Antiviral effect of cationic compounds on bacteriophages.

The antiviral activity of several cationic compounds - cetyltrimethylammonium bromide (CTAB), chitosan, nisin, and lysozyme - was investigated on the bacteriophage c2 (DNA head and non-contractile tail) infecting Lactococcus strains and the bacteriophage MS2 (F-specific RNA) infecting E. coli. Firstly, these activities were evaluated in a phosphate buffer pH 7 - 10 mM. The CTAB had a virucidal effect on the Lactococcus bacteriophages, but not on the MS2. After 1 min of contact with 0.125 mM CTAB, the c2 population was reduced from 6 to 1.5 log(pfu)/mL and completely deactivated at 1 mM. On the contrary, chitosan inhibited the MS2 more than it did the bacteriophages c2. No antiviral effect was observed for the nisin or the lysozyme on bacteriophages after 1 min of treatment. A 1 and 2.5 log reduction was respectively observed for nisin and lysozyme when the treatment time increased (5 or 10 min). These results showed that the antiviral effect depended both on the virus and structure of the antimicrobial compounds. The antiviral activity of these compounds was also evaluated in different physico-chemical conditions and in complex matrices. The antiviral activity of CTAB was impaired in acid pH and with an increase of the ionic strength. These results might be explained by the electrostatic interactions between cationic compounds and negatively charged particles such as bacteriophages or other compounds in a matrix. Milk proved to be protective suggesting the components of food could interfere with antimicrobial compounds.

Description of a French natural wheat sourdough over 10 consecutive days focussing on the lactobacilli present in the microbiota.

Sourdoughs are complex ecosystems which are widely used to produce baked goods. This study aimed to provide a dynamic description of an industrial French sourdough ecosystem over 10 consecutive days. The sourdough was obtained from a natural fermentation that has been propagated over several years by the traditional backslopping method. The physico-chemical properties (pH, temperature, total titratable acidity) and the diversity of the lactobacilli among the microbiota were analyzed. A culture-dependent approach provided genotypic (REP-PCR) and phenotypic characterizations. The ecosystem showed a cyclic dynamic. The pH ranged from 3.41 to 3.7 and the acidity levels from 13.9 to 22.4 ml NaOH. A stable lactobacilli microbiota was observed in the sourdough over the 10 days. It was composed of four predominant species assigned to Lactobacillus panis, Lactobacillus frumenti, Lactobacillus amylolyticus and Lactobacillus acetotolerans. The phenotypic tests highlighted an acidification function for the Lb. amylolyticus and Lb. acetotolerans populations, whereas the Lb. panis and Lb. frumenti populations seemed more aromatic. Therefore, this natural sourdough was composed of an atypical microbial association.

Direct Quantitative Detection and Identification of Lactococcal Bacteriophages from Milk and Whey by Real-Time PCR: Application for the Detection of Lactococcal Bacteriophages in Goat's Raw Milk Whey in France.

The presence of Lactococcus bacteriophages in milk can partly or completely inhibit milk fermentation. To prevent the problems associated with the bacteriophages, the real-time PCR was developed in this study for direct detection from whey and milk of three main groups of Lactococcus bacteriophages, c2, 936, and P335. The optimization of DNA extraction protocol from complex matrices such as whey and milk was optimized allowed the amplification of PCR without any matrix and nontarget contaminant interference. The real-time PCR program was specific and with the detection limit of 10(2) PFU/mL. The curve slopes were -3.49, -3.69, and -3.45 with the amplification efficiency estimated at 94%, 94%, and 98% and the correlation coefficient (R(2)) of 0.999, 0.999, and 0.998 for c2, 936 and P335 group, respectively. This method was then used to detect the bacteriophages in whey and goat's raw milk coming from three farms located in the Rhône-Alpes region (France).

Comparative study of culture media used for sourdough lactobacilli.

Eleven culture media were analysed to compare their exhaustiveness for the quantification of lactobacilli type I sourdoughs. The media tested were MRS, maltose modified MRS, MRS5, SDB, SFM, MRS "Vogel", Rogosa as elective media, and FH, OH, LAMVAB, KCA as selective media. Six broth media were also tested for colony subculture. Quantitatively, maltose MRS and MRS media showed the highest counts - respectively 9.47 and 9.43 mean log(cfu)/g. SFM and Rogosa media presented slighlty lower levels - 9.1 and 9.24 log(cfu)/g respectively. Levels on the remaining media were significantly lower - lesser than 0.5 log(cfu)/g compared to maltose MRS and MRS media. From a qualitative standpoint, the bacterial diversity, based on the comparison of the whole-cell protein patterns of isolates, was the largest on maltose MRS medium. However, MRS5 medium allowed the isolation of a specific population only found on this medium. For colony subculture, maltose MRS and MRS5 appeared the most appropriate broth media. These results underline that there is no really efficient medium for the systemic study of sourdoughs. Therefore, the first step before working on these ecosystems implies a deliberate choice of the most appropriate media combination.