[Value of antibiotype and bacteriocinotype for differentiating Shigella strains isolated in Argentina]

The aim of the present work was to analyse the phenotypical characteristics of Shigella strains in order to evaluate their possible utilisation as epidemiological markers. For one year, we studied 95 strains of Shigella obtained from stool specimens of patients with dysentery. Bacteria came from various health care centres in the states of Chaco and Corrientes (Argentina). Bacteria were identified by using classical biochemical methods. All strains were serotyped and susceptibility patterns were determined using thirteen antibiotics. Bacteriocin typing was determined by the sensitivity to piocins of Pseudomonas aeruginosa and to marcescins of Serratia marcescens. Colicin production in S. sonnei was also studied. Among all the strains examined, the most prevalent was Shigella flexneri (82%) followed by Shigella sonnei (18%). The most frequent serotype among S. flexneri was 2 (93%), followed by serotypes 6 (4%), 1 (1.5%), and 3 (1.5%). S. sonnei strains were classified in 7 antibiotypes, 6 piocin types, 3 marcescin types, and 4 colicin types. Strains of S. flexneri type 2 were divided among 14 antibiotypes, 4 piocin types and 2 marcescin types. Simpson's index of diversity was applied to evaluate the discriminatory power of studied typing methods, both alone and combined. Our results indicate that when taken independently, none of the evaluated typing methods had discriminative power, but when taken together, they may be successfully used for the epidemiological typing of Shigella strains.