Uropathogenic Escherichia coli 536 (06:K15:H31) carries two unstable DNA regions, which were shown to be responsible for virulence. These regions, on which the genes for hemolysin production (hly) and P-related fimbriae (prj) are located, are termed pathogenicity islands (PAI) I and II, and were mapped to positions 82 and 97, respectively, on the E. coli K-12 linkage map. Sequence analysis of the PAI region junction sites revealed sequences of the leuX and selC loci specific for leucine and selenocysteine tRNAs. The tRNA loci function as the targets for excision events. Northern (RNA) blot analysis revealed that the sites of excision are transcriptionally active in the wild-type strain and that no tRNA-specific transcripts were found in the deletion mutant. The analysis of deletion mutants revealed that the excision of these regions is specific and involves direct repeats of 16 and 18 nucleotides, respectively, on both sides of the deletions. By using DNA long-range mapping techniques, the size of PAI I, located at position 82, was calculated to be 70 kb, while PA II, mapped at position 97, comprises 190 kb. The excision events described here reflect the dynamics of the E. cohi chromosome.
The uropathogenic Escherichia coli strain 536 (O6:K15:H31) carries two unstable DNA regions on its chromosome which were termed pathogenicity islands (Pais). Both pathogenicity islands, Pai I and Pai II, are incorporated into tRNA specific loci: Pai I is located in the tRNA gene for selenocysteine (selC), and Pai II is integrated in the leucine-specific tRNA locus leuX. Mutant strain 536-21 has lost the two pathogenicity islands together with the intact tRNA genes. While 536 is a virulent strain, 536-21 has lost a number of properties, including in vivo virulence. In previous publications we reported that the genes coding for two haemolysins (hly I, hly II) and P-related fimbria (prf) are located on the Pais. In this paper, we demonstrate that the expression of other gene products influencing metabolic properties in addition to in vivo virulence are strongly dependent on the intact tRNA loci selC and leuX. In order to determine the influence of the two tRNAs on the expression of these properties, the genes selC and leuX were cloned from the genome of strain 536 and then introduced into the mutant 536-21. Our results clearly show that the seleno-cysteine-specific tRNA (tRNA(Sec)) directly influences the ability of the bacteria to grow under anaerobic conditions, because selenocysteine is part of the enzyme formate dehydrogenase (FDH) which is involved in mixed acid fermentation. The rare leucine-specific tRNA5(Leu), encoded by leuX, influences a number if properties including type 1 fimbria production, flagellation and motility, production of enterobactin and serum resistance, and is also necessary for full in vivo virulence. While the tRNA(Sec) is directly involved in the production of FDHs, the leuX specific tRNA5(Leu) appears to influence the expression of various factors through specific transcriptional or translational control mechanisms.
Escherichia coli isolates of serotype O6 show a broad spectrum of virulence: virulent strains often cause urinary tract infections; other strains are considered nonpathogenic. In order to analyze the properties of E. coli O6 strains, different phenotypic and genotypic test systems were used. Our data indicate that O6 strains represent a rather heterogenous group of bacteria, which differ in the genotypic presence as well as in the phenotypic expression of virulence factors. In contrast to the isolates 536 (O6:K15) and RZ 475 (O6:K5) the strain DSm 6601, belonging to serotype O6:K5:H1, produces neither toxins nor mannose-resistant hemagglutinating (MRHA) adhesins. However, the strain possesses chromosomally located gene clusters coding for F1C (foc) and type I fimbriae (fim). In addition, the strain secrets the iron-uptake substances aerobactin and enterobactin and produces at least one microcin. The strain is serum-sensitive and is less virulent in in vivo animal tests.
A total of 127 extraintestinal Escherichia coli strains of the capsule serotypes Kl, K5, and K100 from human and animal sources were analyzed for DNA sequences specific for the genes for various adhesins (P fimbriae [pap] and P-related sequences [prs], S fimbriae [sfa]IFIC fimbriae [foc], and type I fimbriae [fim]), aerobactin (aer), and hemolysin (hly). The expression of corresponding virulence factors was also tested. Twenty-four selected strains were analyzed by long-range DNA mapping to evaluate their genetic relationships. DNA sequences for the adhesins were often found in strains not expressing them, while strains with hemolysin and aerobactin genes usually did express them. Different isolates of the same serotype often expressed different virulence patterns. The use of virulence-associated gene probes for Southern hybridization with genomic DNA fragments separated by pulsed-field gel electrophoresis revealed that a highly heterogeneous restriction fragment length and hybridization pattern existed even within strains of the same serotype. Long-range DNA mapping is therefore useful for the evaluation of genetic relatedness among individual isolates and facilitates the performance of precise molecular epidemiology.Escherichia coli strains of the Ki capsular serotype represent 80% of all E. coli strains isolated from cases of newborn meningitis and sepsis in humans (24,57,63). Moreover, Kl strains and isolates of other serotypes, including 018:K5 and 075:K100, are able to cause urinary tract infection, and Kl E. coli isolates are also often found to be the causative agent of systemic infections in animals (3,48,64,70,71).It has been clear for several years that the capsular antigens, especially Kl and certain types of 0 antigen, are strongly associated with such extraintestinal infections (4, 33, 60, 61, 64), as are specific fimbrial adhesins (18,42,45,46), hemolysin (Hly) (20,22,23), and aerobactin (Aer) (11,28,37). Extraintestinal E. coli isolates may carry different types of fimbrial adhesins which can be distinguished serologically (47) and can show different binding properties. P fimbriae (also termed Pap pili [45]) are associated with pyelonephritis and recognize an Ot-D-galactosyl-(1-4)-p-galactose receptor (29, 66). P-related sequences (Prs) mediate binding to galactosyl-N-acetyl-(ox1-3)-galactosyl-N-acetyl residues (40). The S-fimbrial adhesin (Sfa) interacts with a-sialyl(2-3p)-D-galactose receptor molecules (32,54). Another adhesin, the type I fimbrial adhesin, is produced by pathogenic and nonpathogenic strains and is able to bind to a-D-mannose-containing receptors (47). Fimbriae of serotype FIC are unable to agglutinate erythrocytes but do seem to interact with cells of the human urinary tract (56,68,69).E. coli strains may be subdivided into clones by electrophoretic typing of alloenzymes (4) and by outer membrane protein (OMP) profiles (3). In some cases, the clones have a characteristic serotype based on the 0 lipopolysaccharide and K capsular antigens (4). Attempts have been made to * Corres...
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