Modeling inter- and intraspecific interaction of microorganisms in a batch culture experiment

Abstract

Aim. To demonstrate the possibility of using a batch culture model to study the interaction of Salmonella Enteritidis and Salmonell Typhimurium, which are currently the leading serotypes in the etiology of salmonellosis, in an in vitro experiment both among themselves and in combination with Yersinia pseudotuberculosis and Shigella flexneri.Materials and methods. An experimental model of microorganism associations in vitro was created by co-cultivation of different microorganism strains in an LB broth. The Salmonella and Yersinia pseudotuberculosis stains stored in the museum of G.P. Somov Research Institute of Epidemiology and Microbiology at a temperature of –80 °C were used. The behavior of the associations under study was monitored for 24 h at 37 °C on a shaker. As a control, the growth curves of all the strains in monoculture were studied. The first research stage involved culturing S. Enteritidis and S. Typhimurium followed by addition of Yersinia pseudotuberculosis and Shigella flexneri strains (reference strain ATCC 12022) at the second stage.Results. In the control experiment, the growth of the tested cultures was quite similar. However, when grown in associations, S. Typhimurium outgrew S. Enteritidis. A similar study conducted with three pathogens also revealed that, when grown in monoculture, the stains exhibit no significant differences in the growth rates. However, when grown in associations, the growth of Y. pseudotuberculosis is significantly suppressed from the onset of observation during the first hour. Under these conditions, S. Enteritidis takes the dominant position.Conclusion. Our results demonstrate that batch culture can be used to study the interaction between different types of microorganisms, as well as their intraspecific relationships. We assume that the observed behavior of microorganisms can be explained, to a certain extent, by Gause’s law of competitive exclusion. This principle implies that two species competing for the same limited food source cannot coexist in one ecological niche.