Minimum Inhibitory Concentration

The minimum inhibitory concentration (MIC) was then determined only against *S. aureus*. MIC tests were performed with the 7 crude extracts, obtained according to factorial design, and with some fractions separated by column chromatography. The best result for subfraction 4 (Table 2) was attributed to the higher *p*-anisic acid concentration verified by HPLC analyses. The activity of phenolic acids against *S. aureus* has been verified in several studies [50–52]. According to Basri et al. [53], the minimum inhibitory concentration (MIC) of *p*-anisic acid against *S. aureus* is MIC = 15.0.

**Table 2.** Minimal inhibitory concentration (MIC) of *A. mearnsii* crude extracts and its purified fractions against *S. aureus*.


Although the MIC of the *A. mearnsii* flower extracts obtained with supercritical fluid was high, its combination with synthetic and classic antibiotics may enhance the extract of *A. mearnsii* activity. According to studies, the synergistic effect of the association of antibiotics with plant extracts against resistant bacteria leads to new options for the treatment of

infectious diseases. [54]. For example, the extracts of *Solanum paludosum Moric* obtained by the supercritical fluid process, tested by Siqueira [55], have not presented antibacterial activity but have shown modulating activity that reduced the antibiotic MIC up to eight times. Olajuyigbe & Afolayan [56] tested the effect of the methanolic extract of *A. mearnsii* bark and its synergistic effect when combined with antibiotics against 8 bacteria of clinical relevance. Concerning *S. aureus* (ATCC 6538), the minimum inhibitory concentration of the extract was 0.313 mg·mL−<sup>1</sup> and it has presented synergism with antibiotics such as erythromycin, metronidazole, amoxicillin, chloramphenicol, and kanamycin. Thus, despite the low effect of *A. mearnsii* flower extracts, there is the potential for exploring its combined use with traditional drugs. These results also suggest future tests against other Gram-positive bacteria such as *Staphylococcus epidermidis*, one of the main causative agents of hospital infection [57].
