The large-sized plasmids of enterohemorrhagic Escherichia coli O157 strains encode hemolysins which are presumably members of the E. coli α-hemolysin family

Abstract

Most enterohemorrhagic Escherichia coli O157:H7 strains harbor a large-sized (90 kb) plasmid designated pO157 and show an enterohemolytic phenotype. In this study the hemolytic activity of E. coli O157:H7 strain EDL933 was investigated. Curing of strain EDL933 from pO157 resulted in loss of its hemolytic activity. By transformation with Tn801-tagged pO157 (pSK3), the hemolysin-negative E. coli K-12 strains C600 and DH5 alpha became positive for hemolysin production. By transformation of recombinant plasmids carrying a 11.9 kb BamHI fragment and a 5.3 kb SalI fragment of pSK3 hemolytic activity is revealed when transformed in E. coli C600 or DH5 alpha DNA-hybridization of pO157 and subclones with the alpha-hemolysin specific DNA probe was only found under conditions of low stringency. No hybridization was found with enterohemolysin I (EHly1) and enterohemolysin II (EHly2) probes. Our results indicate that a hitherto not described hemolysin belonging to the alpha-hemolysin family is encoded by the 90 kb plasmid of E. coli O157 strains.

Escherichia coli produtora de toxina shiga (STEC): principais fatores de virulência e dados epidemiológicos

“…As cepas foram denominadas enterohemolíticas e não produziam alfa-hemólise em ágar sangue de carneiro convencional, mas pequenas e turvas zonas hemolíticas, após a incubação por 18 a 24 horas em ágar sangue com hemácias de carneiro lavadas, suplementado com cloreto de cálcio. Enquanto a alfa-hemolisina é codificada por genes cromossomais, os genes que codificam a enterohemolisina foram descritos em um plasmídio de 60 MDa, pO157, na cepa EDL 933 (SCHMIDT; KARCH; BEUTIN, 1994). Embora a enterohemolisina esteja presente na maioria dos isolados de EHEC/STEC e a enterohemólise sugerida como um marcador para detecção de EHEC (BEUTIN et al, 1996), sua contribuição na patogenicidade de EHEC/STEC ainda não foi esclarecida.…”

“…Sugeriu-se que a lise de eritrócitos pode fornecer ferro e estimular o crescimento de STEC (LAW; KELLY, 1995). O plasmídio pO157 está presente também em cepas do sorotipo O26:H11 e na maioria de STEC isoladas de humanos (BEUTIN et al, 1994;LEVINE et al, 1987), seus genes codificam outros possíveis marcadores de virulência adicionais: uma catalase-peroxidase (KatP) (BRUNDER et al, 1996) e uma serina protease (EspP), capaz de clivar o fator V de coagulação humano e de exacerbar a doença hemorrágica (BRUNDER et al, 1997).…”

VTEC enteropathogenicity

“…Enterohaemolysin is genetically related to E. coli oc-haemolysin (Schmidt et al 1995) and has a similar molecular ENTEROPATHOGENIC VTEC 175 mass of approximately 110kDa and a requirement for calcium ions for haemolytic activity (Beutin et al 1989). The role of enterohaemolysin in the pathogenesis of VTEC infections is unknown, but a very small number of patients with haemolytic uraemic syndrome, due to E. coli 0157, produce serum antibodies to enterohaemolysin (Schmidt et al 1994;Jenkins and Chart 1999), which suggests that enterohaemolysin is expressed during pathogenesis.…”

Colonization factors of Escherichia coli O157:H7 in pigs

“…When the plasmid is lost, experimentally or naturally, the hemolytic phenotype is lost (188, 231). Furthermore, when E. #6 DH5 alpha strains are transformed with the plasmid, they can convey hemolytic activity (188).The genes for the hemolysin have been mapped to the 0157 plasmid and are arranged in an operon fashion (189). The hemolysin has been characterized to be in the family of the alpha-like pore-forming RTX enterohemolysms (188,185,189).…”

“…Furthermore, when E. #6 DH5 alpha strains are transformed with the plasmid, they can convey hemolytic activity (188).The genes for the hemolysin have been mapped to the 0157 plasmid and are arranged in an operon fashion (189). The hemolysin has been characterized to be in the family of the alpha-like pore-forming RTX enterohemolysms (188,185,189). The EHEC-hly genes are highly conserved in the pO!57 plasmid, where as in non-0157 EHEC strains, the existence of this and other genes is much more sporadic (24,187).…”