Competition among Escherichia coli Strains for Space and Resources

Abstract

Shiga toxin-producing Escherichia coli (STEC) are a subgroup of E. coli causing human diseases. Methods to control STEC in livestock and humans are limited. These and other emerging pathogens are a global concern and novel mitigation strategies are required. Habitats populated by bacteria are subjected to competition pressures due to limited space and resources but they use various strategies to compete in natural environments. Our objective was to evaluate non-pathogenic E. coli strains isolated from cattle feces for their ability to out-compete STEC. Competitive fitness of non-pathogenic E. coli against STEC were assessed in competitions using liquid, agar, and nutrient limiting assays. Winners were determined by enumeration using O-serogroup specific quantitative PCR or a semi-quantitative grading. Initial liquid competitions identified two strong non-pathogenic competitors (O103F and O26E) capable of eliminating various STEC including O157 and O111. The strain O103F was dominant across permeable physical barriers for all tested E. coli and STEC strains indicating the diffusion of antimicrobial molecules. In direct contact and even with temporal disadvantages, O103F out-competed STEC O157E. The results suggest that O103F or the diffusible molecule(s) it produces have a potential to be used as an alternative STEC mitigation strategy, either in medicine or the food industry.

Properties of an Antimicrobial Molecule Produced by an Escherichia coli Champion

“…Additionally, the cell density was greater in SPENT than in AMMO and the difference in cell density between them increased over time. Furthermore, our data are demonstrate that SPENT did not inhibit O103F growth, further confirming our previous results [26], and, in fact, O103F grown in SPENT had a higher cell density than O103F grown in AMMO. Feasibly, O103F has a metabolic advantage and is able to utilize nutrients not used by O157A as the metabolic pathways of different E. coli strains have been shown to vary in their ability to utilize different carbon sources [30].…”

“…O157A succumbs to at least one AMMO produced by O103F, suggesting a lack of resistance. In contrast and in accordance with our previous results [26], O103F is not inhibited by any antimicrobial produced by O157A, suggesting O103F is resistant to any antimicrobials produced by O157A. Resistance to colicins and microcins can occur through the production of these antimicrobials since production is always paired with the synthesis of resistance proteins or through mutations in receptors or uptake mechanisms for the bacteriocin [34].…”

“…A previous study in our laboratory showed a diverse STEC growth inhibition by AMMO produced by O103F [26], and the results from this study strongly suggest that O103F produces at least one very effective microcin. Microcins are considered part of the killing repertoire of the probiotic E. coli Nissle strain.…”

“…A previous study in our laboratory [26] revealed a competitive O103F champion producing strong diffusible molecule (AMMO), which inhibited the growth of a wide range of STEC isolates, including a STEC runner-up (O157A). Here we isolated and further investigated the AMMO, properties.…”

Bacteriocin Occurrence and Activity in Escherichia coli Isolated from Bovines and Wastewater

“…Producers are protected from self-killing by co-synthesizing a specific immunity protein which protects against the action of the bacteriocin through various mechanisms. Some E. coli solely produce the immunity factor to gain a competitive advantage against producers [5]. Colicins and microcins intrude into susceptible E. coli by exploiting conserved transport (i.e., frequently iron uptake systems [6]), diffusion, or efflux systems as specific receptors.…”