Novel Cytoplasmic Bacteriocin Compounds Derived from Staphylococcus epidermidis Selectively Kill Staphylococcus aureus, Including Methicillin-Resistant Staphylococcus aureus (MRSA)

Abstract

Staphylococcus aureus (S. aureus) is one of the well-known agents causing atopic dermatitis (AD) in susceptible individuals, and Staphylococcus epidermidis (S. epidermidis) produces class I thermostable bacteriocins that can selectively kill S. aureus, suggesting protective roles against AD. There is a large need for developing precise therapies only to target S. aureus and not to harm the beneficial microbiome. On the agar well diffusion assay, live planktonic S. epidermidis showed clear zones of inhibition of S. aureus growth, but heat-killed cells and cell-free supernatants did not show this. These results would lead us to hypothesize that cytoplasmic bacteriocin from S. epidermidis will be a promising agent to inhibit S. aureus growth. Therefore, we have extracted a novel thermolabile cytoplasmic bacteriocin from S. epidermidis using trichloroactic acid (TCA)/acetone precipitation method after cell lysis with a SDS-containing buffer. These bacteriocin selectively exhibited antimicrobial activity against S. aureus and methicillin-resistance Staphylococcus aureus (MRSA), presenting no active actions against S. epidermidis, E. coli, and Salmonella Typhimurium. The extracted cytoplasmic bacteriocin compounds revealed several diffuse bands of approximately 40-70 kDa by SDS-PAGE. These findings suggest that these cytoplasmic bacteriocin compounds would be a great potential means for S. aureus growth inhibition and topical AD treatment.

Keywords: Staphylococcus aureus; Staphylococcus epidermidis; TCA/acetone precipitation method; bacteriocin.

Figure 1

The planktonic S. epidermidis ATCC12228 (SE) showed antimicrobial activity against S. aureus ATCC 25923 on the agar well diffusion assay but heat-killed S. epidermidis (A) and cell-free supernatant (CFS) (B) from S. epidermidis did not show any activities.

Figure 2

The effect of culture medium pH on the production of the cytoplasmic bacteriocin compounds. The inhibition zone of intra-cytoplasmic protein (IP) from S. epidermidis ATCC12228 at pH 5.0 or 6.0 was more prominent than pH 7.4 against S. aureus or methicillin-resistant S. aureus (MRSA). No antimicrobial activity was observed in the CFS with the overnight growth of S. epidermidis.

Figure 3

The antimicrobial activities of the intra-cytoplasmic protein (IP) from S. epidermidis ATCC12228 (SE 28) or NCCP14768 (SE 68) against S. aureus or MRSA. The antimicrobial activity was found to be stable after heating at 45 °C for 20 min but lost its actions heating to 100 °C for 20 min.

Figure 4

On the agar well inhibition assay, the concentration of cytoplasmic bacteriocin compounds from S. epidermidis ATCC12228 showing from 2 mg, 1 mg, 500 μg, 250 μg, and 125 μg/ ml in each well. Antimicrobial activity decreased with decrease in its concentration. There is no antimicrobial activity of cytoplasmic bacteriocin compounds from S. epidermidis ATCC12228 at concentration of 125 μg/ ml against S. aureus ATCC25923.

Figure 5

A bacteriocin compound profiles of SDS–PAGE of S. epidermidis ATCC12228, lane M: Molecular weight marker; Lane SE 28 IP: partially purified intra-cytoplasmic protein (IP) from S. epidermidis ATCC12228.