Atividade antagonista de Shigella: pesquisa, extração, purificação e caracterização de uma nova bacteriocina

Abstract

Shigella is a common agent of inflammatory diarrhea worldwide. Bacteriocin production by Shigella sonnei employing the organism, other diarrheagenic bactéria, and members of the intestinal microbiota as indicator strains was evaluated. Over half of the strains expressed isoantagonism and heteroantagonism against Shigella flexneri and diarrheagenic Escherichia coli, indicating that bacteriocinogeny may represent a virulence factor for the bacterium. The intracellular fraction precipitated at 75% ammonium sulphate kept active following exposure to extreme pH values and maintenance at -80ºC for two years and was inactivated by high temperatures and proteases. After sequential steps of chromatography the molecular mass of the bacteriocin was estimated by mass spectrometry as 18,56 kDa. The N-terminal sequence of the bacteriocin did not match any other antibacterial protein described. The bacteriocin may represent a newly described protein or na already described protein with a newly detected function. Considering that S. sonnei producer strain showed antagonistic activity against diarrheagenic bactéria a potencial clinical applicability for the bacteriocin either for preventing or controlling diarrheal disease may be previewed. We also addressed bacteriocinogeny in S. sonnei and S. flexneri strains against E. coli K12Row and E. coli transformant strains carrying different bacteriocin plasmids by employing phenotypic and genotypic methods. Almost 40% of bacterial isolates expressed antagonism. All Shigella isolates harbor at least one bacteriocin determinant especially ColE4 and ColE7 plasmids, and more than 90% showed multiple bacteriocin genes. Data generated by this investigation confirms that bacteriocinogeny is a widespread ability among S. sonnei and S. flexneri and argues in favor of a key role for the phenomenon in mediating bacterial dynamics.