A novel antimicrobial peptide with anti-MRSA activity

Abstract number: 1733_1581

Aunpad R., Na-Bangchang K.

Objectives: To search and characterise a new antimicrobial peptide against MRSA.

Methods: Forty-three different water and soil samples were collected from three different areas from Thailand. The single colony obtained from each sample was screened for its antagonistic activity against the indicator strain, methicillin resistant Staphylococcus aureus (MRSA) by co-culture method. The agar-well diffusion method was used to assess the antimicrobial activity spectrum of 20 selected bacterial strains against 20 Gram-positive and Gram-negative test microorganisms. The agent containing antimicrobial peptide (ACAP) prepared from the culture supernatant of one strain, WAPB4, was tested for its antimicrobial spectrum, enzyme sensitivity, heat and pH stability and mode of action. The antimicrobial peptide was purified from ACAP by a three-step procedure: solvent extraction, solid phase extraction and followed by reversed phase chromatography. The molecular mass was determined by mass spectrometry.

Results: A total of 20 water and soil isolated bacteria can inhibit the growth of MRSA. It was also found that three Gram-positive isolated bacteria strain WARY9–1, WARY6–6 and WASM9–25 showed a broad range of inhibition. Two Gram-negative bacteria strain WARY9–10 and WARY7–4 are active against both Gram-positive and Gram-negative bacteria. One strain, WAPB4, identified as Bacillus pumilus showed remarkable antibacterial activity against MRSA and VRE. The antimicrobial peptide produced by WAPB4 was heat stable up to 121°C, 15 min and active within the pH range of 3–9. Its activity disappeared when treated with pronase E, chymotrypsin and trypsin demonstrating its proteinaceous nature. ACAP showed bacteriostatic effect to MRSA in vitro. The antimicrobial peptide could be purified by a three-step procedure and the molecular mass as determined by mass spectrometry was 1994.62 Dalton.

Conclusion:Bacillus pumilus strain WAPB4 produced a new antimicrobial peptide with broad spectrum antibacterial activity including MRSA and VRE. The compound is thermal and pH stable and has potential for use as an alternative antibacterial agent for the treatment of infection with MRSA and VRE.