The symbiotic bacterium <i>Serratia liquefaciens</i> enhances the development of <i>Bacillus thuringiensis</i> bacteriosis in Colorado potato beetle larvae by alkalinization of pH in the midgut

Abstarct. Invasion by pathogens is accompanied by competitive interactions between the pathogens and the microbiota, by the allocation of a niche in the intestine for the pathogen, and induction of immune processes in the host organism. These processes are accompanied by the accumulation of microbiota secondary metabolites, which may result in alterations of physicochemical characteristics of the host gut. These events may affect the speed of progression of bacterial infections, including secondary bacterial infections. In this study, experimental evidence showed that within the initial 24-h period, both in vitro and in vivo, interaction between Bacillus thuringiensis (Bt) and the symbiotic bacterium Serratia liquefaciens caused alkalization of the medium: both the culture fluid and the midgut contents of the Colorado potato beetle (CPB). Combined oral administration of S. liquefaciens and Bt resulted in 83% mortality of CPB larvae as early as 48 h after the inoculation. This mortality rate was 8.3-fold higher than that (