Document Type : Original Article
MICROBILOGY DEPARTMENT, IRAN MEDICAL SCIENCES UNIVERSITY, TEHRAN, IRAN
Introduction: Lactic acid bacteria are widely used for the fermentation and preservation of dairy and meat products and to improve their aroma and texture. The aim of this study wasto screen Lactobacillus plantarum isolated from sausage for detection of plasmids, protein bandsand phages, to find possible linkage of bacteriocin production to genetic location.
Material and Methods: Two Lactobacillus plantarum with antibacterial activitywere isolated from sausage. Bacterial plasmids were isolated by alkali lysis and electrophoresis through agarose gel. Proteins were precipitated from cell-free supernatants by ammoniumsulphate and analysed by SDS-PAGE. For detection of phages, mitomycin C of final concentration of 2.5 óg/ml was used and phages were detected by transmission electron microscopy.
Results: One plasmid of about 4.5 kbp was detected in one Lactobacillus plantarum strain.Two bands of proteins were found on SDS-PAGE. The molecular weight of protein bands of Lacto. plantarum without plasmid was higher than the protein bands of Lacto. plantarum with plasmid. A phage was detected on the cell wall of one strain of Lacto. Plantarum; no plasmid was detected in this Lacto. plantarum. It appears that antibacterial activity is located in the phage of this strain.
Conclusion: The high molecular weight of proteins with a wide spectrum effect on bacteria may indicated chromosome-coded bacteriocin. The role of phages in lactobacilli couldbe a factor which inhibit meat product starter cultures or attributed in antimicrobial activity, i.e.antibacterial genes might be on chromosomal phages. Bacteriophages could be a threat toindustrial fermentation foods.