Bacillus anthracis causes
anthrax.
Ciprofloxacin is a gold standard for the treatment of
anthrax. Previously, using the non-toxin-producing ΔSterne strain of B. anthracis, we demonstrated that
linezolid was equivalent to
ciprofloxacin for reducing the total (vegetative and spore) bacterial population. With
ciprofloxacin therapy, the total population consisted of spores. With
linezolid therapy, the population consisted primarily of vegetative bacteria.
Linezolid is a
protein synthesis inhibitor, while
ciprofloxacin is not. Since toxins are produced only by vegetative B. anthracis, the effect of
linezolid and
ciprofloxacin on toxin production is of interest. The effect of simulated clinical regimens of
ciprofloxacin and
linezolid on the vegetative and spore populations and on toxin production was examined in an in vitro pharmacodynamic model over 15 days by using the toxin-producing Sterne strain of B. anthracis.
Ciprofloxacin and
linezolid reduced the total Sterne population at similar rates. With
ciprofloxacin therapy, the total Sterne population consisted of spores. With
linezolid therapy, >90% of the population was vegetative B. anthracis. With
ciprofloxacin therapy, toxin was first detectable at 3 h and remained detectable for at least 5 h. Toxin was never detected with
linezolid therapy.
Ciprofloxacin and
linezolid reduced the total Sterne population at similar rates. However, the B. anthracis population was primarily spores with
ciprofloxacin therapy and was primarily vegetative bacteria with
linezolid therapy. Toxin production was detected for at least 5 h with
ciprofloxacin therapy but was never detected with
linezolid treatment.
Linezolid may have an advantage over
ciprofloxacin for the treatment of B. anthracis
infections.