Loss of Biofilm Formation in an Emerging Foodborne Pathogen Enteroaggregative Escherichia coli (EAEC) Under Acid Stress

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.