I am not an expert in this field, but I am very interested and have researched to find an answer. I received some assistance from tlooto.com for this response. Could you please review the response below to see if it is correct?

To successfully transfer mCherry and EGFP plasmids to Salmonella Infantis via electroporation, optimize key parameters: ensure the cells are highly competent and freshly prepared. Use pure plasmid DNA at the correct concentration. Pre-chill electroporation cuvettes and cells to improve efficiency. After electroporation, incubate the cells in SOC medium for at least 1 hour to allow recovery before plating on selective media. Verify that the antibiotic selection markers are effective and ensure the plasmid's origin of replication is compatible with Salmonella Infantis [1][2][3]. Adjusting these steps should increase your chances of successful transformation.

Reference

[1] Binotto, J., Maclachlan, P., & Sanderson, K. (1991). Electrotransformation in Salmonella typhimurium LT2.. Canadian journal of microbiology, 37 6, 474-7 .

[2] Cohen, E., Rahav, G., & Gal-Mor, O. (2020). Genome Sequence of an Emerging Salmonella enterica Serovar Infantis and Genomic Comparison with Other S. Infantis Strains. Genome Biology and Evolution, 12, 223 - 228.

[3] Baird, R., Anderson, N. J., & Bloch, J. (1981). Salmonella vertebral osteomyelitis: a complication of salmonella aortitis.. Orthopedics, 4 10, 1127-33 .

Does your strain of S. infantis express the SinI restriction endonuclease? If it does and your DNA is not properly methylated, then it may be destroyed by that nuclease. The recognition site for SinI is GGWCC, (GGACC or GGTCC), so you should also check your plasmid sequences for occurrences of these recognition sites.