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Abstract
Purpose: Enteroaggregative Escherichia coli (EAEC) is an emerging foodborne pathogen as a significant diarrheal pathogen in multiple population groups. However, the associated phenotypic changes by which EAEC bacteria survive acid conditions, as it passes through the human digestive track, is not completely understood. Materials and methods: EAEC (T8) was grown in vitro by mimicking the in vivo pH conditions found in human stomach and intestine. Results: The lowest pH where EAEC (T8) was able to grow was pH 4.0 in Luria Bertani (LB) media, albeit with a lower growth rate and the bacteria reached log phase in approximately 7h. However, there was no significant difference in the growth pattern at mild acidic pH 5.5. In addition, EAEC (T8) grown at pH 4.0, demonstrated an absence of biofilm formation, clump or pellicle formation and umbrella shaped hemagglutination pattern and within 3h rod-shaped bacteria appeared as coccoid or spheroid forms with average dimensions approximately half the size of bacteria grown at control pH conditions. Conclusions: Taken together, our data suggest that the changes in the associated phenotypic characters might relate to the adaptation and survival of EAEC under acid stress conditions.
Highlights
Enteroaggregative E. coli (EAEC) is an important diarrheagenic E. coli, which is increasingly recognized as an emerging pathotype responsible for acute and persistent diarrhea in both developing and developed countries [1,2,3,4]
A three-stage model has been proposed for its pathogenesis: [1] characteristic stacked brick-like aggregative adherence (AA) to the intestinal mucosa, Human Epithelial Pharyngeal Cell Line (HEp-2) cells mediated by 60 MDa plasmid, encoding aggregative adherence fimbriae (AAF) for AA phenotype [7,8,9], hemagglutination (HA) of human erythrocytes, clump and biofilm formation [10,11,12], [2] increased production and deposition of mucus biofilm, which leads to mucoid stools, malnutrition and persistent colonization [13] and [3] induction of mucosal inflammation with cytokine release, mucosal toxicity and intestinal fluid secretion by enterotoxins and cause destruction of enterocytes [14,15,16,17,18]
We demonstrate that the arginine and lysine supplements in Minimal media (M9) media did not significantly alter the growth rate and Enteroaggregative Escherichia coli (EAEC) (T8) was able to grow up to pH 4.5
Summary
Enteroaggregative E. coli (EAEC) is an important diarrheagenic E. coli, which is increasingly recognized as an emerging pathotype responsible for acute and persistent diarrhea in both developing and developed countries [1,2,3,4]. Before colonizing the epithelial cells of the intestine, these bacteria pass through the acidic environment of the stomach where the luminal pH is in the range of 1.5-3.5 [20]. Once ingested, these pathogens endure a variety of exposures (acids) in the intestine by colonic microflora. The physiologically triggered pHhomeostasis mechanisms include the use of H+ antiport system to maintain internal pH (pHi) at a relatively constant level (pH ~7.6) over
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