Dominance of ST131Escherichia colicarryingblaCTX-Min patients with bloodstream infections caused by cephalosporin-resistant strains in Australia, New Zealand and Singapore: whole genome analysis of isolates from a randomised trial
Synopsis/AbstractObjectivesTo characterise multi-drug resistantEscherichia coliisolated from patients in Australia, New Zealand and Singapore with bloodstream infection (BSI).MethodsWe prospectively collected third-generation cephalosporin resistant (3GC-R)E. colifrom blood cultures obtained from patients enrolled in a randomised controlled trial. Whole genome sequencing was used to characterise antibiotic resistance genes, sequence types (STs), plasmids and phylogenetic relationships. Antibiotic susceptibility was determined using disk diffusion and Etest.ResultsA total of 70E. coliwere included, of which the majority were ST131 (61.4%). BSI was most frequently from a urinary source (69.6%), community-associated (62.9%) and in older patients (median age 71 years [IQR 64-81]). The median Pitt bacteraemia score at presentation was 1 (IQR 0-2, range 0-3) and ICU admission was infrequent (3.1%). ST131 possessed significantly more acquired resistance genes than non-ST131 (p=0.003). Clade C1/C2 ST131 predominated (30.2% and 53.5% of all ST131 respectively) and these were all resistant to ciprofloxacin. All clade A ST131 were community-associated. The predominant ESBL types wereblaCTX-M(78.6% of isolates) and were strongly associated with ST131, with the majorityblaCTX-M-15. Clade C1 was associated withblaCTX-M-14andblaCTX-M-27, whereasblaCTX-M-15predominated in clade C2. Plasmid-mediated AmpC (p-AmpC) genes (mainlyblaCMY-2) were also frequent (17.1%) but were more common with non-ST131 strains (p< 0.001). The majority of plasmid replicon types were IncF.ConclusionsIn a prospective collection of 3GC-RE. colicausing BSI in the Australasian region, community-associated Clade C1/C2 ST131 predominate in association withblaCTX-MESBLs, although a significant proportion of non-ST131 strains carriedblaCMY-2.