In vitro antibacterial and antibiofilm activities of chlorogenic acid against clinical isolates of Stenotrophomonas maltophilia including the trimethoprim/sulfamethoxazole resistant strain

Abstract

The in vitro antibacterial and antibiofilm activity of chlorogenic acid against clinical isolates of Stenotrophomonas maltophilia was investigated through disk diffusion, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), time-kill and biofilm assays. A total of 9 clinical S. maltophilia isolates including one isolate resistant to trimethoprim/sulfamethoxazole (TMP/SMX) were tested. The inhibition zone sizes for the isolates ranged from 17 to 29 mm, while the MIC and MBC values ranged from 8 to 16 μg mL(-1) and 16 to 32 μg mL(-1). Chlorogenic acid appeared to be strongly bactericidal at 4x MIC, with a 2-log reduction in viable bacteria at 10 h. In vitro antibiofilm testing showed a 4-fold reduction in biofilm viability at 4x MIC compared to 1x MIC values (0.085 < 0.397 A 490 nm) of chlorogenic acid. The data from this study support the notion that the chlorogenic acid has promising in vitro antibacterial and antibiofilm activities against S. maltophilia.

Figure 1

Effect of chlorogenic acid (32 mg mL⁻¹) applied to a blank filter paper disk on MHA plate inoculated with S. maltophilia ATCC 13637. Caffeic acid which is an ester of chlorogenic acid also showed similar zone size. CF:caffeic acid, CH:chlorogenic acid, TMP/SMX:trimethoprim/sulfamethoxazole (30 μg), and DMSO:dimethyl sulfoxide (10%).

Figure 2

Effect of chlorogenic acid on the viability of S. maltophilia ATCC 13637 in liquid medium (time-kill curve). S. maltophilia ATCC 13637 grown at 37°C in the presence of chlorogenic acid at concentrations of 0 (♦), 4 (■), 8 (▲), 16 (×), and 32 (●) μg mL⁻¹ (1/2x, 1x, 2x and 4x MIC) with control (0 MIC). MIC: minimal inhibitory concentration; CFU: colony-forming units.

Figure 3

Effect of chlorogenic acid on biofilm viability of S. maltophilia ATCC 13637 at concentrations of 8, 16, and 32 μg mL⁻¹ (1x, 2x, and 4x MIC) with control (0 MIC). Comparison of absorbance between control and treated samples at 490 nm by XTT assay. XTT, 2,3-bis(2-methoxy-4-nitro-5-sulfo-phenyl)-2H-tetrazolium-5-carboxanilide; MIC: minimal inhibitory concentration.