0 ± 0.1a 4.8 ± 0.1b Ciprofloxacin 1.4 ± 0.05a 2.2 ± 0.1b The PAEs were monitored by viable count of S. aureus after 2 h exposure to concentrations equal to MIC and 2 × MIC of antimicrobials (AKBA and ciprofloxacin). Values in the same column followed by the same superscripts are significantly NSC 683864 order different from each other (P < 0.05; Student's t test). PAE, Post antibiotic effect. Time-kill kinetic studies The time-kill kinetic studies of AKBA were performed on S. aureus ATCC 29213 (Figure 1). It showed bacteriostatic
activity at all the tested concentrations. The maximum effect of AKBA was observed at 16 and 32 μg/ml exhibiting a ≈2 log10 reduction in click here the viability of S. aureus cells when compared with non treated controls (P < 0.05)
at four and eight times it’s MIC over a period of 24 h study. Figure 1 Effect of AKBA at different concentrations (8, 16 and 32 μg/ml) on the cell viabilty of S. aureus ATCC 29213. S. aureus cells without AKBA served as control. selleck chemicals llc The effect of AKBA was observed bacteriostatic at all tested concentrations when compared with non treated control (P < 0.05) over a period of 24 h study. Each time point represents the mean log10 standard deviations (±SD) of three different experiments performed in duplicate. *, P < 0.05; (Student's t test). Biofilm inhibition and reduction AKBA effectively inhibited the formation of S. aureus and S. epidermidis biofilms, with 50% biofilm inhibition concentration (MBIC50) from 16-32 μg/ml (as derived from Figure 2A) which is in the range of 4 × MIC and 8 × MIC respectively. AKBA also effectively eradicated the preformed biofilms. The
50% biofilm reduction concentration (MBRC50) ranged from 32-64 μg/ml for both the bacterial isolates (Figure 2B). Figure 2 Effect of AKBA on the biofilm formation (A) and preformed biofilm (B) by S. aureus ATCC 29213 and S. epidermidis ATCC 12228. After incubation, the biofilms were stained with crystal violet and the optical C59 mouse density of stained adherent bacteria was determined with a multidetection microplate reader at a wavelength of 595 nm (OD595). The results are expressed as average optical density readings for crystal violet assays compared to growth control. The biofilm of S. aureus and S. epidermidis were significantly inhibited (A) and reduced (B) compared with those of bacteria without AKBA (P < 0.01). Values are mean (±SD) from four independent determinations. *, P < 0.01 (Student’s t test). Effect of AKBA on membrane integrity In order to investigate the antibacterial action of AKBA on the bacterial membrane integrity, the cell suspension of S. aureus ATCC 29213 was exposed to a concentration of 64 μg/ml AKBA for 60 and 120 min followed by staining with propidium iodide (nucleic acid stain). The AKBA exposure resulted in bacterial cell membrane disruption as evident from the increased uptake of propidium iodide in comparison to the unexposed cells (P < 0.05) (Figure 3).
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