जर्नल ऑफ माइक्रोबियल पैथोजेनेसिस

Caenorhabditis elegans as a simple in vivo model for combinatorial therapy with thioridazine and dicloxacillin against infections with methicillin-resistant Staphylococcus aureus

Abstract

Marianne O Poulsen

The shortage of drugs active against methicillin-resistant Staphylococcus aureus (MRSA) is a growing clinical problem. In vitro studies indicate that the phenothiazine thioridazine (TZ) might enhance the activity of the β-lactam antibiotic dicloxacillin (DCX) to a level where MRSA is killed, but positive in vivo studies have yet to be performed. We have introduced Caenorhabditis elegans infected by MRSA as an in vivo model to test the effect of TZ as a helper drug in combination with DCX. Because TZ is an anthelmintic, initial experiments were carried out to define the thresholds of toxicity, determined by larval development, and induction of stress-response markers. No measurable stress effects were observed at the concentrations below 64 mg/L TZ. Of seven tested MRSA strains the most pathogenic strain (ATCC 33591) was chosen for treatment analysis. Full-grown C. elegans were exposed to the test strain for three days and subsequently treated with 8 mg/L DCX and 8 mg/L TZ for two days. This resulted in a 14-fold reduction in the intestinal MRSA load as compared with untreated controls. Each drug alone resulted in a two to threefold reduction in MRSA load. In conclusion, we have proved C. elegans as a simple model for testing synergy between TZ and DCX against MRSA. Moreover, we have shown that TZ enhances the activity of DCX in a simple in vivo host model as C. elegans leading to a decrease of bacterial load of MRSA in the nematode gut and intestine.