title: Development of a method to quantify in vitro the synergistic activity of "natural" antimicrobials.
abstract: Despite numerous papers being published on the use of hurdle technology to control food-borne pathogens or spoilage organisms, there is no commonly accepted methodology to quantify the level of synergistic activity. This paper describes a method to quantify in vitro the synergistic activity of antibacterial agents against bacteria. Initially, a microtiter plate growth assay was used to determine the inhibitory concentrations of four "natural" antimicrobials (nisin, lauricidin, totarol, and the lactoperoxidase system (LPS)) against a panel of eight bacteria. Using the same microtiter system, the impact of various combinations of antimicrobials was assessed. The degree of synergy was based on the analysis of three criteria: (1) increase in lag phase, (2) reduction in culture density after 24 h, (3) and residual viability at 24 h. Only the lactoperoxidase system was active against all the Gram-positive and Gram-negative bacteria tested. Nisin, lauricidin, and totarol were only effective against the Gram-positive bacteria. The method successfully identified three combinations (nisin-lauricidin, LPS-nisin, and LPS-lauricidin) previously reported to have synergistic activity and highlighted the synergistic activity of two novel combinations (nisin-totarol and LPS-totarol). The development of a quick and reliable method to identify and quantify synergistic activity is a useful screening tool to establish preservative techniques that could have potential antimicrobial synergy in food-based systems.
authors.affiliation: Microbiology Department, University of Otago, PO Box 56, 9001 Dunedin, New Zealand. dufmu681@student.otago.ac.nz
authors.forename: M
authors.initials: M
authors.lastname: Dufour
authors.forename: R S
authors.initials: RS
authors.lastname: Simmonds
authors.forename: P J
authors.initials: PJ
authors.lastname: Bremer
mesh_terms: D045784:Abietanes; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001419:Bacteria / Q000187:drug effects* / Q000254:growth & development*; D015169:Colony Count, Microbial; D004224:Diterpenes; D004357:Drug Synergism; D005516:Food Microbiology; D005989:Glycerides; D006090:Gram-Negative Bacteria / Q000187:drug effects / Q000254:growth & development; D006094:Gram-Positive Bacteria / Q000187:drug effects / Q000254:growth & development; D007784:Lactoperoxidase / Q000378:metabolism; D007848:Laurates; D008826:Microbial Sensitivity Tests; D050178:Monoglycerides; D009561:Nisin
chemical_list: D045784:Abietanes; D000900:Anti-Bacterial Agents; D004224:Diterpenes; D005989:Glycerides; D007848:Laurates; D050178:Monoglycerides; D009561:Nisin; C020777:monolaurin; C078548:totarol; D007784:Lactoperoxidase