Characterization of four Escherichia coli clonal groups

This thesis summarizes the history and current knowledge of virulence factors and antimicrobial resistance of four distinctive pathogenic Escherichia coli clonal groups, i.e., O15:K52:H1, O117:K1:H7, O78:H10, and ST131, based on a literature review and the results of seven studies by the author. Paper I describes an analysis of 100 archived international E. coli O15:K52:[H1] clinical isolates (1975 2006) for diverse phenotypic and molecular traits in relation to year. This analysis showed that over time the O15:K52:H1 clonal group has become increasingly resistant to antimicrobials while maintaining (or extending) its virulence gene repertoire, possibly contributing to its expansion. Paper II describes a novel Shigatoxin-producing E. coli (STEC) O117:K1:H7 clonal group, based on an analysis of stool isolates (1997 2002) from 20 Danish patients returning from Africa and Asia with chronic watery diarrhea. The isolates typically contained stx1. lacked stx2, eae, saa, and ehxA, were multidrugresistant (65%), and were clonally related by PFGE. These findings established O117:K1:H7 STEC as a potential cause of chronic watery diarrhea in returning international travelers. Paper III uniquely reports human disease involving E. coli O78:H10, based on an analysis of 19 isolates (1 fecal, 18 urine) from a urinary tract infection outbreak of undetermined source in Copenhagen (1991-1992) that involved an unusual multi-resistant E. coli O78:H10 strain. Surprisingly, the isolates qualified as enteroaggregative E. coli (EAEC), a diarrheagenic pathotype, making this the first reported involvement of EAEC in an extraintestinal disease outbreak. Paper IV reports an analysis of 51 archived E. coli O78:H10 isolates (1956 2000) that showed E. coli O78:H10 to be clonally heterogeneous, comprising one dominant clonal group (61% of isolates, including all 19 Copenhagen outbreak isolates) from ST10 (phylogenetic group A), plus several minor clonal groups (phylogenetic groups A and D). The outbreak clone exhibited both extraintestinal pathogenic E. coli (ExPEC) and EAEC characteristics. Paper V reports evidence that the outbreak strain adhered more extensively to human bladder epithelial cells than did prototype uropathogenic (ExPEC) strains thanks to its aggregative adherence fimbriae, the principal adhesins of EAEC, and was capable of extensive biofilm formation on urethral catheters. These findings suggest that certain EAEC-specific virulence factors increase uropathogenicity. Paper VI reports a search for ST131, a globally disseminated, recently emerged multiresistant ExPEC clonal group, among 115 extended-spectrum beta-lactamase (ESBL)-producing E. coli clinical isolates from Danish patients (2008 2009), to assess ST131's prevalence in Copenhagen among ESBL-producing isolates. ST131 was the most prevalent clonal group (38% of isolates) and compared with other ESBL isolates was more often community-associated and exhibited distinctive and extensive virulence profiles. Paper VII reports temporal trends in antimicrobial resistance and virulence genes among historical E. coli ST131 isolates (1968 2011). Antimicrobial resistance increased over time due to emergence of the (resistance-associated) H30 and H30-Rx ST131 subclones. Distinctive characteristics of the ST131 H30-Rx subclone including specific virulence factors (iutA, afa/dra, kpsM II), K100 capsule, multidrug resistance, and ESBL production possibly contributed to this lineage's epidemiologic success. These findings confirm that ST131 represents a group of distinctive subclones, not a unitary entity. In conclusion, all four clonal groups were multiresistant and demonstrated the potential to spread locally or globally. A combination of antimicrobial resistance and specific virulence genes likely contributed to their epidemiologic success. Future implementation of rapid methods to screen for such multiresistant high-risk clones and their cardinal virulence genes conceivably could assist in clinical management and prevention efforts.