The expected rise in world population and variability of climate change cause biotic and abiotic stress conditions that add uncertainty and complexity to food security and agro-industries. Plants are physiologically, biochemically, and molecularly affected when exposed to stressful conditions. Endophytic microbes that inhabit internal plant tissues without causing tissue damage or disease symptoms play a prominent role in the growth and development of host plants under both normal and abnormal conditions. In the current study, a pot experiment was conducted to verify that the same bacteria with multiple plant growth-promoting traits and osmotolerance were inoculated onto surface-sterilized maize seeds sown in sterile soil, re-isolated from these seedlings, and tested for their endophytic colonization to fulfill Koch’s postulate, proving their endophytic competence and persistence. The bacterial isolates were found to colonize plants at levels ranging from 4.30 to 5.26 Log₁₀ CFU g^-1, and the maximum colonization of inoculated isolates was observed in roots, followed by stems, and least in leaves. The re-isolated bacteria were compared with inoculated isolates in terms of their carbon source utilization, antibiotic sensitivity, and 16S rRNA gene sequences, thus determining which endophytic bacteria had the ability to colonize and persist at high levels in plant hosts by experimentally inoculating plants.