Predominance of the fimH30 Subclone Among Multidrug-Resistant Escherichia coli Strains Belonging to Sequence Type 131 in Italy

TO THE EDITOR—We read with interest the article by Johnson et al, which demonstrates that, in extraintestinal pathogenic Escherichia coli (ExPEC), fluoroquinolone (FQ) resistance is currently associated with the rapid expansion of a single dominant multidrug-resistant (MDR) strain that emerged within sequence type (ST) 131 [1]. Although the strong predominance of the ST131 clone has been well described in the literature since 2008 [2– 5], the peculiarity of Johnson et al’s study was to analyze historical and recent ST131 isolates at the sub-ST level, revealing that a specific fimH-based subclone (H30) is currently responsible for most FQ-resistant ExPEC infections, at least in the United States. This H30 subclone was demonstrated to possess a unique and conserved gyrA/parC allele combination conferring FQ resistance, and the authors rightly commented on these data in support of its strict clonality. We are particularly interested in this issue, since ST131 is also currently predominant among MDR ExPEC in Italy and because some ST131 strains we previously analyzed were found to carry the same pattern of gyrA/parC substitutions described by Johnson et al [1, 6]. No information is available on the fimH-based subclones circulating in European countries. In this study, 172 ExPEC strains isolated from cases of urinary tract infections and sepsis in Italy during April 2012– December 2012 were analyzed. Staff a the 3 enrolled hospitals were asked to collect all consecutive MDR E. coli strains and 1 ciprofloxacin-susceptible non-MDR E. coli strain for every 3 MDR strains collected. “MDR” was defined as resistance to at least 3 antimicrobial agents of different classes (ampicillin, third-generation cephalosporins, ciprofloxacin, gentamicin, and trimethoprim/sulfamethoxazole). Of 172 strains, 119 were MDR strains that were resistant to ciprofloxacin; 9 were MDR strains that were susceptible to ciprofloxacin; and 44 were non-MDR strains that were susceptible to ciprofloxacin. Antimicrobial susceptibility testing, phylogenetic typing, polymerase chain reaction screening for ST131 followed by confirmation (by mdh and gyrB gene sequencing), characterization of the extended-spectrum β-lactamase (ESBL) and/or AmpC genes, and fimH-based subtyping of the ST131 strains were performed as previously described [1, 7–9]. To investigate which fimH allele circulated in Italy before 2012, an additional 91 E. coli ST131 strains previously identified were also subtyped [7, 10]. Of these 91 strains, 28 (24 ciprofloxacinresistant strains and 4 ciprofloxacinsusceptible strains) were isolated in 2006, and 63 (58 ciprofloxacin-resistant strains and 4 ciprofloxacin-susceptible strains) were isolated in 2009. By phylogenetic typing, overall, the majority of strains isolated in 2012 (110/ 172 [64%]) fell into phylogenetic group B2, followed by groups D (30/172 [17.4%]),