ABSTRACT
A direct plate bioassay procedure was applied for rapid and quantifiable assessment of the influence of various nutritional parameters on pediocin production by Pediococcus acidilactici NRRL B5627. Solid-state cultivation of the microorganism was done on MRS-based media over 3-and 6-hours incubation periods. Nutritional parameters assessed included the carbon source (glucose, sucrose, fructose, galactose, glycerol), and various salts (NH(4)PO(4), CaCl(2), KH(2)PO(4), MnSO(4).H(2)O). Glucose was found to be the optimal carbon source while glycerol exhibited the most suppressive effect. Using glucose as the carbon source, addition of various salts, in amounts used in liquid media commonly applied in the cultivation of the pediococci, was assessed with respect to bacteriocin production on a per cell basis. Experimental data obtained showed that several nutritional parameters repress pediocin production by P. acidilactici, while the direct plate assay proved to be a good pilot assay prior to conducting more intensive kinetic analysis in liquid cultivation.
Subject(s)
Bacteriocins/biosynthesis , Pediococcus/metabolism , Biological Assay , Culture Media , KineticsABSTRACT
Fermentation broths of Pediococcus acidilactici NRRL B5627 exhibited a certain antimicrobial activity due to a bacteriocin produced during early growth and until the stationary phase of growth was reached (at optimum of 60% dissolved oxygen saturation). Its size was determined by electrospray ionization mass spectrometric analysis as 3.660 kDa. N-terminal sequencing showed that the bacteriocin had 19 amino acid residues in the order KYYGXNGVXTXGKHSXVDX. The purified bacteriocin is similar to pediocins isolated by various Pediococci and therefore, it belongs to the class IIa of bacteriocins and is thus designated pediocin SA-1. Sensitivity of the purified pediocin to various storage temperatures and enzyme treatments was examined. Purified pediocin SA-1 is heat stable for up to 60 min at 121 degrees C. Pediocin SA-1 is inhibitory to several food-borne pathogens and food spoilage bacteria. It appears to be significantly more effective against Listeria spp. compared to pediocin PD-1 produced by P. damnosus. The mode of action of the purified bacteriocin appears to be bactericidal.
Subject(s)
Bacteriocins/isolation & purification , Bacteriocins/pharmacology , Pediococcus/chemistry , Amino Acid Sequence , Bacteria/classification , Bacteria/drug effects , Bacteriocins/biosynthesis , Bacteriocins/chemistry , Bioreactors , Drug Stability , Glucose/metabolism , Kinetics , Lactates/metabolism , Microbial Sensitivity Tests , Molecular Sequence Data , Pediococcus/growth & development , Pediococcus/metabolism , Peptide Hydrolases/metabolism , ThermodynamicsSubject(s)
Escherichia coli O157/growth & development , Food Handling/methods , Food Microbiology , Milk/microbiology , Yogurt/microbiology , Animals , Cattle , Colony Count, Microbial , Disease Outbreaks , Fermentation , Food Contamination , Humans , Hydrogen-Ion Concentration , Sheep , Time FactorsABSTRACT
The viability of Campylobacter jejuni strains FRI-CF 401S and FRI-CF 25 inoculated in fresh and frozen beef hamburgers was investigated. Hamburgers were stored in the following conditions: 100% air at 4°C for 15 days, 100% CO2, and 100% N2 atmospheres at 4°C for 60 days and -18°C for 90 days. The data showed that 100% air was the most toxic atmosphere to C. jejuni strains. The C. jejuni populations decreased significantly faster (P ≤ 0.05) in the inoculated hamburgers in modified atmospheres than in those at -18°C. Fresh or frozen beef hamburgers contaminated by C. jejuni could always be a principal source of human campylobacteriosis.
