Feeding of β-1,3/1,6-glucan increases the diversity of the intestinal microflora of carp (Cyprinus carpio)

beta-glucans are immunomodulants that are used in fish nutrition for health improvement. The effect of MacroGard (R), a commercially available beta-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 (R). 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 (R). 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 (R) results in a more diverse intestinal community that could help to prevent the invasion and establishment of pathogenic micro-organisms.