A study was conducted to investigate the effect of mannan oligosaccharide (MOS) on the gut microbiota and intestinal morphology of rainbow trout under commercial farming conditions. Juvenile (mean initial BW 38.2 +/- 1.7 g) and subadult (111.7 +/- 11.6 g) trout were fed 2 dietary treatments for 111 and 58 d, respectively. The control treatment consisted of a standard commercial diet, and the MOS treatment consisted of the control diet supplemented with 0.2% MOS. Morphology of the anterior and the posterior intestine was examined with light and electron microscopy. Light microscopy demonstrated increased gut absorptive surface area in the subadult MOS group. Additionally, electron microscopy revealed an increase in microvilli length and density in the subadult MOS group compared with the control (P < 0.05). However, no significant improvements were detected in the juvenile group. Culture-based evaluation of the intestinal microbiota showed that MOS significantly reduced (P < 0.05) the viable intestinal bacterial populations (by approximately 2 log scales in all cases). Levels of Aeromonas/Vibrio spp. were significantly decreased (P < 0.05) in the juvenile MOS group (9% of the total microbiota) compared with the juvenile control group (37%). Additionally, analysis of microbial communities was conducted using denaturing gradient gel electrophoresis of PCR-amplified 16S rDNA. The denaturing gradient gel electrophoresis fingerprinting revealed an alteration of bacterial populations; analysis of similarity, similarity percentages, and nonmetric multidimensional scaling analysis showed that MOS reduced species richness and increased similarity of bacterial populations found within the subadult and juvenile groups. The current study shows that MOS modulates intestinal microbial communities, which subsequently improve gut morphology and epithelial brush border.

Rainbow trout were fed either a diet containing fishmeal (FM) as the crude protein source or a diet containing 50% replacement with soybean meal (SBM) for 16 weeks. An enteritis-like effect was observed in the SBM group; villi, enterocytes and microvilli were noticeably damaged compared with the FM group. The posterior intestine microvilli of SBM-fed fish were significantly shorter and the anterior intestine microvilli significantly less dense than the FM-fed fish. Electron microscopy confirmed the presence of autochthonous bacterial populations associated with microvilli of both fish groups. Reduced density of microvilli consequently led to increased exposure of enterocyte tight junctions, which combined with necrotic enterocytes is likely to diminish the protective barrier of the intestinal epithelium. No significant differences in total viable counts of culturable microbial populations were found between the groups in any of the intestinal regions. A total of 1500 isolates were tentatively placed into groups or genera, according to standard methods. Subsequent partial 16S rRNA sequencing revealed species that have not been identified from the rainbow trout intestine previously. Compared with the FM group levels of Psychrobacter spp. and yeast were considerably higher in the SBM group; a reduction of Aeromonas spp. was also observed.

The effect of dietary probiotics (Bacillus subtilis, Bacillus licheniformis and Enterococcus faecium) used singularly and synergistically on the growth performance, intestinal microbiota and health status of rainbow trout (Oncorhynchus mykiss Walbaum) were assessed after 10 weeks feeding on supplemented diets. No significant improvements of weight gain or specific growth rate were observed in the probiotic fed groups. However, a significant improvement of feed conversion ratio was observed in the group fed E. faecium. High levels of probiotic species were observed in the posterior gastrointestinal tract as transient digesta‐associated populations and potentially resident mucosal populations. Bacillus subtilis and B. licheniformis levels accounted for 36% of the total culturable microbial population adhered to the mucosa and 62% in the digesta. E. faecium levels accounted for 45% of the mucosal population and 89% of the population in the digesta. An increase of serum lysozyme activity was observed in the fish fed diets containing the Bacillus probionts and elevated leukocyte levels were observed in fish fed diets containing Bacillus + E. faecium synergistically. The results of the current study demonstrate potential for B. subtilis, B. licheniformis and E. faecium to improve feed utilization, modulate intestinal microbiota and the health status of rainbow trout.

The effect of dietary probiotics (Bacillus subtilis, Bacillus licheniformis and Enterococcus faecium) was assessed on rainbow trout (Oncorhynchus mykiss Walbaum) previously treated with oxolinic acid. After feeding on supplemented diets for 10 weeks growth performance, feed utilization, gastrointestinal colonization and health status were assessed. B. subtilis + B. licheniformis fed fish displayed a significant improvement of feed conversation ration (FCR), specific growth rate (SGR) and protein efficiency ratio (PER). High levels of probiotic species were observed in the posterior gastrointestinal tract as transient digesta associated populations and potentially resident mucosal populations. Levels of Bacillus spp. reached log 3.74 CFU g−1 on the mucosal epithelium and log 7.41 CFU g−1 in the digesta of fish fed diets supplemented with B. subtilis and B. licheniformis. Enterococci levels reached log 2.84 CFU g−1 on the mucosa and log 7.78 CFU g−1 in the digesta of fish fed E. faecium supplemented diets. Feeding trout the Bacillus probionts alone or synergistically with E. faecium resulted in elevated leucocyte levels. The results of the current study demonstrate a potential role of probiotics for stabilizing/reinforcing the gastrointestinal microbiota after antibiotic treatment. This could reinvigorate the intestinal defensive barrier mechanism and provide protection against secondary potential pathogens.

