BacteriologyComparative study of Escherichia coli virulence determinants in strains causing urinary tract bacteremia versus strains causing pyelonephritis and other sources of bacteremia
Introduction
The virulence determinants and phylogenetic background of Escherichia coli strains that cause extraintestinal infections, such as several types of urinary tract infections (UTIs), cholangitis, meningitis, and bacteremia, have been under study for several years (Andreu et al., 1997, Cook et al., 2001, Johnson and Stell, 2000, Johnson et al., 2002, Maslow et al., 1995, Otto et al., 2001, Ruiz et al., 2002, Wang et al., 2002). The majority of strains producing these infections in noncompromised hosts belong to ECOR phylogenetic group B2, as defined by multilocus enzyme electrophoresis (Picard et al., 1999), and harbor genes encoding specialized virulence traits (Johnson et al., 1994, Johnson and Stell, 2000, Johnson et al., 2002, Johnson, 2003, Maslow et al., 1995). Thus, these strains have a highly virulent profile (Picard et al., 1999) and have been named extraintestinal pathogenic E. coli (ExPEC) (Johnson et al., 2002, Johnson, 2003). However, some questions remain open, such as the role played by particular virulence factors (VFs) in specific clinical syndromes or the pathogenic capability in a particular clinical context displayed by strains belonging to non-B2 groups.
To gain insight into the role of E. coli virulence determinants in the pathogenesis of bacteremia from a urinary tract origin, we collected strains isolated from patients with this condition and compared their virulence properties and phylogenetic background with those of E. coli strains from patients with pyelonephritis and negative blood cultures, and strains from patients with other sources of bacteremia.
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Strains and patients
A total of 150 E. coli strains isolated at the Microbiology Department were selected from patients seen at Hospital Vall d'Hebron (Barcelona, Spain) between 1996 and 2003. Of the 150 patients, 50 (17 males and 33 females with a mean age of 65 years) presented bacteremia originating in the urinary tract. Of these patients, 26 (52%) exhibited local predisposing factors for UTI and 13 (26%) were immunocompromised. Another 50 patients presented acute pyelonephritis with negative blood culture. This
Prevalence of ECOR phylogenetic groups, virulence genes, and O antigens
ECOR phylogenetic group B2 was the most frequent (Table 2), accounting for 95 of the 150 E. coli isolates (63%), followed by group D with 29 isolates (19%). Distribution of the phylogenetic groups among the 3 clinical syndromes was quite similar; however, E. coli strains producing non–urinary-source bacteremia were less represented by group B2 and more by group D. The most prevalent VF determinant, among the 150 isolates, was fimH, present in 97% of E. coli. The only 4 isolates without fimH had
Discussion
In the present study, we assessed the virulence characteristics of a new collection of E. coli strains causing urinary and non-urinary bacteremia and nonbacteremic pyelonephritis. To our knowledge, very few collections of bacteremia-causing E. coli strains have been characterized (Hilali et al., 2000, Johnson and Stell, 2000, Johnson et al., 2002, Olesen et al., 1998, Otto et al., 1993, Wang et al., 2002), although 2 of them (Johnson and Stell, 2000, Johnson et al., 2002) have been repeatedly
Acknowledgments
This work was supported by Fondo de Investigación Sanitaria (FIS 01/1353) and Fondo de Investigación Sanitaria (FIS 02/1887), Spain. We are grateful to Dr. M. Teresa Tórtola Fernández (Microbiology Department, Hospital Vall d'Hebron, Barcelona, Spain) for scientific assistance. We thank Mercè Villa (Microbiology Department, Hospital Vall d'Hebron, Barcelona, Spain) for assistance with statistical determinations and Dr. Mercedes Perez Melgosa (CTBT, Hospital Vall d'Hebron, Barcelona, Spain) for
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