Abstract
Most of the knowledge of the virulence determinants of extraintestinal pathogenic Escherichia coli (ExPEC) comes from studies with human strains causing urinary tract infections and neonatal meningitis and animal strains causing avian colibacillosis. In this research, we analyzed the phylogenetic background, the presence of 20 ExPEC virulence factors, and the intrinsic virulence potential of 74 E. coli strains isolated in São Paulo, Brazil, from 74 hospitalized patients (43 males and 31 females) with unknown-source bacteremia. Unlike other places in the world, the bacteremic strains originated equally from phylogroups B2 (35%) and D (30%). A great variability in the profiles of virulence factors was noted in this survey. Nevertheless, 61% of the strains were classified as ExPEC, meaning that they possessed intrinsic virulent potential. Accordingly, these strains presented high virulence factor scores (average of 8.7), and were positively associated with 12 of 17 virulence factors detected. On the contrary, the non-ExPEC strains, isolated from 39% of the patients, presented a generally low virulence capacity (medium virulence factor score of 3.1), and were positively associated with only the colicin cvaC gene. These results show the importance of discriminating E. coli isolates that possess characteristics of true pathogens from those that may be merely opportunistic in order to better understand the virulence mechanisms involved in extraintestinal E. coli infections. Such knowledge is essential for epidemiological purposes as well as for development of control measures aimed to minimize the incidence of these life-threatening and costly infections.
Highlights
Progress has undoubtedly been achieved in the last decade in the knowledge of bacterial pathogenesis mechanisms and the complex molecular events involved in host-pathogen interactions
Origin and growth conditions of the bacterial strains This study included 74 E. coli bacteremia isolates from 74 patients hospitalized in a tertiary level hospital located in Sao Paulo city, Brazil, which is a cosmopolitan area encompassing a population of about 11 million inhabitants
Data are reported as number with percent in parentheses. aThe genes clpG, ehxA and espP were not detected. bTotal number of strains in the group. * P,0.05, frequency of virulence factors in each phylogenetic group compared to the frequency in all others (Fisher exact test). +Negative association between the phylogroup and the virulence factor
Summary
Progress has undoubtedly been achieved in the last decade in the knowledge of bacterial pathogenesis mechanisms and the complex molecular events involved in host-pathogen interactions. Infectious diseases are still the cause of significant morbidity and mortality in both human beings and animals. As many as 90% of the E. coli strains are commensals inhabiting the intestinal tract of humans and warm-blooded animals, and rarely cause disease. Some strains are provided with a wide variety of virulence factors (VFs) that enable them to be the etiological agents of various intestinal or extraintestinal diseases [1]. Phylogenetic analysis has classified E. coli strains into four main phylogenetic groups (A, B1, B2, and D). Most of the virulent extraintestinal human strains belong to phylogroup B2, and to a lesser extent to group D [2], while many poultry pathogens belong to phylogroup A [3]. Intestinal pathogenic E. coli are predominantly B1 strains. Commensal E. coli, usually included in groups A and B1, may have originated from any of the phylogenetic groups, depending on the geographical region studied [4]
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