Listeria monocytogenes is a ubiquitous, saprophytic, Gram-positive bacterium and occasional food-borne pathogen, often associated with ready-to-eat meat products, according to University of Arkansas researchers, S.R. Milillo and colleagues. In the latest issue of Poultry Science, they explain that, because of the increased consumer interest in organic, all-natural and free-range poultry products, it is important to understand L. monocytogenes in the context of such systems.

Pasture-reared poultry were surveyed over the course of two eight-week rearing periods. Caecal, soil and grass samples were collected for Listeria isolation and characterization.

Seven of 399 caecal samples (or 1.75 per cent) were Listeria-positive. All positive caecal samples were obtained from broilers sampled at two weeks of age.

Grass and soil samples were collected from the pasture both before and after introduction of the poultry. Environmental samples collected after introduction of poultry were significantly more likely to contain Listeria.

The results of analytical profile index Listeria, sigB allelic typing, and hlyA PCR tests found that both L. monocytogenes and L. innocua, including haemolytic L. innocua, were recovered from the caecal and environmental (grass/soil) samples. The sigB allelic typing also revealed that:

1. positive samples could be composed of two or more allelic types
2. allelic types found in caecal samples could also be found in the environment, and
3. allelic types could persist through the two rearing periods.

The Arkansas researchers say their data indicate that both pasture-reared poultry and their environment can be contaminated with L. monocytogenes and haemolytic L. innocua.

Reference

Milillo S.R., J.C. Stout, I.B. Hanning, A. Clement, E.D. Fortes, H.C. den Bakker, M. Wiedmann and S.C. Ricke. 2012. Listeria monocytogenes and hemolytic Listeria innocua in poultry. Poult. Sci., 91(9):2158-2163. doi: 10.3382/ps.2012-02292

Further Reading You can view the full report (fee payable) by clicking here.