Importance of the overexpression of AcrAB efflux pumps in the low-level resistance of pathogens to antimicrobials requires a better understanding of the AcrAB regulation. The goal of the present research was to study the transcription of acrAB, as well as the genes that play a role in its regulation in Salmonella enterica serovar Typhimurium. We monitored the transcription of these genes during growth at 30 degrees C and 37 degrees C, and thoroughly studied the effect of salicylate, paraquat and decanoate. The strengths of the promoters' activities were ordered from strong to weak as micF > rob > acrAB > soxS, marRAB. At both temperatures, marRAB was mainly upregulated by salicylate and decanoate, soxS by paraquat and acrAB and micF by all three compounds. rob was always downregulated. Transcription rates of all promoters were at the greatest level at the beginning of the stationary phase and, except for soxS, levels of transcription and induction were greater at 37 degrees C. Results show that despite the promoters' similar activity and the sequence homology between Escherichia coli and S. typhimurium, regulation of the investigated genes of both strains differed in the response to temperature. This difference was found to be dependent on the promoters' sequence, as the marRAB and acrAB promoters maintained their original dependence on temperature when they were analyzed in the other strain. Hence, it is most likely that the nutrient-limited environment at 37 degrees C in the human body will lead to increased transcription of marA, acrAB and micF in Salmonella, enhancing the resistance properties of the bacteria.