Development and use of a selective medium for isolation of Leuconostoc spp. from vegetables and dairy products.

Institut Agronomique et Veterinaire Hassan II, Departement de Microbiologie Alimentaire et de Biotechnologie, Rabat-Instituts, Morocco.
Applied and Environmental Microbiology (Impact Factor: 3.95). 03/1993; 59(2):607-9.
Source: PubMed

ABSTRACT A selective medium (LUSM medium) for the isolation of Leuconostoc spp. was developed. This medium contained 1.0% glucose, 1.0% Bacto Peptone (Difco), 0.5% yeast extract (BBL), 0.5% meat extract (Difco), 0.25% gelatin (Difco), 0.5% calcium lactate, 0.05% sorbic acid, 75 ppm of sodium azide (Sigma), 0.25% sodium acetate, 0.1% (vol/vol) Tween 80, 15% tomato juice, 30 micrograms of vancomycin (Sigma) per ml, 0.20 microgram of tetracycline (Serva) per ml, 0.5 mg of cysteine hydrochloride per ml, and 1.5% agar (Difco). LUSM medium was used successfully for isolation and enumeration of Leuconostoc spp. in dairy products and vegetables. Of 116 colony isolates obtained from fresh raw milk, curdled milk, or various vegetables, 115 were identified as members of the genus Leuconostoc. A total of 89 of these isolates were identified to species; 13.5% of the isolates were Leuconostoc cremoris, 7.9% were Leuconostoc mesenteroides subsp. mesenteroides, 11.2% were Leuconostoc mesenteroides subsp. dextranicum, 16.9% were Leuconostoc mesenteroides subsp. paramesenteroides, 10.1% were leuconostoc lactis, and 40.4% were Leuconostoc oenos. When we compared the counts obtained for two Leuconostoc strains, Leuconostoc dextranicum 181 and L. cremoris JLL8, on MRS agar and LUSM medium, we found no significant difference between the values obtained on the two media.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Root rot in sugar beet (Beta vulgaris) causes significant losses worldwide. To assess the distribution of root rot fungi and their relationship to bacterial root rot, commercial sugar beet roots with rot symptoms were collected at harvest time in the Intermountain West. Isolations for both fungi and bacteria were conducted using standard microbiological techniques, and the root area rotted was assessed. A subset of fungal isolates was tested for pathogenicity to sugar beet in greenhouse assays and field trials with and without manure. In the field survey of rotting beets, the fungi most frequently associated with root rot included Fusarium spp. (Fusarium oxysporum and Fusarium acuminatum with 24% and 15% of isolates, respectively), Geotrichum spp. (16% of isolates), Rhizoctonia solani (15% of isolates), and Mucor spp. (14% of isolates). However, only R. solani isolate F321 (AG-2-2IIIB) consistently caused rot in greenhouse pathogenicity tests. In the field survey, a mean of 6% of the root tissue had rotted for individual roots when fungi were isolated individually, whereas mean root rot was 71% and 68% when bacteria were isolated individually or in combination with other organisms, respectively. In field trials, roots inoculated with F321 averaged 3%–5% fungal rot, whereas the percentage of root tissue with bacterial rot was 6%–78%, which supports survey observations. Manure did not lead to root rots in the field. Traditionally, fungal root rots have been the main focus of breeding programs; however, because of the root area rotted by lactic acid bacteria, especially Leuconostoc, these bacteria should not be ignored in breeding efforts.
    Canadian Journal of Plant Pathology 06/2009; 31(2):232-240. · 0.99 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Kefir grains are used in dairy plants for mother or bulk starter culture production. The aim of the study was to evaluate the possibility of the re-use of kefir grains grown at 18 °C for 24 h in pasteurized Escherichia coli contaminated milk up to 6.1 × 102 cfu.mL−1. The contamination rate was adapted to a realistic situation which may take place in plant. E. coli was enumerated in kefir grains, postharvest broth, and in milk incubated without kefir grains. Determination of the replication ability of the affected grains and acidification activity of postharvest broth was performed. The impact of milk contamination on total lactic acid bacteria (LAB), citrate-fermenting and vancomycin-tolerant LAB, and yeasts of the kefir grains and postharvest broth was evaluated. The grains separated from fermented milk and washed with water were not E. coli-contaminated. In the postharvest broth (starter culture), E. coli was found at inoculation rate, whereas in contaminated milks incubated without grains, E. coli population increased at least by 2 log. Separated from contaminated and uncontaminated milk, grains displayed similar growth dynamics in five subsequent transfers into freshly prepared milk. The postharvest broth obtained from last transfer was not contaminated and showed standard acidification milk profile. E. coli contamination of milk did not influence adversely the ratio of citrate-fermenting, vancomycin-tolerant LAB, yeasts, and total LAB counts in kefir grains and postharvest broth. These findings would have economical value for kefir producers, but it should be considered that only one strain with low contamination rate was tested.
    Dairy Science and Technology 11/2012; 92(6). · 1.13 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A one-step PCR-based method was constructed for the rapid detection of 10 common lactic acid bacteria (LAB) and Bifidobacterium. Ten primer pairs were designed based on the sequences that specify the 16S rRNA genes of Lactococcus lactis subsp. lactis, Lactococcus lactis subsp. cremoris, Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus fermentum, Lactobacillus helveticus, Bifidobacterium and Leuconostoc. The primers showed high specificity for target species. The detection limit was 104–105 cfu mL−1 for Lb. delbrueckii and 103–104 cfu mL−1 for the others. This method was applied to identify the species mentioned above, in situ, from 8 samples of traditional fermented milk, and monitor the constitution of the species in commercial dairy yoghurt. The results were consistent with the results of 16S rRNA sequencing, suggesting that the method was reliable for the rapid identification of LAB and Bifidobacterium used in fermented milk.
    International Dairy Journal 10/2014; · 2.30 Impact Factor

Full-text (2 Sources)

Available from
May 16, 2014