SUMMARYInternalization of herpes simplex virus type 1 (HSV) KOS strain by HEp-2 cells was reversibly inhibited by pretreatment of cells with cytochalasins B and D. Internalization of virus following preincubation at 4 °C and temperature shift to 37 °C was normally preceded by a 5 to 8 min lag period and was complete within 20 to 30 min. A similar lag period followed HSV addition at 37 °C. Cytochalasin D was fivefold more active on HSV entry than cytochalasin B, with 50~ inhibition at 2 ~tM and 10 ~tM respectively. Inhibition was completely reversible, such that all cell-bound infectious virus was recovered upon removal of cytochalasin. In conjunction with previous reports, the activity of cytochalasin on HSV entry suggests that a change in cytoskeletal structure following virus attachment triggers a microfilament activity important for internalization of HSV by HEp-2 cells.
We tested the suspeptibility of Rickettsia conorii to ciprofloxacin, a new quinolone antibiotic. A final concentration of 1 ,ug/g of egg was effective in suppressing chicken embryo lethality, and a concentration of 0.25 ,g/ml inhibited plaque formation in a plaque assay; however, a concentration of 0.5 ,ug/ml was necessary to obtain rickettsiacidal activity. These results support the idea that ciprofloxacin could be of clinical use in treating Mediterranean spotted fever.Tetracycline and chloramphenicol are the only antibiotics of clinical use in treating spotted-fever-group rickettsiosis. The purpose of this work was to evaluate the susceptibility of Rickettsia conorii to ciprofloxacin, a new quinolone antibiotic. Three methods were used: the reduction of chicken embryo lethality (5), the reduction of plaque formation (8) and, as proposed by McDade (4), the application of a filter paper disk containing antibiotics to the agar overlay for the detection of a zone of inhibition of plaque formation.MATERIALS AND METHODS Bacterial strain. R. conorii (ATCC VR 141) cultured on Vero cells (four passages) was used in this study. When dilution was necessary (plaque assay), the inoculum was diluted in Eagle minimal essential medium. The titer of the inoculum was determined by the plaque assay technique by determining the number of PFU per milliliter (6).Antibiotic. Ciprofloxacin monohydrate powder (concentration, 990 ,ug/mg, lot no. 9583 96; a gift from Bayer) was dissolved in distilled water to make a stock solution with a concentration of 1 mg/ml. The stock solution was diluted in Eagle minimal essential medium for the egg experiment and directly in the medium for the plaque assay. The filter paper disk had a 5-,ug concentration.Eggs. "Antibiotic-free" embryonated eggs were obtained from the National Institute of Agronomic Research. Thirty chicken embryos, 5 days old, were injected in the yolk sac with 0.25 ml of the antibiotic solution to obtain a final concentration of 0 (positive control), 0.25, 0.5, 1, or 2 ,ug/g of egg. At 30 min later, R. conorii was inoculated into the yolk sac in a 0.25-ml volume containing 2,500 PFU. This sequence of introducing antibiotics is generally used (5).Five chicken embryos were injected with distilled water as a negative control.In calculating the mean survival time, all embryos alive at the end of the experiment were considered to have died on day 13 (5).Plaque assay. The plaque assay procedure used in this study was essentially the same as that described earlier (6). Vero cell monolayers (24 h) in round plastic tissue culture * Corresponding author. disks (60 mm; Coming Glass Works) were infected with 1 ml of a solution containing 2,500 PFU and, after incubation (1 h at laboratory temperature), were overlaid with 5 ml of a medium containing Eagle minimal essential medium, 2% calf serum, 2% N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES), and 0.5% agar. The antibiotic stock solution was added to obtain a final concentration of 0 (positive control), 0.06, 0.125, 0.25, 0.5,...
The activity of pefloxacin against Rickettsia conorii and R. rickettsii was determined by several methods. The mean survival time of embryonated eggs infected with R. conorii was increased by pefloxacin 50 micrograms/egg; plaque formation in Vero cells was inhibited by 1 mg/l. In a microplate assay, the MIC of pefloxacin was 0.5 mg/l for R. conorii and 1 mg/l for R. rickettsii. The results support the use of pefloxacin in treating spotted fever rickettsioses.
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