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Listeria monocytogenes is a facultative intracellular bacterium that causes severe infections associated with a high mortality rate. Moxifloxacin presents extended activity against gram-positive bacteria and has recently been suggested to be a potential alternative in the treatment of listeriosis. We evaluated the in vitro efficacy of moxifloxacin against L. monocytogenes using a combination of epidemiological and experimental approaches. The median MIC of moxifloxacin for a large collection of L. monocytogenes strains of various origins (human, food, and environment) was 0.5 g/ml (MIC range, 0.064 to 1 g/ml). No differences were observed, irrespective of the origin of the strains. Moreover, no cross-resistance with fluoroquinolones was detected in strains that have been reported to be resistant to ciprofloxacin. The in vitro activities of moxifloxacin and amoxicillin were compared by time-kill curve and inhibition of intracellular growth experiments by using a model of bone marrow-derived mouse macrophages infected by L. monocytogenes EGDe. Both moxifloxacin and amoxicillin were bactericidal in broth against extracellular forms of L. monocytogenes. However, moxifloxacin acted much more rapidly, beginning to exert its effects in the first 3 h and achieving complete broth sterilization within 24 h of incubation. Moxifloxacin has a rapid bactericidal effect against intracellular reservoirs of bacteria, whereas amoxicillin is only bacteriostatic and appears to prevent cellular lysis and the subsequent bacterial spreading to adjacent cells. No resistant bacteria were selected during the in vitro experiments. Taken together, our results suggest that moxifloxacin is an interesting alternative to the reference treatment, combining rapid and bactericidal activity, even against intracellular bacteria.

The use of porphyrin derivatives in photodynamic therapy is of excellent prospect for the treatment of superficial or easily reachable tumors. The selection of porphyrin derivatives by tumor cells depends to a large extent of their ability to interact with the biological membrane. The evaluation of porphyrin interaction with phospholipids can thus be used as a screening method. In this work we report on the assessment of the interaction of three new porphyrin derivatives with various phospholipids forming Langmuir films by surface tension and surface pressure measurements, grazing incidence X-ray diffraction, and liquid chromatography on an IAM stationary phase. The results show that the hydroxylated phenylporphyrin (m-THPP) is able to interact with all studied phospholipids and to significantly disorganize the structure of their monolayers. Obviously, the interaction occurs at the level of the hydrophobic chains of a phospholipid. A triglucoconjugated phenylporphyrin (m-TPP(Glu)3) also interacts with the phospholipids though to a lesser extent. Conversely, the tetraglucoconjugated derivative (m-TPP(Glu)4) exhibits both a weak surface activity and a poor affinity for the studied phospholipids. Thus, whereas m-THPP and m-TPP(Glu)3 are expected to penetrate into a biological membrane, m-TPP(Glu)4 seems unlikely to do so.