Tipos de difusión de aire.

Antioxidant and Antimicrobial Activity 153

6.3 RESULTS AND DISCUSSION

The acetone extract of O. aurantiaca showed moderate antibacte-rial (inhibition zone diameter between 10 and 15 mm) potency against all gram-negative bacteria and no activity against S. aureus. The ethanol extract was not inhibitory against E. coli, S. flexneri, B. subtilis, and K.

pneumoniae. Although both extracts showed strong antifungal activity against C. glabrata, yet none was inhibitory against C. krusei.

6.3.3 ANTIOXIDANT ASSAYS

The concentration necessary to obtain 50% scavenging activity (IC₅₀) is presented in Table 6.2. The lower was the IC₅₀ value, the larger was the scavenging activity [12].

6.3.3.1 DPPH Activity

The results of the DPPH (Figure 6.1) assay revealed that the scavenging activity of the acetone extract was greater than that of the ethanol extract and did not differ significantly from those of rutin and vitamin C.

TABLE 6.2 The IC₅₀ Values O. aurantiaca Extracts

Reducing power DPPH ABTS

Acetone 0.21 0.12 0.10

BHT ND ** 0.05

Ethanol 0.05 0.15 0.04

Gallic acid ND ** 0.16

Rutin 0.06 0.11 ND

Vitamin C 0.12 0.10 ND

ND = Not determined; ** = No data.

against S. sonnei and S. pyogenes and the acetone extract against E. fae-calis. The ethanol and acetone extracts showed strong antifungal activity against C. glabrata with zones of inhibition of 20 ± 1.1 mm and 20 ± 1.7 mm, respectively

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FIGURE 6.1 DPPH activity of O. aurantiaca extracts.

6.3.3.2 ABTS Scavenging Activity

The ABTS scavenging activity of the ethanol extract of O. aurantiaca was higher than that of the acetone extract, BHT, and gallic acid at all concen-trations tested; and that of the acetone extract was greater than that of Gal-lic acid for extract concentrations higher than 0.05 mg/mL (Figure 6.2).

6.3.3.3 Reducing Power Assay

Reducing ability of the ethanol extract of O. aurantiaca was higher than that of rutin at concentrations lower than 0.15 mg/mL; and that of the ace-tone extract was lower than both controls at all concentrations (Figure 6.3).

In skin and soft tissue infections, S. pyogenes is one of the common-est bacterial agents that cause infections in wounds, carbuncles, impe-tigo furuncles, erysipelas, and abscesses. Many enterococcus species have been identified; however, only Enterococcus faecium and E. faeca-lis account for the greater share of human infections [6].In the past, C.

glabrata was assumed to be a nonpathogenic organism in humans, espe-cially in the mucosal tissues. However, with the recent increased use of

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immunosuppressive agents, both systemic and mucosal infections caused by C. glabrata have increased significantly, especially in AIDS patients [5]. Opuntia contains a range of phytochemicals such as gallic acid, vanil-lic acid, and catechins in variable quantities that may have biological

FIGURE 6.2 ABTS activity of O. aurantiaca extracts.

FIGURE 6.3 Reducing power of O. aurantiaca extracts.

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Antioxidant and Antimicrobial Activity 157

activity [9]. The high sensitivity shown by S. sonnei, S. pyogenes, E. fae-calis, and C. glabrata toward both extracts of O. aurantiaca may partially validate the local use of O. aurantiaca in traditional medicine against skin ailments.

S. aureus, E. coli, and C. krusei showed low sensitivity to the extracts of O. aurantiaca. Staphylococci infect wounds and are mainly responsible for abscesses, furuncles, erysipelas, carbuncles, and impetigo [9]. E. coli, which inhabits the intestines, may cause infections in wounds and sepsis.

In one study, E. coli, C. albicans, and S. aureus were reported as the most common skin pathogens [7]. The fungus C. krusei, may occur in mucous membranes and on the skin without causing any infection if present at low frequency. However, they may become pathogenic and cause candidiasis and impetigo if they overgrow the normal flora, especially in diabetics and in individuals with suppressed immune systems [7].

As free radicals are definitely implicated in the pathogenesis of skin diseases, the antioxidant capacities of O. aurantiaca were also studied.

ROS are usually produced in low quantities in aerobic organisms. When these species are released uncontrolled, they alter apoptotic pathways [1], and this may result in cutaneous malignancy. Although living cells have many antioxidant mechanisms that inactivate ROS to maintain homeosta-sis, yet unfortunately, these homeostatic mechanisms are sometimes over-burdened, and the resultant increase in cutaneous ROS may accelerate the development of cutaneous disorders.

Hence, the availability of plant-derived antioxidants is gaining much importance since past few decades. In this chapter, the antioxidant capac-ity of O. aurantiaca was investigated using DPPH, reducing power, and ABTS radical scavenging assays. The DPPH scavenging activity of the acetone extract was significant, with IC₅₀ value close to the scavenging activity of rutin and the ABTS; further, reducing power of the ethanol extract was comparable to those of the standard controls (BHT and rutin).

The ability of these extracts to scavenge DPPH and ABTS free radicals suggest that they might donate electrons that combine with radicals, mak-ing them stable and thus terminatmak-ing the radical chain reactions. The pro-found antioxidant activity of O. aurantiaca extracts is most likely due to polyphenolic compounds that are known to be present in the Opuntia genus. Although the antioxidant activity of O. aurantiaca has not been

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reported in literature, yet other species within the Opuntia genus such as Opuntia ficus-indica var. saboten extract exhibited concentration-depen-dent scavenging activity, superoxide anions, DPPH radicals, and hydroxyl radicals on different assay systems [9].