Detection and isolation of Escherichia coli with a coding gene for enteroaggregative Escherichia coli heat-stable enterotoxin 1 from food and comparison with fecal isolates.
Enteroaggregative Escherichia coli heat-stable enterotoxin 1 (EAST1) was originally regarded as a putative enterotoxin of enteroaggregative Escherichia coli. Although its etiological role has not yet been elucidated, it has been epidemiologically suggested that some strains of E. coli possessing EAST1-coding gene (astA) but no other identifiable pathogenic properties comprise a new group of diarrhea-associated E. coli (EAST1EC). However, the source of the organisms and their prevalence in foods are still obscure. In this study, methods for detection of the organisms in foods heavily contaminated with coliforms were evaluated and properties of the isolated strains were compared with those of fecal strains. Four enrichment methods (brilliant green lactose bile broth, E. coli, lauryl tryptose broth, and a combination of brain heart infusion broth and tryptone phosphate broth) were evaluated through inspection of 115 samples. PCR showed positive results in 26 samples after enrichment with a combination of brain heart infusion broth and tryptone phosphate broth, and EAST1EC was successfully isolated from 18 samples. Fifteen samples showed a positive reaction in the PCR test after enrichment by the other methods, and the organisms were isolated from only 10 specimens. The highest prevalence of EAST1EC was found in animal products (16 of 54, 29.6%); the organism was rarely found in foods of plant origin (2 of 45, 4.4%) or fishery products (1 of 16, 6.3%). Although EAST1EC is unexpectedly common in animal products, its potential as a human pathogen remains uncertain because the possession of some virulence properties differs significantly between strains from fecal specimens and those from foods. Some food isolates, however, possess the same characteristics as diarrheal isolates do. It is necessary to clarify the pathogenicity of EAST1EC and the significance of food as a source of infection.
Toshima
Hirono
H
Department of Food and Human Health Sciences, Graduate School of Human Life Science, Osaka City University, 558-8585, Japan.
Uenaka
Eiko
E
Bi
Ying
Y
Nakamura
Hiromi
H
Ogasawara
Jun
J
Hase
Atsushi
A
Kamata
Yoichi
Y
Nishikawa
Yoshikazu
Y
D000818:Animals; D001427:Bacterial Toxins / Q000235:genetics* / Q000302:isolation & purification*; D001483:Base Sequence; D004768:Enterotoxins / Q000235:genetics* / Q000302:isolation & purification*; D004926:Escherichia coli / Q000235:genetics* / Q000302:isolation & purification*; D004927:Escherichia coli Infections / Q000209:etiology; D029968:Escherichia coli Proteins; D005243:Feces / Q000382:microbiology*; D005506:Food Contamination / Q000032:analysis*; D005516:Food Microbiology; D006801:Humans; D008460:Meat / Q000382:microbiology*; D016133:Polymerase Chain Reaction; D015995:Prevalence
D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; C034151:heat stable toxin (E coli)