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Negative plant-soil feedbacks can impair seedling survival near conspecific trees and may enhance forest diversity. However, the reciprocal aspect of this relationship, the influence of tree diversity on the strengths of plant-soil feedbacks is unknown. We examined whether tree diversity can affect plant-soil feedbacks of two common temperate tree species, beech (Fagus sylvatica) and sessile oak (Quercus petraea). Soils were collected from adjacent to beech and oak trees growing in a manipulative tree diversity field experiment and used as inocula in a greenhouse experiment to determine whether increasing tree diversity could moderate the strengths of plant-soil feedbacks. We also compared plant-soil feedback responses between Q. petraea and F. sylvatica to test the hypothesis that stronger negative feedbacks contribute to the relative rarity of Q. petraea. Negative plant-soil feedbacks on seedling emergence were observed for both tree species. Emergence increased with increasing distance of the soil inocula from established trees in the field, but only for inocula taken from the low diversity treatment (monocultures) and irrespective of the inoculum source (i.e. from conspecific vs. heterospecific trees). In contrast, tree diversity had no influence on the biomass responses of seedlings for either tree species. Quercus petraea seedlings experienced negative plant-soil feedbacks in their biomass responses which cascaded up to higher trophic levels, i.e. leaf pathogen infection. Fagus sylvatica biomass responses suggested positive plant-soil feedbacks, supporting the hypothesis that the abundance of this species is less limited by interactions with natural enemies. Our results suggest that distance-dependent seedling emergence in temperate forests may depend on the diversity of tree communities and that plant-soil feedbacks may cascade up to higher trophic levels and change with the life history stage of the seedlings involved. An increased focus on the surrounding c

In a previous study, we showed that coagulase positive staphylococci (CPS), which are often used as indicators for S. aureus, are frequently found on pig carcasses at slaughter. Further characterization of the CPS identified only a minor part as S. aureus. Selected non-S. aureus strains were all identified as S. hyicus, However, two studies have described also in this species strains that produce staphylococcal enterotoxins. The aim of the present study was therefore to further characterize such coagulase positive S. hyicus strains isolated from pig carcasses and to assess the results also in view of their food safety relevance. A total of 189 S. hyicus strains from abattoirs A (n=36) and B (n=153) were characterized. Phenotypically, 98.9% showed non-pigmented colonies, 99.5% no haemolysis and 67.7% were egg yolk-positive. DNase activity was found in all but one isolate. Only five of the 189 strains were resistant to the antimicrobials tested. One strain harboured the mecA gene. Exfoliative toxin genes were detected in 31 (16.4%) strains. Six strains harboured the exhA and 25 strains the exhD gene. S. aureus Enterotoxin (SE) genes were detected in none of the strains. The PFGE genotyping results show only a limited number of clusters. Cluster I included more than 50% of the strains. The fact that similar or closely related PFGE patterns of S. hyicus can be found on carcasses after bleeding in both abattoirs indicates the occurrence of widespread strains in the Swiss pig population. Moreover, the genotyping results revealed a remarkable homogeneity in S. hyicus strains isolated from different slaughter process stages in abattoir B, which could indicate a recontamination problem with persisting strains.

Shiga toxin producing Escherichia coli (STEC) harbouring the stx2d-activatable gene and expressing the mucus- and elastase-activatable phenotype have been associated with severe outcomes of human disease. However, there is limited data available on the occurrence of such strains in livestock reservoirs. In this study, we analyzed 11 STEC strains isolated from healthy cattle and sheep at slaughter that were originally detected to contain the stx2c allele, for the presence of the stx2d-activatable genotype. Ten of the 11 strains displayed the stx2d-activatable genotype as determine by PstI restriction fragment length polymorphism (RFLP) of 890-bp fragments of their stx genes. However, only in six of 10 strains whose stx genes were sequenced, the presence of stx2d-activatable could be confirmed based on the predicted amino acid sequence of their StxA subunits; the remaining four strains contained Stx2c A subunit. Five of the six strains which contained stx2d-activatable displayed the activatable phenotype on Vero cells. Genes for adhesins such as the outer membrane protein intimin (eae), which is essential for the intimate attachment and the formation of attaching-and-effacing lesions on intestinal epithelial cells, or the STEC autoagglutinating adhesin (saa), potentially important in eae-negative STEC, were not detected. Moreover, all the strains tested negative for EHEC-hlyA encoding enterohaemorrhagic E. coli (EHEC) hemolysin. To our knowledge, this is the first study that reports the presence of STEC harbouring stx2d-activatable and producing the activatable Stx2d in fecal samples of sheep. Therefore both cattle and sheep are reservoirs of such strains and potential sources of human infections. This is of particular importance, because in contrast to other eae-negative STEC, strains producing Stx2dactivatable may cause severe diseases such as bloody diarrhoea and haemolytic uremic syndrome in humans.

BACKGROUND: Enterobacter sakazakii is a foodborne pathogen that has been associated with sporadic cases and outbreaks causing meningitis, necrotizing enterocolitis and sepsis especially in neonates. The current FDA detection method includes two enrichment steps, the subculturing of the second enrichment broth on a selective agar (VRBG), a further subculturing of selected grown colonies on TSA and the subsequent biochemical identification of yellow-pigmented colonies by API20E. However, there is a strong need for simplified methods for isolation and identification of E. sakazakii. In this study, two chromogenic media, which allow to indicate presumptive E. sakazakii colonies by the alpha glucosidase activity, as well as a newly developed 1,6-alpha-glucosidase based conventional PCR assay and a rRNA oligonucleotide probe based commercial test system for identification of presumptive E. sakazakii were evaluated on 98 target and non-target strains. The methods were compared with respect to specificity aspects. RESULTS: A total of 75 presumptive E. sakazakii and 23 non-target strains were analysed by using chromogenic media, alpha-glucosidase based PCR assay, and the VIT assay. For most presumptive E. sakazakii strains on the chromogenic media, the PCR and VIT assay confirmed the identification. However, for a number of presumptive E. sakazakii isolates from fruit powder, the alpha-glucosidase PCR and VIT assay did not correspond to the typical E. sakazakii colonies on DFI and ESIA. Further characterization by API32E identification, phylogenetic analysis of partial 16S rRNA sequences and ribotyping strongly suggested, that these strains did not belong to the species E. sakazakii. The newly developed alpha-glucosidase based PCR assay as well as the commercially available VIT Enterobacter sakazakii identification test showed an excellent correlation with the 16S rRNA data, and are thus well suited for identification of E. sakazakii. CONCLUSION: The results indicate that pr