Chemotherapy is often futile in systemic listeriosis, translating to being a peril to public health. There is, thus, an imperative need for novel antilisterial compounds, possibly acting through mechanisms dissimilar to those of existing drugs. The present study describes one such agent-the non-steroidal anti-inflammatory drug (NSAID) diclofenac sodium (Dc). The National Committee for Clinical Laboratory Standards (NCCLS) minimum inhibitory concentration (MIC), mode of action, and two mechanisms of action, i.e., on bacterial DNA and membrane, have been characterized with respect to Dc. The drug showed noteworthy inhibitory action (MIC90 = 50 microg/ml) against Listeria strains, demonstrated cidal (minimum bactericidal concentration [MBC]=100 microg/ml) activity, inhibited listerial DNA synthesis (45.48%; incorporation of [methyl-3H] thymidine), and possessed bacterial membrane-damaging activity (37.33%; BacLight assay). Dc could be used as a lead compound for the synthesis of new, more active agents perhaps devoid of side effects. Further, quantitative structure-activity relationship (QSAR) studies will contribute to a new generation of promising adjuvants to existing antilisterial drugs.

Spontaneous basal cell carcinoma (BCC) is very rare in rats, with an incidence rate of only 0.14% reported in aged animals. A spontaneous BCC occurred in a 7-week-old Sprague-Dawley rat housed in a specific-pathogen-free animal facility. The tumor was a single, well-delineated reddish-brown subcutaneous mass measuring 2 x 2 cm and located in the left inguinal region. Microscopically, the tumor consisted of basaloid cells in lobular and cribriform growth patterns and with a high mitotic rate. Immunohistochemically, cytokeratin 14 (an indicator for basal keratinocytes of the epidermis) showed strong reactions throughout the whole tumor, and cytokeratin 18 showed weak but positive reaction in the majority of nested tumor cells. To the authors' knowledge, this is the first report of spontaneous BCC occurrence in young Sprague-Dawley rats.