Probiotic bacteria as biological control agents in aquaculture

Biodiversity of vibrios

Vibrios are ubiquitous and abundant in the aquatic environment. A high abundance of vibrios is also detected in tissues and/or organs of various marine algae and animals, e.g., abalones, bivalves, corals, fish, shrimp, sponges, squid, and zooplankton. Vibrios harbour a wealth of diverse genomes as revealed by different genomic techniques including amplified fragment length polymorphism, multilocus sequence typing, repetetive extragenic palindrome PCR, ribotyping, and whole-genome sequencing. The 74 species of this group are distributed among four different families, i.e., Enterovibrionaceae, Photobacteriaceae, Salinivibrionaceae, and Vibrionaceae. Two new genera, i.e., Enterovibrio norvegicus and Grimontia hollisae, and 20 novel species, i.e., Enterovibrio coralii, Photobacterium eurosenbergii, V. brasiliensis, V. chagasii, V. coralliillyticus, V. crassostreae, V. fortis, V. gallicus, V. hepatarius, V. hispanicus, V. kanaloaei, V. neonatus, V. neptunius, V. pomeroyi, V. pacinii, V. rotiferianus, V. superstes, V. tasmaniensis, V. ezurae, and V. xuii, have been described in the last few years. Comparative genome analyses have already revealed a variety of genomic events, including mutations, chromosomal rearrangements, loss of genes by decay or deletion, and gene acquisitions through duplication or horizontal transfer (e.g., in the acquisition of bacteriophages, pathogenicity islands, and super-integrons), that are probably important driving forces in the evolution and speciation of vibrios. Whole-genome sequencing and comparative genomics through the application of, e.g., microarrays will facilitate the investigation of the gene repertoire at the species level. Based on such new genomic information, the taxonomy and the species concept for vibrios will be reviewed in the next years.

Characterization of Bacillus probiotics available for human use

Bacillus species (Bacillus cereus, Bacillus clausii, Bacillus pumilus) carried in five commercial probiotic products consisting of bacterial spores were characterized for potential attributes (colonization, immunostimulation, and antimicrobial activity) that could account for their claimed probiotic properties. Three B. cereus strains were shown to persist in the mouse gastrointestinal tract for up to 18 days postadministration, demonstrating that these organisms have some ability to colonize. Spores of one B. cereus strain were extremely sensitive to simulated gastric conditions and simulated intestinal fluids. Spores of all strains were immunogenic when they were given orally to mice, but the B. pumilus strain was found to generate particularly high anti-spore immunoglobulin G titers. Spores of B. pumilus and of a laboratory strain of B. subtilis were found to induce the proinflammatory cytokine interleukin-6 in a cultured macrophage cell line, and in vivo, spores of B. pumilus and B. subtilis induced the proinflammatory cytokine tumor necrosis factor alpha and the Th1 cytokine gamma interferon. The B. pumilus strain and one B. cereus strain (B. cereus var. vietnami) were found to produce a bacteriocin-like activity against other Bacillus species. The results that provided evidence of colonization, immunostimulation, and antimicrobial activity support the hypothesis that the organisms have a potential probiotic effect. However, the three B. cereus strains were also found to produce the Hbl and Nhe enterotoxins, which makes them unsafe for human use.

Immune enhancement in rainbow trout (Oncorhynchus mykiss) by potential probiotic bacteria (Lactobacillus rhamnosus)

The present study assessed the immune enhancement of fish by a lactic acid bacterium (LAB) Lactobacillus rhamnosus (ATCC 53103). The bacterium was administered orally at five different doses 7.9 x 10(4) (LAB4), 2.1 x 10(6) (LAB6), 2.8 x 10(8) (LAB8), 1.9 x 10(10) (LAB10) and 9.7 x 10(10) (LAB11) CFU/g feed to rainbow trout for two weeks and the feed was changed to un-supplemented diet. From the onset of feeding supplemented diets at 1, 2, 3 and 4 weeks, blood and mucus samples were taken. During the LAB feeding period L. rhamnosus persisted in the fish intestine and in the tank water in high numbers. However, L. rhamnosus disappeared from the intestine, skin mucus and tank water within one week after the change to the non-supplemented feed. In comparison to untreated control fish, respiratory burst activity of blood cells was raised significantly in the LAB4 treated group on week 2. Serum-mediated killing of Escherichia coli was increased significantly in group LAB6 on week 2. Serum immunoglobulin levels were significantly raised only in LAB8 group on week 1 and in LAB4 and LAB8 at the end of the trial. The results show that rainbow trout immune parameters were enhanced by using probiotic bacteria.

