Comparison of four methods of differential typing of isolates ofShigella sonnei

Abstract

SUMMARYAn epidemiological study of Sonne dysentery in Dundee during the years 1971-6 was made by examining, in respect of 1420 isolates of Shigella sonnei, the discriminating power of colicine typing, antibiogram testing, biotyping and resistotyping and the stability of the markers they provided.Colicine typing identified nine colicine types, including four not previously described. However, because types 4 and 4 var., determined by col Ib, and type U, producing no colicines, accounted for 960 of the isolates, discrimination with colicine typing was poor. In antibiotic sensitivity tests, 13 different antibiogram patterns were noted. Less than 1 % of the isolates were sensitive to all of the eight antibiotics tested; most were multiply drug-resistant. Resistance to kanamycin, neomycin and paromomycin (KNP) was apparently due to a single resistance determinant, widely distributed in a majority (5300) of the isolates. When definitive times were chosen for reading each biotyping test, only maltose and rhamnose of the 13 'sugars' tested differentiated isolates into prompt-and late-fermenting types. Though the ability to ferment rhamnose was a stable property, it discriminated only 1X50% of the minority, late-fermenting type.Resistotyping with six chemicals discriminated eight epidemiologically valid resistotypes, including three new types. However, 93 % of the isolates belonged to only three resistotypes.Analysis of the data for isolates from 286 epidemiologically distinct episodes showed that the variability of colicine and antibiogram characters, found among isolates within, respectively, 40 and 280 of the episodes, was generally associated with loss or gain of a plasmid ('col I b-KNP') which determined production of colicine I b and KNP resistance. These characters varied both in vivo and in vitro. Variability of resistotype characters, on the other hand, was observed in only 28 (9 %) episodes, 14 of which possibly represented examples of mixed or sequential infections.For accurate epidemiological tracing of strains of Sh. sonnei in a community, resistotyping, the technique showing the greatest discrimination and least variability of the four tested, should be included as the principal typing method.HYo 87 12

Colicine production as an epidemiological marker for Shigella sonnei

“…Abbott and Graham (1961) pointed out the importance of having a standard medium as 'the activity of certain colicines such as those produced by type 6 and 7, is affected by small changes in the composition of the medium'. Helgason & Old (1981) showed that changes in the time of incubation of typing strains has a similar effect.…”

“…In contrast it had been reported by Fredericq (1948), that colicinogenic strains may lose the ability to produce colicines after prolonged storage. Recently, Helgason & Old (1981), reported, as very frequent, qualitative differences in observed colicine types among duplicate subcultures of the same isolates after storage and among different isolates of the same strain from episodes involving individual persons or members of the same family. As a result they concluded that the colicine typing method was highly unreliable for epidemiological studies.…”

Characterization of <i>Shigella sonne</i><i>i</i> Strains from Three Different Geographical Locations

“…Earlier studies have shown that colicin typ ing is not a reliable epidemiological marker because both quantitative and qualitative dif 48 Dhar/Ghafoor/Huq/Chugh S. sonnei from Three Geographical Locations ferences in colicin production by S. sonnei isolates have been noticed [7,10]. In contrast, other workers did not observe such differ ences [6,12].…”

“…Bacterial dysentery due to S' , sonnei con tinues to pose a serious health problem in developed countries as compared to other species of shigella which are more often iso lated from patients with dysentery in develop used only as a supplement to other markers because of the instability of certain colicinogenic strains [7][8][9][10]. Resistance to several an timicrobial agents has been demonstrated in shigella isolates from endemic areas.…”

“…Resistance to several an timicrobial agents has been demonstrated in shigella isolates from endemic areas. Drug resistance pattern, therefore, has also been used as an epidemiological marker as has been biotyping [1,[5][6][7]. The purpose of this study was to analyze the colicin type, biotype and the drug resis tance patterns of 5. sonnei isolated in Kuwait and to compare them with the strains ob tained from Saudi Arabia and Bangladesh.…”