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The effect of dietary β-glucan on the bacterial community in the gut of common carp (Cyprinus carpio) was examined after oral application of Aeromonas hydrophila. Carp received either feed supplemented with 1% MacroGard ® , a β-1,3/1,6-glucan, or a β-glucan-free diet. Fourteen days after feeding, half of the carp from each group were intubated with 10 9 colony-forming units (CFU) of a pathogenic strain of A. hydrophila. Gut samples were taken 12 hr to 7 days after application and analysed using microbiological and molecular biological techniques (NGS, RT-PCR-DGGE). The reaction of the mucosa and the microbiota to an A. hydrophila intubation differed in carp fed with β-glucan compared to carp from the control group. In β-glucan fed carp, the total bacterial amount was lower but the number of bacterial species was higher. Bacterial composition was different for carp from both treatment groups. The number of mucin filled goblet cells was reduced in carp fed the β-glucan diet. Mucus was obviously released from the goblet cells and was probably washed out of the gut together with high numbers of bacteria. This might be protective against pathogenic bacteria and, therefore, feeding with β-glucan may provide protection against infections of the gut in carp., (© 2018 John Wiley & Sons Ltd.)

β-glucans are immunomodulants that are used in fish nutrition for health improvement. The effect of MacroGard®, a commercially available β-1,3/1,6-glucan, on the bacterial community in the gut of common carp ( Cyprinus carpio) was examined focusing on species diversity. Separate segments of the gut were analysed. We identified cultured bacteria isolates by analysing 16S rRNA gene sequences and additionally used reverse transcription polymerase chain reaction-denaturing gradient gel electrophoresis ( RT- PCR- DGGE) for examination of bacterial diversity. With both methods, we could detect a significantly higher amount of bacterial operational taxonomic units ( OTUs) in all examined parts of the gut after feeding with MacroGard®. Independent of the feeding regime, mostly motile aeromonads, pseudomonads and Vibrio sp. could be detected in the intestinal community of carp. Shewanella putrefaciens and Vibrio sp. were regular components of the intestinal microflora but were present to a lesser extent in the microbial community of carp fed with MacroGard®. This could have a positive effect for fish health and also in respect of food safety for fish destined for human consumption. Our results suggest that feeding of MacroGard® results in a more diverse intestinal community that could help to prevent the invasion and establishment of pathogenic micro-organisms. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the impact of beta-glucan feeding on the regulation of microRNA expression of claudin genes and the prevention of an intestinal inflammatory response post Aeromonas hydrophila intubation in common carp. The response of the gut epithelium to bacterial challenges following beta-glucan feeding is outlined. The benefits of beta-glucan supplementation in the cultivation of carp are discussed.