Ferric Dicitrate Transport System (Fec) of Shigella flexneri 2a YSH6000 Is Encoded on a Novel Pathogenicity Island Carrying Multiple Antibiotic Resistance Genes

Abstract

Iron uptake systems which are critical for bacterial survival and which may play important roles in bacterial virulence are often carried on mobile elements, such as plasmids and pathogenicity islands (PAIs). In the present study, we identified and characterized a ferric dicitrate uptake system (Fec) in Shigella flexneri serotype 2a that is encoded by a novel PAI termed the Shigella resistance locus (SRL) PAI. The fec genes are transcribed in S. flexneri, and complementation of a fec deletion in Escherichia coli demonstrated that they are functional. However, insertional inactivation of fecI, leading to a loss in fec gene expression, did not impair the growth of the parent strain of S. flexneri in iron-limited culture media, suggesting that S. flexneri carries additional iron uptake systems capable of compensating for the loss of Fec-mediated iron uptake. DNA sequence analysis showed that the fec genes are linked to a cluster of multiple antibiotic resistance determinants, designated the SRL, on the chromosome of S. flexneri 2a. Both the SRL and fec loci are carried on the 66,257-bp SRL PAI, which has integrated into the serX tRNA gene and which carries at least 22 prophage-related open reading frames, including one for a P4-like integrase. This is the first example of a PAI that carries genes encoding antibiotic resistance and the first report of a ferric dicitrate uptake system in Shigella.Pathogenicity islands (PAIs) are increasingly recognized as playing a vital role in bacterial virulence. PAIs are distinct virulence cassettes that often integrate into tRNA genes and encode bacteriophage-like integrases. Such islands may occupy large regions of the chromosome and often carry mobile elements, such as insertion sequences and transposons (25). PAIs have been found in many bacterial species, including Yersinia spp. (9, 13), enteropathogenic, enterohemorrhagic, and uropathogenic Escherichia coli (24,38,51), Salmonella enterica serovar Typhimurium (61), Vibrio cholerae (32), Helicobacter pylori (14), and Shigella flexneri (2,42,57,71). Some strains of uropathogenic E. coli and S. enterica serovar Typhimurium may harbor at least five PAIs (19,74). A variety of virulence determinants may be carried on PAIs, including genes encoding fimbriae, hemolysins (31, 64), type III secretion systems (15, 27), and iron uptake systems (13,42,71,75). Various Shigella spp. produce the siderophores enterobactin and/or aerobactin, which are involved in iron uptake (34, 50). The aerobactin locus in S. flexneri was recently shown to be carried on the SHI-2 PAI (42, 71). This was the first report of an iron transport system being carried on a PAI in Shigella.A number of PAI-like elements in Shigella spp. have been described. These include the SHI-2 PAI and a family of structurally related elements (42, 71) and the she PAI, which also belongs to a larger family of structurally related elements (2, 57). One of the characteristics of PAIs is their tendency to excise spontaneously from their sites of integration in the chromosome (26). In...

Prevalence of Pathogenicity Island II CFT073 Genes among Extraintestinal Clinical Isolates of Escherichia coli

“…Previous investigations by many different groups working with many different pathogens have demonstrated that the acquisition of iron is often essential for full virulence (8,16,44). In addition, many PAIs possess iron acquisition mechanisms (4,5,31). The locus encoding the FbpA-D iron siderophore system was previously shown to be associated with UPEC and to be more represented in these pathogens than in intestinal isolates of E. coli (43).…”

The Pathogenicity Island-Associated K15 Capsule Determinant Exhibits a Novel Genetic Structure and Correlates with Virulence in Uropathogenic Escherichia coli Strain 536

“…Several virulence-associated factors are encoded on this PAI, including the K15 capsule (ORF60 to 74), the recently described Pix fimbria-encoding gene cluster (ORF6 to 13) which belongs to the P adhesin family (33), and an autotransporter protein (ORF48) with the highest similarity to Sap, a putative autotransporter adhesin encoded on the she PAI of S. flexneri (GenBank accession no. AF326777 and AAL08472) (32). In addition to the corresponding virulence-associated determinants, a gene cluster (ORF16 to 19) is located on PAI V 536 that codes for a putative phosphoglycerate transport system (pgt) also present in S. enterica serovar Typhimurium LT2 and other UPEC strains (19,56).…”

Excision of the Shigella Resistance Locus Pathogenicity Island in Shigella flexneri Is Stimulated by a Member of a New Subgroup of Recombination Directionality Factors

“…and Vibrio cholerae, and in a variety of other pathogens, e.g., Escherichia coli, Helicobacter pylori, Yersinia enterocolitica, and Shigella flexneri (9). S. flexneri carries five distinct PAIs: Shigella island 2 (SHI-2), SHI-3, the she PAI, the Shigella resistance locus (SRL) PAI, and the mxi-spa gene cluster on the large virulence plasmid (1,13,15,17,28,29).…”