The Plasmid of Escherichia coli Strain S88 (O45:K1:H7) That Causes Neonatal Meningitis Is Closely Related to Avian Pathogenic E. coli Plasmids and Is Associated with High-Level Bacteremia in a Neonatal Rat Meningitis Model

Abstract

A new Escherichia coli virulent clonal group, O45:K1, belonging to the highly virulent subgroup B2 1 was recently identified in France, where it accounts for one-third of E. coli neonatal meningitis cases. Here we describe the sequence, epidemiology and function of the large plasmid harbored by strain S88, which is representative of the O45:K1 clonal group. Plasmid pS88 is 133,853 bp long and contains 144 protein-coding genes. It harbors three different iron uptake systems (aerobactin, salmochelin, and the sitABCD genes) and other putative virulence genes (iss, etsABC, ompT P , and hlyF). The pS88 sequence is composed of several gene blocks homologous to avian pathogenic E. coli plasmids pAPEC-O2-ColV and pAPEC-O1-ColBM. PCR amplification of 11 open reading frames scattered throughout the plasmid was used to investigate the distribution of pS88 and showed that a pS88-like plasmid is present in other meningitis clonal groups such as O18:K1, O1:K1, and O83:K1. A pS88-like plasmid was also found in avian pathogenic strains and human urosepsis strains belonging to subgroup B2 1 . A variant of S88 cured of its plasmid displayed a marked loss of virulence relative to the wild-type strain in a neonatal rat model, with bacteremia more than 2 log CFU/ml lower. The salmochelin siderophore, a known meningovirulence factor, could not alone explain the plasmid's contribution to virulence, as a salmochelin mutant displayed only a minor fall in bacteremia (0.9 log CFU/ml). Thus, pS88 is a major virulence determinant related to avian pathogenic plasmids that has spread not only through meningitis clonal groups but also human urosepsis and avian pathogenic strains.Escherichia coli is the second cause of neonatal bacterial meningitis in industrialized countries, after group B streptococci. Despite advances in neonatal care, E. coli neonatal meningitis (ECNM) remains a potentially devastating illness, with a mortality rate of 10 to 15% and neurological sequelae in 30 to 50% of cases (8,20,28,29,62). Like most extraintestinal pathogenic E. coli (ExPEC) strains, ECNM strains mainly belong to phylogenetic group B2 and compose a small number of

Plasmid-Encoded Iron Uptake Systems

“…Genes coding for aerobactin, salmochelin, and the Sit systems have been found on non-ColV plasmids of E. coli, Salmonella, and Klebsiella that are often associated with antibiotic resistance genes (38,51,62,75,102,151). Occurrence of resistance determinants on ColV plasmids from different bacterial hosts has also been reported (29,41,42).…”

“…Colicin V is often found in association with colicin Ia (50). Plasmid pS88 is an example of a plasmid harboring colicin V and colicin Ia operons (51). Colicin Ia has the same mode of action as colicin V, but while the production of colicin Ia is induced under stress conditions, the expression of colicin V is regulated by iron (49,52).…”

“…In extreme cases, plasmids can lack the entire variable region. There is also an example of a strain harboring the constant region on one plasmid and part of the variable region (the eit operon) on another (31,51,126).…”

“…In whole-plasmid transcriptional studies, an additional gene, shiF, was upregulated during growth in human serum and urine and in a neonatal rat sepsis model (93,94). The shiF gene has been found to be conserved upstream of the aerobactin cluster, in some cases in association with another gene, viuB (51,(64)(65)(66). Based on their homology, the products of these two genes have been proposed to be part of the aerobactin iron uptake system (64)(65)(66)93).…”

Unusual “Flesh-Eating” Strain ofEscherichia coli

“…The strain carried genes encoding adhesins (P fimbriae with adhesin PapGIII but not PapGII, Sfa/F1C fimbriae, and heat-resistant agglutinin [hra]), iron-acquisition systems (including yersiniabactin, salmochelin, and the Sit system but not aerobactin), and toxins (such as alpha-hemolysin [hly], cytotoxic necrotizing factor 1 [cnf1], vacuolating toxin, and colibactin but not the secreted autotransporter toxin nor the cytolethal distending toxin). Finally the strain had no other genetic determinants (colicin V, colicin Ia, iss, etsABC, OmpT, hlyF) that were specific to a large plasmid carried by the highly virulent E. coli strain S88 recently sequenced (13). Twenty well-characterized human genetic polymorphisms that have been associated with severe sepsis susceptibility or severity, multiple organ dysfunction syndrome, and coagulation disorders (7) were searched.…”