Determination of anti-staphylococcal activity of thymoquinone in combinations with antibiotics by checkerboard method using EVA capmat™ as a vapor barrier

Abstract

Thymoquinone (Tq) has been reported to potentiate the in vitro growth-inhibitory activity of some antibiotics especially against Staphylococcus aureus. However, it has been shown that Tq vapors can affect the results of susceptibility testing by standard broth microdilution method. Therefore, we made a comparative experiment with and without ethylene vinyl acetate cap mats (EVA capmatä) on microplates. The results showed significant differences in the minimum inhibitory concentration values and proved this capmat as an effective vapor barrier. Therefore further experiments focused on the in vitro anti-staphylococcal combinatory effect of Tq with oxacillin, penicillin, and tetracycline against various S. aureus strains have been performed by checkerboard method using EVA capmatä. The combined effect was evaluated according to the sum of fractional inhibitory concentrations (RFIC). Synergy was obtained for combination with oxacillin against 3

Volatile Antimicrobial Agents and In Vitro Methods for Evaluating Their Activity in the Vapour Phase: A Review

“…Volatility causes a risk of active substance losses via evaporation during sample handling, experiment preparation, and incubation, depending on time and temperature conditions [40,41]. Although, in conventional assays based on disc diffusion and dilution tests, this can be prevented by using vapour barriers such as an ethylene vinyl acetate (EVA) capmat [42] and a cover glass with a plastic seal ring [43], this approach does not solve the problem of the assessment of the antimicrobial potential of VAs in a vapour phase. In this case, the interaction of VAs with the matrix onto which they are applied (e.g., paper disc, cultivation broth) is a crucial aspect affecting the speed and intensity of their evaporation into the atmosphere.…”

In vitro antagonistic inhibitory effects of palm seed crude oils and their main constituent, lauric acid, with oxacillin in Staphylococcus aureus

“…Three clinical isolates of drug resistant S. aureus (SA1, SA2, and SA3) and one epidemic MRSA strain (EMRSA-15) were obtained from the Motol University Hospital (Prague, CZ). Oxacillin, gentamicin, tetracycline, and penicillin were used as markers of the antibiotic resistance as it has been previously determined 97 – 99 . Based on the MIC values, clinical isolates were identified to be resistant to: SA1—resistant to gentamicin (MIC 8 µg/mL) and tetracycline (MIC 8 µg/mL); SA2—resistant to oxacillin (MIC 68 µg/mL), gentamicin (MIC 16 µg/mL) and tetracycline (MIC 8 µg/mL); SA3—resistant to gentamicin (MIC 8 µg/mL) and penicillin (MIC 18.67 µg/mL); EMRSA-15—resistant to oxacillin (MIC 99.56 µg/mL) and penicillin (MIC 16 µg/mL).…”

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“…The antibacterial effect synergism of N. sativa seed essential oil with antibiotic was reported in several previous studies, therefore it may be used in combination with antibiotic. 28,46 Further investigation is needed in order to investigate the cytotoxic effect of N. sativa seed o/w emulsion regarding to human use.…”