Comparative study of pathogenicity tests for Shigella spp. and enteroinvasive Escherichia coli strains.

The purpose of this study was to optimize an in vitro pathogenicity model, as an alternative to Sereny test (on Guinea pigs). The study was performed on 13 Shigella spp. and 3 enteroinvasive Escherichia coli (EIEC) strains isolated in Romania between 2005 and 2007. The investigation implied the comparative evaluation between the Sereny test and Cravioto's adapted method for the assessment of the adherence and invasion capacity of the studied bacterial strains on HeLa cells, as well as the PCR detection of ipaH gene presence. The Sereny test was positive for all the strains tested. All strains adhered to the cellular layer, with a prevalent diffuse pattern for EIEC and an aggregative diffuse one for Shigella strains. The quantitative assessment of the invasion potential proved a high intracellular multiplication rate in 100% of the tested strains, with a progressive increase correlated with the incubation time. The present study has proven the existence of a good correlation between in vivo Sereny test and in vitro determination of the invasive capacity on eukaryotic HeLa cells, pleading for the utility of this test in identifying the invasive strains, taking into consideration the rigid regulations concerning the use of laboratory animals.