Implications of stx loss for clinical diagnostics of Shiga toxin-producing Escherichia coli
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The dynamics related to the loss of stx genes from Shiga toxin-producing Escherichia coli remain unclear. Current diagnostic procedures have shortcomings in the detection and identification of STEC. This is partly owing to the fact that stx genes may be lost during an infection or in the laboratory. The aim of the present study was to provide new insight into in vivo and in vitro stx loss in order to improve diagnostic procedures. Results from the study support the theory that loss of stx is a strain-related phenomenon and not induced by patient factors. It was observed that one strain could lose stx both in vivo and in vitro. Whole genome comparison of stx-positive and stx-negative isolates from the same patient revealed that different genomic rearrangements, such as complete or partial loss of the parent prophage, may be factors in the loss of stx. Of diagnostic interest, it was shown that patients can be co-infected with different E. coli pathotypes. Therefore, identification of eae-positive, but stx-negative isolates should not be interpreted as “Shiga toxin-lost” E. coli without further testing. Growth and recovery of STEC were supported by different selective agar media for different strains, arguing for inclusion of several media in STEC diagnostics.
KeywordsSTEC diagnostics stx-loss EHEC diagnostics Phage excision Selective culture media
We thank colleagues at the Department of Microbiology and Infection Control at Ahus for laboratory assistance. Parts of the contents have been presented in a report to the National Institute of Public Health. The sequencing service was provided by the Norwegian Sequencing Centre (www.sequencing.uio.no), a national technology platform hosted by the University of Oslo and supported by the “Functional Genomics” and “Infrastructure” programs of the Research Council of Norway and the Southeastern Regional Health Authorities.
This study received funding from Akershus University Hospital, National Institute of Public Health and Oslo Metropolitan University.
Compliance with ethical standards
The study was approved by the Data protection manager at Ahus (Project number12-042) and by the Regional Committees for Medical and Health Research Ethics (REK), South East, Norway (Project number 2012-102).
Informed consent was obtained from all participants.
Conflict of interest
The authors declare that they have no conflict of interest.
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