Abstract:
Bacteriocins offer an advantage over antibiotics in that they target very specific
organisms and they are generally regarded as safe for humans. The aim of this study was
to isolate and identify bacteriocin-producing Bacillus species from Rastrineobola
argentea (Omena) and to screen their bacteriocins for their potential as antimicrobial
agents against bovine mastitis pathogens.
A total of 300 R. argentea samples were randomly purchased from retailers in Gikomba
market-Nairobi. To identify isolated bacteria, colonies were assessed using
morphological, biochemical techniques and the API KIT. Further, crude bacteriocins
produced by some of the isolates were tested for their antimicrobial activity against the
bovine mastitis pathogens Escherichia coli ATCC-25922 and Staphylococcus aureus
ATCC-25923 by well diffusion method. The physicochemical characteristics of the
crude bacteriocins produced were also assessed.
The study identified Bacillus mycoides, subtilis, pumilus and lentus as the most
predominant species. Among these, Bacillus subtilis and pumilus were found to produce
crude bacteriocins with antimicrobial activity against E. coli and S. aureus, the bovine
mastitis pathogens.
The crude bacteriocins produced were found to be fully or partially inactivated in the
presence of proteolytic enzymes like trypsin and had a lipid moiety since their activity
reduced in presence of lipase enzyme. In contrast, their antimicrobial activity was not
affected by temperature treatment of up to 100°C or in presence of ions like copper or
iron but there was slight reduction in activity with zinc ions. Their activity was optimal
at neutral and alkaline pH but reduced significantly at acidic pH.
The bacteriocins produced by these Bacillus species have desirable characteristics that
make these isolates attractive candidates with potential application for prevention of
bovine mastitis pathogens.
Keywords: Bovine mastitis pathogens, antimicrobial activity, Bacillus, bacteriocin..