Bacterial communities from the intestinal tract of rainbow trout were investigated to assess transient and resident microbial communities using both culture‐based and culture‐independent techniques. Viable counts attached to the intestinal mucosa were in the range of log 4.77–5.38 and log 6.67–6.79 CFU g−1 in the intestinal contents. Pseudomonas spp. and Enterobacteriaceae constituted nearly 80% of the allochthonous population but <60% of the autochthonous populations. This coincided with an elevated mucosal level of a group of Gram‐positive rods from ∼2% in the digesta to 25–35% on the mucosa. This group was identified by 16S rRNA as Arthrobacter aurescens and Janibacter spp. HTCC2649. Analysis of denaturing gradient gel electrophoresis banding patterns showed complex communities in all intestinal regions. Similarity coefficients showed that mucosal communities were ∼70% similar to digesta communities and yet due to the presence of bands found uniquely either in the digesta or on the mucosa, the communities are distinctly different. Scanning electron microscopy confirmed mucosal bacterial populations and highlighted a possible localized colonization between mucosal folds. The study highlights the complexity of resident microbial communities that have not been fully explored in previous rainbow trout studies; this is especially true with probiotic/prebiotic investigations.

A study was conducted to assess the probiotic effect of different dietary forms of Pediococcus acidilactici on rainbow trout (Oncorhynchus mykiss Walbaum). Growth performance, feed utilization, intestinal colonization and basic health status were investigated after a 10 week feeding trial. Fish were fed either vegetative (Veg) or lyophilized (Lyo) cells incorporated into a basal diet at either 107 (Lo) or 108 (Hi) CFU g−1. P. acidilactici temporarily colonized the digestive tract (as both epithelium associated and transient populations) in all probiotic groups during supplemented feeding. Scanning electron microscopy confirmed the presence of localized colonization of P. acidilactici‐like cells between intestinal folds of the probiotic fed fish. Compared to the control group, no significant improvements in growth performance, feed utilization or carcass composition were observed in the probiotic fed fish (P > 0.05). However, a significant reduction of condition factor (K) was evident in fish fed the lyophilized diets. Increased leucocyte levels were observed in fish fed the low level vegetative P. acidilactici supplemented diet yet leucocyte types were not affected. The study demonstrates some potential for the application of P. acidilactici with rainbow trout but further research is required to optimize applications.

Bovine tuberculosis (BTB) is widespread but poorly controlled in Africa and M. bovis is posing threats to human health. The risk of cattle handlers to M. bovis prevalence and public health significance of BTB in Cameroon were assessed. Slaughter inspection records from major cities revealed that BTB detection rates in cattle from 0.18% to 4.25% and BTB lesions were most common. Analyses of tissues and sera confirmed BTB in 31% (Ziehl-Neelsen), 51% (culture), and 60% (antibody detection) of test cattle. Among cattle handlers, 81.9% were aware of BTB, 67.9% knew that BTB is zoonotic, and 53.8% knew one mode of transmission but over 27% consumed raw meat and/or drank unpasteurized milk. Respondents who had encountered tuberculosis cases were more informed about zoonotic BTB (P < .05). Tuberculosis is prevalent in cattle destined for human consumption in Cameroon with serious public health implications. Targeted monitoring of infected animal populations and concerted veterinary/medical efforts are essential for control.

We compared induction of the viable-but-nonculturable (VBNC) state in two Vibrio spp. isolated from diseased corals by starving the cells and maintaining them in artificial seawater at 4 and 20°C. In Vibrio tasmaniensis, isolated from a gorgonian octocoral growing in cool temperate water (7 to 17°C), the VBNC state was not induced by incubation at 4°C after 157 days. By contrast, Vibrio shiloi, isolated from a coral in warmer water (16 to 30°C), was induced into the VBNC state by incubation at 4°C after 126 days. This result is consistent with reports of low-temperature induction in several Vibrio spp. A large proportion of the V. tasmaniensis population became VBNC after incubation for 157 days at 20°C, and V. shiloi became VBNC after incubation for 126 days at 20°C. Resuscitation of V. shiloi cells from cultures at both temperatures was achieved by nutrient addition, suggesting that starvation plays a major role in inducing the VBNC state. Our results suggest that viable V. shiloi could successfully persist in the VBNC state in seawater for significant periods at the lower temperatures that may be experienced in winter conditions, which may have an effect on the seasonal incidence of coral bleaching. For both species, electron microscopy revealed that prolonged starvation resulted in transformation of the cells from rods to cocci, together with profuse blebbing, production of a polymer-like substance, and increased membrane roughness. V. shiloi cells developed an increased periplasmic space and membrane curling; these features were absent in V. tasmaniensis.The viable-but-nonculturable (VBNC) state in bacteria has been defined as "a cell that can be demonstrated to be metabolically active, while being incapable of undergoing a sustained cellular division required for growth in or on a medium normally supporting growth of that cell" (20). So far, the VBNC state has been reported for about 60 different species (22) and has been demonstrated both in the laboratory and in situ (23). The conditions inducing the VBNC state are as diverse as the species themselves; however, all inducing factors generally are some form of environmental stress, such as starvation or changes in temperature or salinity, suggesting that the VBNC state may be an adaptive or dormant state allowing survival under adverse conditions (4,(20)(21)(22)29).The VBNC state was first described for Vibrio cholerae (36) and has since been characterized for at least 11 Vibrio species. The VBNC state in vibrios is generally induced by incubation at low temperatures (4 to 6°C), while elevated temperatures (Ͼ25°C) induce the same state in non-Vibrio species (10). As a part of our study of the effects of environmental temperatures on the symbiotic and pathogenic associations of bacteria with corals, we compared the effects of prolonged incubation at different temperatures on the survival of two Vibrio spp. that have been associated with coral disease in very different habitats.Vibrio shiloi has been confirmed to cause bleaching in the coral Oculina patagoni...