239. Epidemiologic Analysis of a Worldwide Collection of Escherichia coli ST131 Using the 1928D Core Genome (cg) Multilocus Sequence Type (MLST) Reveals Country Specific and Globally Disseminated Clades

Abstract

BackgroundIncreasing antimicrobial resistance (R) among Escherichia coli (EC) isolates can be associated with the expansion of the pandemic sequence type (ST) 131 that harbors virulence factors and causes more severe infections when compared with other antimicrobial-R EC. We evaluated the core genome MLST (cgMLST) profiles and R genes using the bioinformatics tool 1928D to evaluate the epidemiology of a global ST131 EC collection and unrelated STs.MethodsA total of 259 EC clinical isolates belonging to ST131 (n = 206), ST131-single loci variant (SLV; n = 25), and 28 non-ST131 isolates collected from 27 countries during 2016–2018 were selected. Whole-genome sequencing FASTQ files were uploaded to the 1928D pipeline to generate MLST, cgMLST and R gene prediction. cgMLST assignment was based on comparing >2,500 genes.ResultsAmong 231 ST131 and SLV EC isolates, 7 clades were identified (3 major [178 isolates]; Table) applying cgMLST allele distance (ad) of ≤50 as a cutoff. A total of 21 isolates were not assigned to clades (>50 ad from ST131 and SLV). Based on >95% concordance, 11 alleles differentiated clades II and III from clade I, while 6 alleles separated clades I and III from clade II. Isolates in clades I to IV were ciprofloxacin R (MIC, ≥4 mg/L); clades I and III predominantly carried blaCTX-M-15 (39/43 and 61/66), blaOXA-1 (35/43 and 43/66), and aac(6’)-Ib-cr (39/43, 45/66) while clade II carried blaCTX-M-14-like and rarely aac(6’)Ib-cr (3/69). The most ad between the 7 ST131 clades was 216, while unrelated STs showed variable ad among isolates within that ST. Isolates bellowing to ST1193 were closely related genetically (ad of 30), but other STs had more variability among isolates (ST167, ad 552; ST38, ad 150; and ST69, ad 179).Conclusion1928D is a robust platform for epidemiological analysis of isolates, providing additional granularity when compared with MLST. Clades II and III were closely related, but carried different blaCTX-M genes, while clades I and III were not as closely related, but both carried blaCTX-M-15, blaOXA-1, and aac(6’)Ib-cr. These findings suggest that these clades might have acquired R genes at different points in their genetic evolution. A threshold of ≤50 (cgMLST distance) was useful for classifying isolates into clades. Disclosures All authors: No reported disclosures.