Virulence genes and subclone status as markers of experimental virulence in a murine sepsis model among Escherichia coli sequence type 131 clinical isolates from Spain.

Irene Merino,Patricia Ruiz-Garbajosa,Rafael Cantón,Stephen B Porter,Brian D Johnston,James R Johnson,Juan Pablo Horcajada,Evelyn Shaw,Connie Clabots,Concepción Gonzalez-Bello

doi:10.1371/journal.pone.0188838

Abstract

ObjectiveTo assess experimental virulence among sequence type 131 (ST131) Escherichia coli bloodstream isolates in relation to virulence genotype and subclone.MethodsWe analysed 48 Spanish ST131 bloodstream isolates (2010) by PCR for ST131 subclone status (H30Rx, H30 non-Rx, or non-H30), virulence genes (VGs), and O-type. Then we compared these traits with virulence in a murine sepsis model, as measured by illness severity score (ISS) and rapid lethality (mean ISS ≥ 4).ResultsOf the 48 study isolates, 65% were H30Rx, 21% H30 non-Rx, and 15% non-H30; 44% produced ESBLs, 98% were O25b, and 83% qualified as extraintestinal pathogenic E. coli (ExPEC). Of 49 VGs, ibeA and iss were associated significantly with non-H30 isolates, and sat, iha and malX with H30 isolates. Median VG scores differed by subclone, i.e., 12 (H30Rx), 10 (H30 non-Rx), and 11 (non-H30) (p < 0.01). Nearly 80% of isolates represented a described virotype. In mice, H30Rx and non-H30 isolates were more virulent than H30 non-Rx isolates (according to ISS [p = 0.03] and rapid lethality [p = 0.03]), as were ExPEC isolates compared with non-ExPEC isolates (median ISS, 4.3 vs. 2.7: p = 0.03). In contrast, most individual VGs, VG scores, VG profiles, and virotypes were not associated with mouse virulence.ConclusionsST131 subclone and ExPEC status, but not individual VGs, VG scores or profiles, or virotypes, predicted mouse virulence. Given the lower virulence of non-Rx H30 isolates, hypervirulence probably cannot explain the ST131-H30 clade's epidemic emergence.

Highlights

The spread of a specific Escherichia coli clone called sequence type 131 (ST131) is one of the key drivers of the rising prevalence of resistance to quinolones and cephalosporins among E. coli that cause urinary tract infections, with cephalosporin resistance being mainly due to expression of extended-spectrum beta-lactamases (ESBLs), CTX-M-15 [1,2,3]
Median virulence genes (VGs) scores differed by subclone, i.e., 12 (H30Rx), (H30 non-Rx), and (p < 0.01)
Of the 49 VGs tested, 32 (65%) were detected in at least 1 isolate, at frequencies ranging from 2% to 100% (Table 1) and all isolates encoded at least 8 VGs

Summary

Introduction

The spread of a specific Escherichia coli clone called sequence type 131 (ST131) is one of the key drivers of the rising prevalence of resistance to quinolones and cephalosporins among E. coli that cause urinary tract infections, with cephalosporin resistance being mainly due to expression of extended-spectrum beta-lactamases (ESBLs), CTX-M-15 [1,2,3]. The ST131 pandemic is driven mainly by two nested subclones within ST131, i.e., H30 (or clade C), which contains allele 30 of fimH (type 1 fimbriae), and H30Rx (or clade C2), a sublineage within H30 that often expresses CTX-M-15 [4]. Several studies have suggested that, apart from being extensively resistant, ST131 is highly virulent, with a higher capability of causing infection than other strains [5,6]. ST131 virulence has been assessed in different animal models [7,8,9] with different conclusions. These studies have not addressed ST131 subclone status

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Conclusion