The aim of this study was to examine the potential of using a lax-tagged Cronobacter sakazakii strain to monitor growth of the bacterium in various liquids. C. sakazakii was transformed with plasmid p I 6Slux. and integration of the plasmid at the desired site on the chromosome was confirmed by PCR. The growth of the lax-tagged strain was similar to that of the non ha-tagged strain, and the integrated plasmid was stable when cells were cultured in the absence of antibiotic. Growth of the lax-tagged strain was monitored in real time in Luria-Bertani broth, skim milk, and infant milk formula by using both the Luminoskan luminometer and the Xenogen IVIS imager. Bioluminescence could be detected when the lax-tagged strain was cocultured with other bacteria. The effect of monocaprylin and nisin on the growth of C. sakazakii in milk was monitored by measuring bioluminescence. In conclusion, growth of a lax-tagged C. sakazakii can be monitored in real time in both clear and opaque liquids by measuring bioluminescence. lax-tagged C. sakazakii strains could be potentially used in high-throughput assays to monitor the effects of various infant milk formula compositions on growth of the bacterium.