Listeria spp. in broiler flocks: recovery rates and species distribution investigated by conventional culture and the EiaFoss method

The occurrence of Listeria monocytogenes in samples from broiler houses and cloacal swabs taken at the abattoir was investigated. An automated immunobased method (EiaFoss) was used, and 42 samples were also analysed by conventional culture; both methods were based on a two-step selective enrichment using CHR.4.17; Fraser and Fraser broths. L. monocytogenes was isolated from two of 71 broiler flocks, yielding an estimated flock prevalence of 3%. The flock prevalence of L. inocua was estimated to 13%, and it was speculated that the potential of this apathogenic bacteria to grow faster than L. monocytogenes in enrichment broths may lead to an underestimation of the prevalence of L. monocytogenes. Furthermore, as L. inocua was also detected by the EiaFoss method, a significant amount of bacterial confirmation work had to be done. Of 42 samples analysed by conventional culture, four yielded L. inocua, of which two were not positive by EiaFoss.