Stability of pAK lux 1 in Salmonella. Salmonella strains carrying pAKlux 1 were subcultured under ampicillin selective and non-selective conditions for 15 days. At each passage, bioluminescence was measured and normalized for cell density (OD600). The ratio between the normalized values under non-selective (nLB) and ampicillin selected conditions (nLBamp) revealed the plasmid stability in different Salmonella serovars. The black line represents the mean of eleven strains, and the red line is the linear trend line.