INVESTIGADORES
PEREZ Pablo Fernando
congresos y reuniones científicas
Título:
Virulence of Bacillus cereus: lessons from an invertebrate infection model
Autor/es:
MINNAARD, J.; BUISSON, C.; PÉREZ, P. F. AND NIELSEN-LEROUX, C
Reunión:
Congreso; XXIII Congreso Latinoamericano de Microbiología. XIV Congreso Argentino de Microbiología.; 2016
Resumen:
Bacillus cereus is a sporeforming microorganism closely related to the entomopathogen B. thuringiensis. It is involved in intestinal and non-intestinal pathologies in humans. The virulence of B. cereus is due to the production of several extracellular factors as well as the ability to adhere/invade eukaryotic cells. However, its mechanisms of pathogenesis are not fully understood. The present study aimed to gain insight on the pathogenesis of B. cereus by using larvae of the honeycomb, greater wax moth, Galleria mellonella (Gm) as the infection model. Strains B10502, T1, 2 and M2 of B. cereus were grown in LB broth to mid-log phase, harvested by centrifugation, suspended in NaCl 0.85 % (w/v) at different concentrations. Last instar Gm larvae were infected by oral or intra-haemocoele routes (20 larvae per condition). Infections by oral route were performed in the presence or not of Cry toxin from B. thuringiensis. This toxin leads to the degradation of the perithrophic matrix (PM), a mucus rich structure that separates lumen content from the intestinal epithelium, thus enhancing spreading of orally inoculated bacteria. At different time points, death ratios of larvae and melanization were evaluated. After dissection, the PM and intestine were analysed by microscopy and naked eye inspection.By oral route, the synergistic effect of the toxin Cry was strongest for strain B10502. Mortality ranged from 15 % to around 50 % without and with toxin Cry respectively with doses of 2 x 106 bacteria/larvae. Some dead larvae infected with strains 2 and M2 did not show any melanization. Even without Cry toxin, larvae infected with T1 strain revealed damage in PM but no effects were found in larvae infected with B10502 strain. Higher bacterial loads were found in the PM of T1-infected larvae as compared with those infected with B10502 strain. Intestines showed low bacterial loads for all strains under study. When bacteria were inoculated in the haemocoele, lower doses were required to kill the larvae. There were differences between the virulence of the different strains tested being the strain T1 the one with the strongest biological effects (20 % mortality with 30 bacteria inoculated per larva). At these doses, the less active strain B10502 showed no lethal effects. Higher doses (2.4 x 103 bacteria/larva) led to 60 % and 40 % mortality for strains T1 and B10502 respectively. Strains T1 and B10502, leading to opposite responses in the Gm model, have demonstrated different effect in in vitro tests. In addition, they have different genetic background related to virulence markers.The results of the present study, demonstrate the usefulness of the Gm model as an alternative system to gain insight on the virulence of B. cereus. Given that vertebrates and invertebrates share many common mechanisms of the innate immune response, this model could be appropriate to unravel the main steps of the immune defence against B. cereus.