Vibrio fortis sp. nov. and Vibrio hepatarius sp. nov., isolated from aquatic animals and the marine environment

In this study, the taxonomic positions of 19 Vibrio isolates disclosed in a previous study were evaluated. Phylogenetic analysis based on 16S rDNA sequences partitioned these isolates into groups that were closely related (98.8-99.1 % similarity) to Vibrio pelagius and Vibrio xuii, respectively. DNA-DNA hybridization experiments further showed that these groups had <70 % similarity to other Vibrio species. Two novel Vibrio species are proposed to accommodate these groups: Vibrio fortis sp. nov. (type strain, LMG 21557(T)=CAIM 629(T)) and Vibrio hepatarius sp. nov. (type strain, LMG 20362(T)=CAIM 693(T)). The DNA G+C content of both novel species is 45.6 mol%. Useful phenotypic features for discriminating V. fortis and V. hepatarius from other Vibrio species include production of indole and acetoin, utilization of cellobiose, fermentation of amygdalin, melibiose and mannitol, beta-galactosidase and tryptophan deaminase activities and fatty acid composition.

Immunomodulatory effects of nisin in turbot (Scophthalmus maximus L.)

In the present work, the effect of nisin on the non-specific immune response of turbot (Scophthalmus maximus L.) leukocytes has been studied both in vitro and in vivo. The head kidney macrophage chemiluminescent (CL) response was significantly increased with intermediate doses of nisin (2.5 and 0.025 micro g ml(-1)) whilst the higher dose (25 micro g ml(-1)) significantly decreased the response after 24h incubation. When the incubation time was extended to 72 h, significant differences between doses were observed and the lower nisin concentration (0.025 micro g ml(-1)) appeared to be the optimum dose for increasing the CL response. The phagocytic activity of HK macrophages was also affected by in vitro nisin treatments. Nisin at 0.25 micro g ml(-1) and 0.025 micro g ml(-1) significantly stimulated the response after 24 and 72 h incubation respectively. Nitric oxide (NO) production by HK macrophages was not influenced by any nisin concentration employed for 24 or 72 h incubationsIn vivo, one week post injection, a slightly but non-significant stimulation of the CL response was observed with the lowest nisin concentration (0.0025 micro g fish(-1)). NO in serum and serum antibacterial index were not significantly affected by nisin treatments. On the other hand, lysozyme concentration in serum was significantly augmented with the lowest nisin dose (0.0025 micro g fish(-1)). The antibacterial effect of nisin against the fish pathogenic bacteria Carnobacterium piscicola (CECT 4020) was also demonstrated in vitro.

Vibrio neptunius sp. nov., Vibrio brasiliensis sp. nov. and Vibrio xuii sp. nov., isolated from the marine aquaculture environment (bivalves, fish, rotifers and shrimps)

The fluorescent amplified fragment length polymorphism (FAFLP) groups A5 (21 isolates), A8 (6 isolates) and A23 (3 isolates) distinguished in an earlier paper (Thompson et al., Syst Appl Microbiol 24, 520-538, 2001) were examined in more depth. These three groups were phylogenetically related to Vibrio tubiashii, but DNA-DNA hybridization experiments proved that the three AFLP groups are in fact novel species. Chemotaxonomic and phenotypic analyses further revealed several differences among the 30 isolates and known Vibrio species. It is proposed to accommodate these isolates in three novel species, namely Vibrio neptunius (type strain LMG 20536T; EMBL accession no. AJ316171; G +C content of the type strain 46.0 mol%), Vibrio brasiliensis (type strain LMG 20546T; EMBL accession no. AJ316172; G + C content of the type strain 45.9 mol%) and Vibrio xuii (type strain LMG 21346T; EMBL accession no. AJ316181; G +C content of the type strain 46.6 mol%). These species can be differentiated on the basis of phenotypic features, including fatty acid composition (particularly 14:0 iso, 14:0 iso 3-OH, 16:0 iso, 16:0, 17:0 and 17:1 omega8c), enzyme activities and utilization and fermentation of various carbon sources.

