Explaining Salmonella Survival in the Feed Mill

NORWAY - Researchers investigating the factors affecting the survival of Salmonella in feed mills and fish meal factories found that cellulose was not an important factor in the biofilm matrix but that the different colony shapes affect persistence after drying and nutrient depletion in the biofilm.

25 November 2009

3 minute read

Europe

In their paper in BMC Veterinary Research, Vestby and co-authors explain that biofilm has been shown to be one way for Salmonella to persist in the feed factory environment.

Matrix components, such as fimbriae and cellulose, have been suggested to play an important role in the survival of Salmonella in the environment. Multicellular behaviour by Salmonella is often categorised according to colony morphology into rdar (red, dry and rough) expressing curli fimbriae and cellulose, bdar (brown, dry and rough) expressing curli fimbriae and pdar (pink, dry and rough) expressing cellulose.

The researcher said that the aim of the study was to look into the distribution of morphotypes among feed and fish meal factory strains of Salmonella, with emphasis on potential differences between morphotypes with regards to survival in the feed factory environment.

Results

When screening a total of 148 Salmonella ser. Agona, Salmonella ser. Montevideo, Salmonella ser. Senftenberg and Salmonella ser. Typhimurium strains of feed factory, human clinical and reference collection origin, as many as 99 per cent were able to express rough morphology (rdar or bdar).

The dominant morphotype was rdar (74 per cent) but as many as 55 per cent of Salmonella ser. Agona and 19 per cent of Salmonella ser. Senftenberg displayed the bdar morphology.

Inconsistency in Calcofluor binding, indicating expression of cellulose, was found among 25 per cent of all the strains tested but Salmonella ser. Agona showed to be highly consistent in Calcofluor binding (98 per cent).

In biofilm, Salmonella ser. Agona strains with bdar morphology was found to be equally tolerant to disinfection treatment as strains with rdar morphotype. However, rdar morphology appeared to be favourable in long-term survival in biofilm in a very dry environment. Chemical analysis showed no major differences in polysaccharide content between bdar and rdar strains.

The researchers said their results indicate that cellulose is not a major component of the Salmonella biofilm matrix.

Conclusions

The bdar morphotype is common among Salmonella ser. Agona strains isolated from the factory environment. The rdar and the bdar strains were found to be equally tolerant to disinfectants, while the rdar strain was found to be more tolerant to long-term desiccation and nutrient depletion in biofilm than the bdar strain.

Cellulose does not appear to be a major component of the Salmonella biofilm matrix.

Reference

Vestby L.K., T. Moretro, S. Ballance, S. Langsrud and L.L. Nesse. 2009. Survival potential of wild type cellulose deficient Salmonella from the feed industry. BMC Veterinary Research. 2009, 5:43 doi:10.1186/1746-6148-5-43