Monitoring bioluminescent Staphylococcus aureus infections in living mice using a novel luxABCDE construct

Strains of Staphylococcus aureus were transformed with plasmid DNA containi ng a Photorhabdus luminescens lux operon (luxABCDE) that was genetically mo dified to be functional in both gram-positive and gram-negative bacteria. S . aureus cells containing this novel lux construct, downstream of an approp riate promoter sequence, are highly bioluminescent, allowing the detection of fewer than 100 CFU in vitro (direct detection of exponentially dividing cells in liquid culture). Furthermore, these bacteria produce light stably at 37 degrees C and do not require exogenous aldehyde substrate, thus allow ing S. aureus infections in living animals to be monitored by bioluminescen ce, Two strains of S, aureus 8325-4 that produce high levels of constitutiv e bioluminescence were injected into the thigh muscles of mice, and the ani mals were then either treated with the antibiotic amoxicillin or left untre ated. Bioluminescence from bacteria present in the thighs of the mice was m onitored in vivo over a period of 24 h. The effectiveness of the antibiotic in the treated animals could be measured by a decrease in the light signal , At 8 h, the infection in both groups of treated animals had begun to clea r, as judged by a decrease in bioluminescence, and by 24 h no light signal could be detected, In contrast, both groups of untreated mice had strong bi oluminescent signals at 24 h. Quantification of CFU from bacteria extracted from the thigh muscles of the mice correlated well with the bioluminescenc e data, This paper shows for the first time that bioluminescence offers a m ethod for monitoring S. aureus infections in vivo that is sensitive and non invasive and requires fewer animals than conventional methodologies.