COMPARATIVE ACTIVITIES OF NEW FLUOROQUINOLONES, ALONE OR IN COMBINATION WITH AMOXICILLIN, TRIMETHOPRIM-SULFAMETHOXAZOLE, OR RIFAMPIN, AGAINST INTRACELLULAR LISTERIA-MONOCYTOGENES

We studied the activities of the new fluoroquinolones clinafloxacin, l evofloxacin, ofloxacin, and sparfloxacin alone or in combination on th e intracellular growth of Listeria monocytogenes. Against intracellula r growth of the four strains tested, a similar reduction of the bacter ial count was obtained with clinafloxacin at the dose of 10 x MIC (Del ta log(10) CFU/ml = -2.19 +/- 0.24), with levofloxacin at 8 x MIC (Del ta log(10) CFU/ml = -2.28 +/- 0.25), and with sparfloxacin at 4 x MIC (Delta log(10) CFU/ml = -2.16 +/- 0.21) after 24 h of incubation, The combination of the quinolones with trimethoprim-sulfamethoxazole or am oxicillin did not show a substantial increase in activity compared to the fluoroquinolone alone, Antagonism with rifampin was strongly sugge sted, No modification of the MIC was observed after 20 successive infe ctions of HeLa cells and contact with subinhibitory concentrations of clinafloxacin, levofloxacin, and sparfloxacin for 24 h, We conclude th at clinafloxacin, levofloxacin, or sparfloxacin could represent a ther apeutic alternative to amoxicillin for the treatment of Listeria infec tions in adults, especially clinafloxacin. whose MIC is low (0.06 to 0 .12 mu g/ml), and whose best activity against intracellular L. monocyt ogenes was obtained at a concentration of 1.2 mu g/ml, which is simila r to clinically achievable levels, The results must be confirmed in an experimental model.