CONICET | Buscador de Institutos y Recursos Humanos

Biological activity and presence of DNA sequences related to virulence genes was studied in 21 strains of the Bacillus cereus group. The activity of spent culture supernatants and the effect of infection by vegetative bacterial cells were assessed on cultured human enterocytes (Caco-2 cells). The effect of the concentration of extracellular factors on the detachment of human enterocytes was studied. In addition, the ability to produce necrosis of enterocytes and the haemolytic activity were also studied. Concerning virulence genes, presence of the DNA sequences corresponding to the genes entS, entFM, nhe (A, B and C), sph, hbl (A, B, C and D), piplC and bceT were assessed by PCR. Ribopatterns were determined by an automated riboprinting analysis after digestion of the DNA with EcoRI. Principal component analysis and biplots were used to address the relationship between variables. Results showed a wide range of biological activity and variability in the occurrence of the DNA sequences tested. Two main clusters of ribopatterns were found. One of these clusters, includes all the strains that were positive for all the DNA sequences tested. Positive and negative correlations between variables under study were evidenced. Interestingly, high detaching strains were positively correlated with the presence of the sequences entS, nheC and sph. Within gene complexes, high correlation was found between sequences of the hbl complex. In contrast, sequences of the nhe complex were not correlated. Some strains clustered together in the biplots. These strains were positive for all the DNA sequences tested and they were able to detach enterocytes upon infection. Our results highlight the multifactorial character of the virulence of the Bacillus cereus group and showed the correlation between ribopatterns, DNa sequences and biological activity of the strains under study.