within the Kristensen classification. Mutational fermentation. Alfredsson et al. (1972)found that a major cause of unreliability in tests with the tartaric acids was the power of many non-fermenting strains to produce ~ ~~

Comparison of four methods of differential typing of isolates ofShigella sonnei

“…Previous biotyping studies with Salmonella typhimurium (Duguid et al 1975) and Escherichia coli (Crichton & Old, 1979) have indicated the need to read results of each biotyping test at definitive times that allow the inclusion of all genotypically positive strains and the exclusion ofall genotypically negative strains, a requirement not always recognised, however, in biotyping studies. Thus, the only biotyping characters that afforded discrimination among this series of isolates were maltose and rhamnose fermentation.…”

TracingSalmonella typhimuriuminfections

“…For multiple typing of S. typhimurium another method based on 15 biochemical characters has been developed (Duguid et al 1975). In this two-tier scheme 32 1 HYG 96 potential primary biotypes were recognized by the possible combinations of positive and negative reactions in the five most discriminating tests using the substrates D-xylose, meso-inositol, L-rhamnose, dextro and meso-tartrates and subtypes within these primary types were defined by the reactions in ten additional biotyping tests.…”

“…This is true not only of strains without plasmids and those which are phage untypable, as suggested by Holmberg et al (1984), but also of strains belonging to recognized phage types. The D-xylose, inositol, rhamnose and mneso-tartrate characters in the primary scheme of Duguid et al (1975) and most of the secondary characters are known to be chromosomally determined (Sanderson & Roth, 1983) and have been found to be stable in stored cultures and during epidemic spread (Duguid et al 1975;Anderson et at. 1978;Barker & Old, 1979;Barker, Old & Sharp, 1980).…”

“…All strains are typable and can be assigned to one of the 32 primary biotypes. The tests are reproducible and easy to perform (Duguid et al 1975). For these reasons, biotyping should be considered as a second method ancillary to either phage typing or plasmid analysis to determine the relatedness or unrelatedness of isolates.…”

Phage type/biotype groups of Salmonella typhimurium in Scotland 1974–6: variation during spread of epidemic clones

“…

SUMMARYBiotyping by the scheme of Duguid et al (1975) of 2010 cultures of Salmonella typhimurium received by the Scottish Salmonella Reference Laboratory in 1974-6, the definitive phage types of which were known, revealed 137 different phage type/biotype groups. Four major epidemic clones, comprising 52 % of the cultures, were recognized: 1/2a, 49/26a, 56/17g and 141/9f.

…”