Synergistic bactericidal effects of acrinol and tetracycline against Pseudomonas aeruginosa

Abstract

Combined treatment of acrinol (Ac) and tetracycline hydrochloride (Tc) against Pseudomonas aeruginosa strains isolated from clinical specimens synergistically increased the bactericidal effect. The minimum bactericidal concentration (MBC) of Ac against P. aeruginosa strain no. 985 was 200 μg/ml, while the MBC of Ac against strains no. 47 and no. 783 was above 800 μg/ml for each. The MBC of Tc was above 400 μg/ml against each of the tested strains. However, simultaneous treatment with 25 μg/ml Ac and 200 μg/ml Tc against P. aeruginosa strain no. 985 decreased the viable cell number from 10⁷ cfu/ml to <10 cfu/ml within 24 h, while a higher concentration of Tc (400 μg/ml) with Ac (25 μg/ml) reduced the viable cell number to <10 cfu/ml within 8 h. A similar synergistic bactericidal effct of Ac and Tc was observed in strains no. 47 and no. 783 by treatment with 200 μg/ml Ac and 200 μg/ml or 400 μg/ml Tc. The degree of bactericidal effect against P. aeruginosa was proportional to the concentration of Tc under the condition of a constant concentration of Ac. Furthermore, Ac-treated cells of strain no. 47 were killed by a following Tc treatment, but cells pretreated with Tc did not show such a sensitivity to Ac. To induce the synergistic effect of Ac and Tc, Ac must be applied to P. aeruginosa before or at the same time as Tc.