title: Inhibitory effects of nisin and potassium sorbate alone or in combination on vegetative cells growth and spore germination of Bacillus sporothermodurans in milk.
abstract: The inhibitory activities of nisin or/and potassium sorbate on spores and vegetative cells of Bacillus sporothermodurans LTIS27, which are known to be a contaminant of dairy products and to be extremely heat-resistant, were investigated. First, the tested concentrations of nisin or potassium sorbate inhibited vegetative cell growth; with the minimum inhibitory concentrations were 5 × 10(3) IU/ml and 2% (w/v), respectively. Then, the behaviour of vegetative cells and spores in presence of sub-lethal concentrations of nisin (50 UI/ml) or/and potassium sorbate (0.2%), in milk at 37 °C for 5 days, were evaluated. In the absence of inhibitors, strain grew and sporulated at the end of the exponential phase. Nisin (50 UI/ml) was able to inhibit spore outgrowth but didn't affect their germination. It induced an immediate and transitory reduction (1.6log(10) after 1 h and 2.8log(10) after 6 h of incubation) of vegetative cell growth which reappeared between 10 h and 24 h. Potassium sorbate (0.2%) had a durable bacteriostatic effect (1.1log(10) after 6 h), on vegetative cells, followed by a slower regrowth. It was able to inhibit both germination and outgrowth of spores. Association of nisin and potassium sorbate, at sub-lethal concentrations, showed a synergistic effect and resulted in a total inhibition of cells growth after 5 days. The results illustrate the efficacy of nisin and potassium sorbate in combination, and the commercial potential of applying such treatment to decontaminate any product that has a problem with persistence of bacterial spores.
authors.affiliation: Laboratory of Epidemiology and Veterinary Microbiology, Bacteriology and Biotechnology Development Groups, Institute Pasteur of Tunisia (IPT), University Manar, BP 74, 13 place Pasteur, Tunis-Belvédère 1002, Tunisia; Laboratory of Animal Resources and Food Technology, National Institute of Agronomy of Tunisia (INAT), University of Carthage 43, Rue Charles Nicole, Cité Mahrajène, Belvédère, 1082 Tunis, Tunisia. Electronic address: chediaaouadhi@yahoo.fr.
authors.forename: Chedia
authors.initials: C
authors.lastname: Aouadhi
authors.affiliation: Laboratory of Animal Resources and Food Technology, National Institute of Agronomy of Tunisia (INAT), University of Carthage 43, Rue Charles Nicole, Cité Mahrajène, Belvédère, 1082 Tunis, Tunisia.
authors.forename: Slah
authors.initials: S
authors.lastname: Mejri
authors.affiliation: Laboratory of Epidemiology and Veterinary Microbiology, Bacteriology and Biotechnology Development Groups, Institute Pasteur of Tunisia (IPT), University Manar, BP 74, 13 place Pasteur, Tunis-Belvédère 1002, Tunisia.
authors.forename: Abderrazak
authors.initials: A
authors.lastname: Maaroufi
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001407:Bacillus / Q000187:drug effects* / Q000254:growth & development; D005506:Food Contamination / Q000032:analysis / Q000517:prevention & control; D005519:Food Preservation / Q000379:methods*; D008892:Milk / Q000382:microbiology*; D009561:Nisin / Q000494:pharmacology*; D013011:Sorbic Acid / Q000494:pharmacology*; D013171:Spores, Bacterial / Q000187:drug effects / Q000254:growth & development*
chemical_list: D000900:Anti-Bacterial Agents; D009561:Nisin; D013011:Sorbic Acid
keywords: Antimicrobial agents; Bacillus sporothermodurans; Minimum inhibitory concentrations; Reduction; Synergistic effect