Susceptibility Assessment of Methicillin-Resistant Staphylococcus aureus Strains to Lepidium sativum Extract

Abstract

Many plant-derived compounds have been used to treat microbial infections. Staphylococcus aureus a common cause of many organ infections, has generated increasing concern due to its resistance to antibacterial drugs. This work was carried out to explore the susceptibility of 6 strains (LN872136, LN872137, LN871238, LN871239, LN872140, and LN871241) of methicillin-resistant Staphylococcus aureus to aqueous extract of Lepidium sativum seeds in vitro. Various concentrations (5-20 mg/mL) were used to evaluate the effect of the extract on bacteria growth via the assessment of the microbial biomass and the inhibition zone (IZ). The results showed that the plant extract at 15 or 20 mg/mL, significantly decreased the the biomass of S aureus strains after 24 or 48 hours exposure period. Staphylococcus aureus (LN871241) showed the largest IZ at 20 mg/mL and documented by scanning electron microscope. The current work may suggest that L sativum seed extract can be candidate as a promising antimicrobial agent to treat infection with methicillin-resistant S aureus.

Keywords: Lepidium sativum; antibacterial; methicillin-resistant S aureus; microbial biomass.

Figure 1.

Influence of Lepidium sativum extract (5-20 mg/mL) on the dry weight gain of Staphylococcus aureus (LN872136). Results are calculated as mean (SD; n = 3). *P ≤ .05 versus the control untreated strain (zero concentration) after 24 hours exposure to the natural extract, ^a P ≤ .05 and ^b P ≤ 0.01 versus the control after 48 hours exposure to the plant extract. SD indicates standard deviation.

Figure 2.

Influence of Lepidium sativum natural extract (5-20 mg/mL) on the dry weight gain of Staphylococcus aureus (LN872137). Data are calculated as mean (SD; n = 3). *P  ≤ .05 with respect to control untreated strain (zero concentration) after 24 hours exposure to the plant extract. ^a P  ≤ .05 compared with the control untreated strain after 48 hours exposure to plant extract. SD indicates standard deviation.

Figure 3.

Influence of various concentrations of Lepidium sativum on the dry weight gain of Staphylococcus aureus (LN871238). Data are calculated as mean (SD; n = 3). *P ≤ .05 compared with the control untreated strain (zero concentration) after 24 hours exposure to the plant seed extract, ^a P ≤ .05 and ^b P ≤ .01, compared with the control untreated strain after 48 hours exposure to the plant extract. SD indicates standard deviation.

Figure 4.

Influence of various concentrations of Lepidium sativum on the dry weight gain of Staphylococcus aureus (LN871239). Data are calculated as mean (SD; n = 3). Nonsignificant changes in the dry weight of the bacterial strain exposed to different concentrations of the plant extract after 24 or 48 hours compared with the control counterpart untreated strain (zero concentration). SD indicates standard deviation.

Figure 5.

Influence of various concentrations of Lepidium sativum on the dry weight of Staphylococcus aureus (LN872140). Data are calculated as mean (SD; n = 3). *P ≤ .05, **P ≤ 0.01 compared with the control (zero concentration) after 24 hours exposure to the plant extract, ^a P ≤ .05, ^b P ≤ .01, and ^c P ≤ .001 compared with the control after 48 hours exposure to the plant extract. SD indicates standard deviation.

Figure 6.

Influence of various concentrations of Lepidium sativum on the dry weight of Staphylococcus aureus (LN871241). Data are calculated as mean (SD; n = 3). *P ≤ .05 compared with the control (zero concentration) after 24 hours exposure to the plant extract, ^a P ≤ .05 and ^b P ≤ .01 compared with the control after 48 hours exposure to the plant extract. SD indicates standard deviation.

Figure 7.

Effect of Lepidium sativum extract on the growing of Staphylococcus aureus showing the IZ of the different strains. (A) IZ of S aureus (LN872136), (B) IZ of S aureus (LN872137), (C) IZ of S aureus (LN871238), (D) IZ of S aureus (LN871239), (E) IZ of S aureus (LN872140), and (F) IZ of S aureus (LN871241). IZS indicates inhibition zone.

Figure 8.

Scanning electron micrographs of Staphylococcus aureus (LN872141) bacterial cells treated with Lepidium sativum aqueous extract at 37^oC for 24 hours. A, Micrograph of untreated S aureus (LN872141) showing normal shape. B, C, Micrographs of the bacterial strain exposed to L sativum extract showing abnormal morphology, (B) showing rough of the cell wall due to wrinkles (arrows), and (C) showing separation of cell wall and a decrease in the size of the bacterial cell diameter (arrows).