A total of 221 strains of Lactobacillus isolated from meat and meat products were screened for antagonistic activities under conditions that eliminated the effects of organic acids and hydrogen peroxide. Nineteen strains of Lactobacillus sake, three strains of Lactobacillus plantarum, and one strain of Lactobacillus curvatus were shown to inhibit the growth of some other lactobacilli in an agar spot test; and cell-free supernatants from 6 of the 19 strains of L. sake exhibited inhibitory activity against indicator organisms. Comparison of the antimicrobial spectra of the supernatants suggested that the inhibitory compounds were not identical. One of the six strains, L. sake Lb 706, was chosen for further study. The compound excreted by L. sake Lb 706 was active against various lactic acid bacteria and Listeria monocytogenes. Its proteinaceous nature, narrow inhibitory spectrum, and bactericidal mode of action indicated that this substance is a bacteriocin, which we designated sakacin A. Curing experiments with two bacteriocin-producing strains of L. sake resulted in mutants that lacked both bacteriocin activity and immunity to the bacteriocin. Plasmid profile analysis of L. sake Lb 706 and two bacteriocin-negative variants of this strain indicated that a plasmid of about 18 megadaltons may be involved in the formation of bacteriocin and immunity to this antibacterial compound. In mixed culture, the bacteriocin-sensitive organisms were killed after the bacteriocin-producing strain reached maximal cell density, whereas there was no decrease in cell number in the presence of the bacteriocin-negative variant. Images

Antibacterial activity of Lactobacillus sake isolated from meat.

Lactic acid bacteria (LAB) constitute a group of gram-positive bacteria united by a constellation of morphological, metabolic, and physiological characteristics The general description of the bacteria included in the group is gram-positive, nonsporing, nonrespiring cocci or rods, which produce lactic acid as the major end product during the fermentation of carbohydrates The LAB term is intimately associated with bacteria involved in food and feed fermentation, including related bacteria normally associated with the (healthy) mucosal surfaces of humans and animals The boundaries of the group have been subject to some controversy, but historically the genera Lactobacillus, Leuconostoc, Pediococcus, and Streptococcus form the core of the group Taxonomic revisions of these genera and the description of new genera mean that LAB could, in their broad physiological definition, comprise around 20 genera However, from a practical, food-technology point of view, the following genera are considered the principal LAB: Aerococcus, Carnobacterium, Enterococcus, Lactobacillus, Lactococcus, Leuconostoc, Oenococcus, Pediococcus, Streptococcus, Tetragenococcus, Vagococcus, and Weissella The genus Bifidobacterium, often considered in the same context as the genuine lactic acid bacteria and sharing some of their typical features, is phylogenetically unrelated and has a unique mode of sugar fermentation The classification of lactic acid bacteria into different genera is largely based on morphology, mode of glucose fermentation, growth at different temperatures, configuration of the lactic acid produced, ability to grow at high salt concentrations, and acid or alkaline tolerance Chemotaxonomic markers such as fatty acid composition and constituents of the cell wall are also used in classification In addition, the present taxonomy relies partly on true phylogenetic relationships,

Lactic acid bacteria: classification and physiology.

In vitro selection criteria for probiotic bacteria of human origin: correlation with in vivo findings

Minimally processed fresh (MPF) fruits and vegetables are good media for growth of microorganisms. They have been involved in outbreaks because of the consumption of products contaminated by pathogens. They are also sensitive to various spoilage microorganisms such as pectinolytic bacteria, saprophytic Gram-negative bacteria, lactic acid bacteria, and yeasts. Contamination of MPF fruits and vegetables occurs at every stage of the food chain, from cultivation to processing. Polluted environments during cultivation or poor hygienic conditions in processing increase the risk of contamination with foodborne pathogens. Although MPF fruits and vegetables may harbor psychrotrophic microorganisms such as fluorescent pseudomonads or Listeria monocytogenes, good control of refrigeration temperature limits growth of spoilage and pathogenic microorganisms. Modified atmospheres are often efficient to maintain or improve visual organoleptic quality of MPF fruits and vegetables, but their effects on microorganisms are inconsistent. Chemical disinfection can partially reduce the initial bacterial contamination; irradiation seems to be more efficient. The applications of legislations and quality assurance systems to control contamination, survival, and growth of foodborne pathogens in MPF fruits and vegetables are discussed.

The microbiology of minimally processed fresh fruits and vegetables

Yogurt as probiotic carrier food

SUMMARY: An improved growth medium for lactobacilli is described. It supports good growth of lactobacilli generally and also is particularly useful for a number of fastidious strains which grow only poorly in other general media. In addition, tomato juice, a highly variable material, is not required. In a slightly modified form, it can also be used as a basal medium for fermentation tests.

J. C. De Man

Papers

A medium for the cultivation of lactobacilli