Moving from recommendation to implementation and audit: part 2. Review of interventions and audit

There are multiple interventions available that may help to control the development and spread of resistance to antimicrobial agents in bacteria implicated in community-acquired respiratory tract infections. Unfortunately, very few studies have assessed the effectiveness of these interventions using objective end-points, such as reduction in resistance rates and improvement in clinical outcomes. Most interventions are centered on reducing inappropriate or unnecessary use of antibiotics; others focus on reducing disease burden and bacterial colonization. With regard to antibiotic use, efforts should be concentrated at both the prescriber and consumer levels. Interventions that target prescribers include: provision of educational materials; strategies and tools to improve diagnosis; implementation of practice guidelines; personalized interactive sessions with feedback on the practice profile; and use of delayed prescription and alternative prescribing strategies. Optimal results are usually obtained when these interventions are combined with consumer education. Regulatory interventions (e.g. licensing regulations and controlled access to drugs), restrictions in the use of agents for growth promotion in animals, and use of nonantimicrobial therapies (e.g. probiotics) may help further to reduce inappropriate antibiotic use and thereby decrease the selective pressure for development of resistance. Infection-control strategies, public health measures, vaccination programs, and new antibiotics all have a role in minimizing the spread of resistant organisms. Ideally, resistance-control programs should include predefined criteria for success and integral audit processes based on objective end-points (antibiotic use, resistance trends, and health outcomes). Standardization of data collection is imperative so that the relative merits of various interventions can be compared. Effective implementation and audit of interventions is often difficult in developing countries owing to poor health-care infrastructures, lack of resources, poor education/training, and minimal regulatory controls on the supply and quality of antimicrobials. Substantial support from governments and health-care organizations across the globe is required to initiate and sustain effective intervention programs to control antimicrobial resistance.

Environmental biotechnology: the ongoing quest

Environmental biotechnology, until now, has primarily focused on the development of technologies to treat aqueous, solid and gaseous wastes. At present, the basic knowledge on how biotechnology can handle these wastes has been acquired and the focus is now on the implementation of these processes as 'best available technology not entailing excessive costs' (BATNEEC) in the framework of strict and transparent environmental legislation. New environmental challenges continue to evolve, as it becomes clear that waste streams should be tackled in an overall holistic way. New technologies to reach this goal are currently under development. Novel aspects with respect to the domain of water treatment are, for example, the biomembrane reactor technology and the newly discovered processes to remove nitrogen by means of anaerobic ammonium oxidation. Also, most challenging is the continuing strive for re-use of treated wastewater. Indeed, water shortage is emerging in an increasing number of countries all over the world and necessitates the short cycling of water. Finally, biotechnology has a key role to play in the novel approaches to design wastewater treatment based on decentralised sanitation and reuse (DESAR). Solid waste is a major challenge worldwide. The implementation of anaerobic digestion to treat biowastes has become a grown-up technology. New approaches in which biotechnological processes are linked to physical processes, such as plasma technology, certainly deserve special attention for the coming decades. Soil and sediment clean up by means of biostimulation/remediation/augmentation is now well established. Certainly, a number of prospects need to be further explored, such as the use of special energy sources to stimulate in situ the microbial community and the seeding of knowledge to the in situ community by means of horizontal gene transfer mechanisms. A number of waste gases can be handled by biofilter systems. Biological treatment of wastegases is also evolving, inasmuch as that besides conventional chemical pollutants, now also highly problematic chemicals (even dioxins) can be dealt with through proper biotechnological approaches. A remarkable new potential is the use of well designed probiotics to upgrade aquaculture and together with conventional biological water treatment processes, to guarantee the overall water quality of this domain of food production.

Bacteriophage therapy of infectious diseases in aquaculture

Bacteriophages may be candidates as therapeutic agents in bacterial infections. Here we describe the protective effects of phages against experimentally induced bacterial infections of cultured fish and discuss the potential for phage therapy in aquaculture.