Abstract

Ratchaneewan Aunpad*, Napat Sripotong, Keawta Khamlak, Siriwipa Inchidjuy, Panthip Rattanasinganchan and Duangnate Pipatsatitpong

The search for a novel peptide-based antibiotic as replacement for currently used antibiotics is promising as it seems to develop less resistant compared to that of other type of antibiotic. Eighteen different food and soil samples were used for screening of a novel bioactive peptide producing bacteria. Among 1,265 isolated bacteria, one hundred and sixty seven isolated colonies showed antibacterial activity against methicillin resistant Staphylococcus aureus (MRSA) and Listeria monocytogenes by co-culture method. The activity of partially purified bacteriocin or PPB prepared from three isolated strains, CR-1-2L, SP-1-36LM and SO-4-1LM against L. monocytogenes were 105 AU/ml, 2000 AU/ml and 1000 AU/ml, respectively. PPB from three isolated bacteria showed narrow inhibition as they are active only against gram positive bacteria. PPB produced by CR-1-2L, SP-1-36LM and SO-4-1LM was heat stable up to 100°C for 60 min and active within the pH range of 3- 9. The activity of PPB prepared from three isolated strains CR-1-2L, SP-1-36LM and SO-4-1LM disappeared when treated with proteinase K, chymotrypsin and trypsin demonstrating their proteinaceous nature. These three isolated strains can be regarded as bacteriocin producing bacteria or BAC. They were all identified as Bacillus sp. by 16S rRNA gene sequence. The effect of PPB prepared from strain SO-4-1LM was bactericidal to L. monocytogenes and the highest activity was found at six hours after incubation. Tris-Tricine SDS-PAGE analysis revealed that the bacteriocin prepared from Bacillus sp. SO-4-1LM had an apparent molecular weight of 2.5 kDa. The bioactive peptide from these three isolated bacteria has a potential for use as an alternative antibacterial agent for the treatment of infection with MRSA and/or use in the food industry in the future.