Abstract
Objective: The aim of the current study was to isolate and identify the strain having broad spectrum antibacterial and antibiofilm activity and characterize its antimicrobial substance.
 Methods: Lactic acid bacteria isolated from the raw milk of Indian goat species Babri and Sirohi (Capra aegagrus hircus) were screened for antibacterial activity against Staphylococcus epidermidis, Micrococccus luteus, Pseudomonas fluorescens and Escherichia coli. The selected strains were also analysed for anti-biofilm activity on S. epidermidis. The potential bacterial strain was characterized at molecular level by 16S rDNA sequencing. The antimicrobial substance produced by P. acidilactici was precipitated by 90% ammonium sulphate and subsequently ultra filtered. It was analysed for size, stability under various pH, temperature, chemicals and enzymatic conditions. Its mechanism of killing was determined by ML35p assay and scanning electron microscopy (SEM).
 Results: The 16S rDNA sequence of the potential isolate, possessing broad spectrum antibacterial activity and antibiofilm activity against S. epidermidis, was deposited to Genbank under accession no. KP671843 and was identified as Pediococcus acidilactici. The partially purified bacteriocin ran at approximately 3500 Da on tris- tricine SDS-PAGE and showed antibacterial activity against S. epidermidis by In-gel assay. Partially purified bacteriocin was stable at wide pH and high temperature and also to the treatment of lipase, amylase, catalase and various detergents/organic solvents. However, it was sensitive to proteolytic enzymes indicating its proteinaceous nature. Results of membrane permeability assay revealed that the bacteriocin targets bacterial cell membrane as its bactericidal action.
 Conclusion: The bacteriocin from P. acidilactici has the potential to be used as broad spectrum antibacterial and antibiofilm agent.
Highlights
Bacteriocins are short chain peptides which are ribosomally synthesized by bacteria and are found to be active against narrow as well as broad spectrum bacteria
Cell free supernatant (CFS) was collected by centrifuging overnight grown culture of bacterial isolates at 10,000g/ min/ 4°C. 10μl of CFS was poured in agar well and incubated at 37°C for h and zone of inhibition was measured according to the CLSI guidelines (Sharma, 2018)
The phylogenetic tree of 16S rDNA sequence of P. acidilactici strain GAM218 was constructed with other Pediococcus species using CLUSTAL W software
Summary
Bacteriocins are short chain peptides which are ribosomally synthesized by bacteria and are found to be active against narrow as well as broad spectrum bacteria. LAB are known for potential source of bacteriocinogenic bacteria as well as bacteriocin isolation but most of the bacteriocins have been poorly characterized (Alvarez-Sieiro, 2016). Bacteriocins are small peptides synthesized by bacteria including LAB which help them to protect mainly against closely related species. Bacteriocins belonging to class II are small unmodified hydrophobic peptides which are very diverse. They have been further classified as IIa having antilisterial activity and include pediocin or similar bacteriocins. The current study was undertaken to isolate the bacteria producing antimicrobial substance from goat milk of Indian goat species as it has been reported for rich source of indigenous microflora. The antimicrobial substance from selected strain was partially purified and characterized
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