Background. Escherichia coli is a highly clonal pathogen. Extraintestinal isolates belong to a limited number of genetically related groups, which often exhibit characteristic antimicrobial resistance profiles. Methods. We developed a rapid clonotyping method for extraintestinal E coli based on detection of the presence or absence of 7 single nucleotide polymorphisms (SNPs) within 2 genes (fumC and fimH). A reference set of 2559 E coli isolates, primarily of urinary origin, was used to predict the resolving power of the 7-SNP-based typing method, and 582 representative strains from this set were used to evaluate test robustness. Results. Fifty-four unique SNP combinations ("septatypes") were identified in the reference strains. These septatypes yielded a clonal group resolution power on par with that of traditional multilocus sequence typing. In 72% of isolates, septatype identity predicted sequence type identity with at least 90% (mean, 97%) accuracy. Most septatypes exhibited highly distinctive antimicrobial susceptibility profiles. The 7-SNP-based test could be performed with high specificity and sensitivity using single or multiplex conventional polymerase chain reaction (PCR) and quantitative PCR. In the latter format, E coli presence and septatype identity were determined directly in urine specimens within 45 minutes with bacterial loads as low as 102 colony-forming units/mL and, at clinically significant bacterial loads, with 100% sensitivity and specificity. Conclusion. 7-SNP-based typing of E coli can be used for both epidemiological studies and clinical diagnostics, which could greatly improve the empirical selection of antimicrobial therapy.
Bibliographical noteFunding Information:
Financial support. This material was supported by the National Institutes of Health (grant nos. R01AI106007 [to E. V. S.] and R41AI116114 [to ID Genomics, Inc]) and the Office of Research and Development, Medical Research Service, Department of Veterans Affairs (grant no. 1 I01 CX000192 01; to J. R. J.).
© The Author 2016. Published by Oxford University Press on behalf of the Infectious Diseases Society of America.
- Antibiotic resistance
- Clonal typing
- Escherichia coli
- Personal therapy
- Point-of-care testing