Occurrence of Listeria spp. in mattress dust of farm children in Bavaria.

Several epidemiological studies have shown that the farm environment impacts allergy protection mechanisms in children. These associations are not well understood, but it is thought that contact to microorganisms may mediate this effect. For example, heat-inactivated Listeria (L.) monocytogenes have been successfully used as an adjuvant in mouse immunotherapy to modulate airway hyperreactivity and inflammation. In investigating the link between farming lifestyle and prevention of childhood allergy, we examined the prevalence of Listeria spp. in dust specimens from the environment of rural children. A total of 26 farms located in Bavaria (South Germany) were examined. Dust samples taken from mattresses (n=63), cow-sheds (n=30) and swine-sheds (n=10) were qualitatively screened for the presence of viable Listeria spp. according to the ISO 11290-1 method and additionally by L. monocytogenes specific iap-based real-time PCR. Isolates were further characterized by biochemical techniques, serology and multiplex PCR. Nineteen of 26 farms tested positive for Listeria spp. and seven were tested negative. The dominant species found by culturing methods were L. innocua (n=12) and L. monocytogenes (n=8). Viable Listeria spp. were detected in 8% of the mattress dust samples, whereas real-time PCR revealed 60% L. monocytogenes positive specimens. Regarding animal sheds, 28% of dust samples showed viable Listeria spp., while using real-time PCR found that 28% of specimens were L. monocytogenes positive. All strains of L. monocytogenes except one (4ab) belonged to the serotype 1/2a. Our data demonstrate that a substantial number of farm children's beds contain L. monocytogenes. The importance of this result regarding the health of children must be evaluated by epidemiological investigations on both the risk of listeriosis and the effects on protection against allergies.