Implications of stx loss for clinical diagnostics of Shiga toxin-producing Escherichia coli

Abstract

Your article is protected by copyright and all rights are held exclusively by Springer-Verlag GmbH Germany, part of Springer Nature. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com". AbstractThe 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 BShiga 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.

Inconsistent PCR detection of Shiga toxin-producing Escherichia coli: Insights from whole genome sequence analyses

“…In addition, the presence of multiple fragments of stx-coding phages may be related to the loss of phages by sub-cultivation, which has already been demonstrated [15,16,38,51]. Based on our results, we would agree with Senthakumaran et al [38] who concluded that STEC with intact prophages may be uncommon and difficult to detect. Also, using WGS these authors observed the existence of a stx-negative "in vivo" strain O145:H28 with characteristics similar to another STEC strain of the same serotype [38].…”

“…Environments with a high bacterial density promote transfer of phages, with phages being both gained and lost by bacterial members within this dynamic environment [50]. In addition, the presence of multiple fragments of stx-coding phages may be related to the loss of phages by sub-cultivation, which has already been demonstrated [15,16,38,51]. Based on our results, we would agree with Senthakumaran et al [38] who concluded that STEC with intact prophages may be uncommon and difficult to detect.…”

“…Possibly, amplification of a free stx-encoding phage may have occurred at initial isolation as the two Citrobacter isolated in the present study did not have stx-encoding phage fragments in their genomes. Other PCR-based studies of E. coli have also either detected free stx-encoding phages or hypothesized the loss of stx after sub-cultivation [13,16,38]. Free stx-phages have been found in Citrobacter spp.…”

Investigation of the Causes of Shigatoxigenic Escherichia coli PCR Positive and Culture Negative Samples

“…In this study, it was possible to detect two samples with free Stx phage particles (3.8% of PCR-positive/culture-negative samples) in CFS but with the use of PMA-qPCR it was also possible to identify dead cells in the samples, together with free Stx particles and inducible Stx phages in two samples (3.8%) and in eight samples with inducible Stx phages (15.1%) (Figure 2b), further demonstrating the differing causes for culture negative samples. The stx1 and stx2 genes are mobile virulence factors, located on the genome of temperate bacteriophages [46][47][48][49] which are able to integrate in the E.coli genome during lysogeny, resulting in The stx1 and stx2 genes are mobile virulence factors, located on the genome of temperate bacteriophages [46][47][48][49] which are able to integrate in the E.coli genome during lysogeny, resulting in acquired ability to express the Shiga toxin [29]; however, the prophages can be induced to enter the lytic cycle producing toxin and new phage particles [50]. In this study, mitomycin C was used for the lytic cycle induction in the enriched samples resulting in an increase of number of positive samples for the plaque assay (Table 2, 35 samples).…”

Prevalence and Epidemiology of Non-O157 Escherichia coli Serogroups O26, O103, O111, and O145 and Shiga Toxin Gene Carriage in Scottish Cattle, 2014–2015

“…Where reservoirs of stxencoding bacteriophage coincide with receptive serogroup backgrounds, there exists the potential for evolution of emergent STEC strains. In particular, O26 stx status is known to be dynamic, with loss and acquisition of stx phage demonstrated in vitro and in vivo(53)(54)(55)(56). Individual pat samples from two herds in our study yielded both stx-negative and positive O26 isolates, suggesting that either the source animal wason March 21, 2021 by guest http://aem.asm.org/ Downloaded from colonised by two differing O26 strains, or by the same strain from which stx genes had been lost or acquired within the gut, or during laboratory culture.…”