Philippe Thonart

Efficiency of a Lactobacillus plantarum-xylanase combination on growth performances, microflora populations, and nutrient digestibilities of broilers infected with Salmonella Typhimurium

Three experiments were performed to assess the ability of a Lactobacillus plantarum probiotic combined with a xylanase to reduce the effects of Salmonella Typhimurium infection in broiler chickens from 1 to 30 or 42 d of age. Chicks were challenged at 3 d of age with 10(8) or 10(5) cfu Salmonella Typhimurium/chick. Four diets were studied: a wheat-based diet (C+) supplemented with 0.1 g/kg of xylanase (E) or 10(6) cfu/g of L. plantarum (P), or both (PE). Uninfected chicks fed the C diet were used as negative control (C-). Six or 8 chicks were housed per cage with 9 cages/treatment. Growth performance and feed conversion ratio (FCR) were recorded weekly. In experiment 1, bacterial enumeration in ceca was achieved using the fluorescent in situ hybridization technique. Salmonella enumeration was realized in excreta by microbiological cultures (experiments 2 and 3). Nutrient digestibilities and AME(n) were determined in experiment 3 from d 35 to 39. Infection with Salmonella Typhimurium led to a significant decrease in the daily weight gain (DWG) by 23.6 to 32.8%, whereas FCR was increased by 1.0 to 19.7%. Chickens fed the PE diet showed significantly improved performance in comparison with C+ birds (DWG: +12.5% in experiment 1; FCR: -2.1 to 8.6%), and in comparison with the P and E treatments (DWG: +6.3 to 8.3% in experiment 1; FCR: -2.7 to 6.4%). In experiment 3, the FCR was significantly improved by 3% with the PE diet in comparison with C- chickens. The PE combination tended to restore a microflora similar to that of uninfected broilers, whereas the P and E diets had less of an effect on the profile of bacterial communities. At slaughter age, Salmonella contamination was reduced by 2.00 and 1.85 log colony-forming units for the E and PE treatment, respectively. The PE diet significantly reduced the crude fat digestibility by 9.2%, in comparison with the C+ chickens. These results suggest that the combination between L. plantarum and a xylanase as feed additive could be effective for reduction of the detrimental effect after Salmonella Typhimurium infection of broilers.

Ecological fitness of Bacillus subtilis BGS3 regarding production of the surfactin lipopeptide in the rhizosphere

Cyclic lipopeptides and particularly surfactins produced by Bacillus species retain antibacterial, antiviral, biofilm-forming and plant resistance-inducing activities. In most cases, their role in biological control of plant diseases was evoked on the basis of in vitro assays or by using non-producing/overproducing mutants but there is a need for more direct evidence of an efficient lipopeptide biosynthesis in the rhizosphere. In this work, we coupled LC-MS quantification of the lipopeptides secreted by cells colonizing tomato plants with the use of psrfA-lacZ reporter system integrated within the BGS3 chromosome to study the expression of the surfactin operon in planta. Results showed that a higher level of psrfA induction was observed upon the establishment of a stable BGS3 population on roots and surfactins extracted from the rhizosphere were produced in biologically significant quantities. Our results also demonstrate that BGS3 efficiently utilizes the main substrates from plant exudates to produce surfactins. This synthesis is also efficient in cells forming colonies and the production may be favoured in bacteria developing slowly in the rhizosphere. This provides a first understanding of how environmental factors may influence lipopeptide production by beneficial Bacillus strains.

The Roles of Cyclic Lipopeptides in the Biocontrol Activity of Bacillus subtilis

Bacillus subtilis species are well-known and extensively-used beneficial rhizobacteria for biocontrol of plant diseases. Their interest arises from their ability to generate a broad array of bioactive metabolites among which three families of cyclic lipopeptides (CLPs). These CLPs display a huge diversity of structures and physico-chemical and biological properties which probably account for an important part of the biocontrol potential of the producing strains. Beside their antimicrobial properties, they are also involved in colonization and motility as well as in the systemic stimulation of immune system of the host plant. We summarize here the current knowledge of CLPs activities and focus on the recent findings in the context of biocontrol.

Efficiency of Neutralized Antibacterial Culture Supernatant from Bacteriocinogenic Lactic Acid Bacteria Supplemented With Salt in Control of Microorganisms Present in Senegalese Artisanally Handled Fish by Immersion Preservative Technology During Guedj Seafood Processing at 10ðC and 30ðC.

Senegal is a Western African country known for the importance of its marine resources. Artisanal fisheries contribute 85% of the total annual catch reaching 403,911 tons. Preserving approach during traditionally marine resource processing into indigenous seafood products is based on salt overuse. Guedj, a popular fermented indigenous seafood product, is the typical 30°C over salted transformed marine resource commodity across the country. One of the procedures for guedj production is immersing fish in water with sodium chloride at a concentration of over 30% (w/v) for preliminaryfermentation during 24 hr to 48 hr to develop flavor followed by additional dry-salting and sun drying. nThis study presents the level of microorganisms in fillets from lean, moderately fat and fatty artisanally handled fish, the efficacy of immersion in over salted [NaCl 60% (w/v)] water and 30°C incubation to control spoilage bacteria present in the fish matrixes, compared to those of lower salted [NaCl 14% (w/v)] antibacterial neutralized cell free culture supernatants (NCFCS) from two bacteriocinogenic lactic acid bacteria (LAB) and 10°C refrigeration. The two bacteriocinogenic bacteria (Lactococcus lactis subsp. lactis CWBI-B1410 and Lactobacillus curvatus CWBI-B28) were characterized in previous studies. Microbial population reduction in the treated fish was monitored using a 6 log10 CFU/g level at the end of storage. nThe levels of the total viable microbial counts of raw flesh were similar for the three fish, and barely with the acceptable limit of 6 log10 CFU/g. The over salting preservation at 30°C did not enable reduction of microbial populations present in the fish. The total viable microbial, enteric and LAB counts of fillets immersed in the salted antimicrobial NCFCS from the bacteriocinogenic strains decreased and were maintained under the acceptable limit for 13 days to 18 days during incubation at 10°C. nThese results indicate that the new preservative approach can reduce the need of abusive salt for guedj like products.

Preservation of Vinegar Acetic Acid Bacteria

A starter culture is defined as a collection of microbial cells that are capable of initiating and completing a rapid fermentation process. The microorganisms used as starter cultures in industrial applications, such as lactic acid bacteria and yeasts, are usually conserved either in a frozen or a powdered form via the freeze-drying, spray-drying or fluidization processes (To and Etzel, 1997). With regard to acetic acid bacteria (AAB), three forms of starter culture are used in vinegar making: n n nLiquid inoculum used in the culture surface method or Orleans method, submerged method, or immobilization method (Ohmori et al.,1982). n n nDried starter,as recently used by Sokollek et al.(1998)and Ndoye et al.(2007a) for submerged fermentation into Frings and Chansard acetators,respectively. n n nVinegar made from wine,using mixed strains from raw materials (Gullo et al., 2006).