Validation of a noninvasive, real-time imaging technology using bioluminescent Escherichia coli in the neutropenic mouse thigh model of infection

A noninvasive, real-time detection technology was validated for qualitative and quantitative antimicrobial treatment applications. The lax gene cluste r of Photorhabdus luminescens was introduced into an Escherichia coli clini cal isolate, EC14, on a multicopy plasmid. This bioluminescent reporter bac terium was used to study antimicrobial effects in vitro and in vivo, using the neutropenic-mouse thigh model of infection. Bioluminescence was monitor ed and measured in vitro and in vivo with an intensified charge-coupled dev ice (ICCD) camera system, and these results were compared to viable-cell de terminations made using conventional plate counting methods. Statistical an alysis demonstrated that in the presence or absence of antimicrobial agents (ceftazidime, tetracycline, or ciprofloxacin), a strong correlation existe d between bioluminescence levels and viable cell counts in vitro and in viv o. Evaluation of antimicrobial agents in vivo could be reliably performed w ith either method, as each was a sound indicator of therapeutic success. Do se-dependent responses could also be, detected in the neutropenic-mouse thi gh model by using either bioluminescence or viable-cell counts as a marker. In addition, the ICCD technology was examined for the benefits of repeated ly monitoring the same animal during treatment studies. The ability to repe atedly measure the same animals reduced variability within the treatment ex periments and allowed equal or greater confidence in determining treatment efficacy. This technology could reduce the number of animals used during su ch studies and has applications for the evaluation of test compounds during drug discovery.