Long-term shedding and clonal turnover of enterohemorrhagic Escherichia coli O157 in diarrheal diseases

Abstract

To investigate the length of time that Shiga-like toxin-producing Escherichia coli O157 is excreted after the onset of diarrhea, 456 serial stool specimens were obtained from 53 children. E. coli O157 cells were identified by the use of DNA probes followed by agglutination with a specific antiserum. Specimens were collected until three consecutive stool samples (collected within 9 days) were negative for E. coli O157. The median durations of shedding were 13 days (range, 2 to 62 days) in patients with diarrhea or hemorrhagic colitis and 21 days (range, 5 to 124 days) in patients that developed hemolytic uremic syndrome. In 36 (68%) of the patients, only the first culture was O157 positive, and the three cultures that followed were negative. In 7 (13%) of the patients, E. coli O157 cells were shed for more than 32 days after the onset of diarrhea; these long-term shedders were clinically asymptomatic by the end of this period. In 12 patients, one or two serial O157-negative cultures, obtained up to 8 days after a positive culture, were followed by another positive culture. Comparison of the first and last E. coli O157 isolates by pulsed-field gel electrophoresis revealed that in three of the seven long-term shedders, pulsed-field gel electrophoresis types varied. In two cases, a Shiga-like toxin gene was apparently lost during infection. The observation of long-term shedding accompanied by genotypic turnover has epidemiological and diagnostic implications.

Inhibitory activity of gut bacteria against Escherichia coli O157 mediated by dietary plant metabolites

“…The incidence of reported disease caused by enterohaemorrhagic Escherichia coli (EHEC) [1] has recently escalated dramatically; the worst outbreak resulted in 20 deaths in Scotland in 1996 [2]. The rumen and colon provide sources for E. coli O157 shed in ruminant faeces [3,4] which may contaminate the human food chain, and faecal shedding is also implicated in transmission between humans [5]. Shedding of E. coli by ruminants is in£uenced by the diet [6].…”

Comparison of PCR-RFLP and PFGE for determining the clonality of enterohemorrhagicEscherichia colistrains

“…Genetic changes have been demonstrated by PFGE in EHEC strains after passage through the bovine or human gastrointestinal tract (Karch et al, 1995;Akiba et al, 1999Akiba et al, , 2000, as well as following in vitro subculturing (Tenover et al, 1995;Iguchi et al, 2002). The phenomenon has been described as 'clonal turnover' (Karch et al, 1995). The determination of clonality among EHEC strains by PFGE has therefore appeared to be somewhat confusing.…”

“…Analysis by PFGE is based on the genome diversity of the bacterial strain, which reflects genetic changes such as the gain or loss of a restriction site, and an insertion or deletion of gene fragments occurring over time (Tenover et al, 1995). However, such genetic changes have been shown to occur more quickly, at least in the case of EHEC (Karch et al, 1995;Tenover et al, 1995;Akiba et al, 1999Akiba et al, , 2000Iguchi et al, 2002).…”

“…Pulsed-field gel electrophoresis (PFGE) is a commonly used molecular typing method for identifying strains responsible for disease outbreaks and has been used for a variety of pathogens, including EHEC, because of its high resolution and reproducibility (Terajima et al, 1999Izumiya et al, 1997;Johnson et al, 1995;Terajima et al, 2000;Barrett et al, 1994;Grif et al, 1998;Karch et al, 1995). However, there are several disadvantages associated with PFGE.…”

“…However, there are several disadvantages associated with PFGE. For example, the RFLP patterns of PFGE can change, even after the passage of an EHEC strain through bovine or human gastrointestinal tracts (Akiba et al, 1999(Akiba et al, , 2000Karch et al, 1995) (N. Yoshii, unpublished data) as well as during subculturing of the EHEC strains (Tenover et al, 1995;Iguchi et al, 2002). Furthermore, it is essential for the PFGE analysis to isolate a strain.…”