This is the first evidence that a gene encoding a Dps protein is transcribed together with downstream genes. As mentioned above, the role of Fri in the stress response and virulence is well established, but the functions of Lmo0944 and Lmo0945 and their potential roles in these processes in L. monocytogenes are currently unknown and will be the subject of future studies. Similarly, further research

effort is required in order to clarify the potential role of the other identified penicillin G-inducible genes in tolerance and/or susceptibility of L. monocytogenes to β-lactam antibiotics. Conclusions Disease outbreaks caused by L. monocytogenes-contaminated foods and the serious illnesses and fatalities that occur in susceptible individuals highlight the importance of understanding the mechanisms GW-572016 supplier that enable this bacterium to survive antibiotic therapy. The present study resulted in the identification of ten penicillin G-inducible genes of L. monocytogenes. In-depth examination of the contribution of three of the identified genes, namely fri, phoP and axyR, to the susceptibility and tolerance of L. monocytogenes PF-3084014 chemical structure to β-lactams indicated that the regulators PhoP and AxyR do not play a significant role in these reactions. However, these proteins are probably involved in

transmitting signals to adjust the rate of growth of L. monocytogenes under β-lactam pressure. The most important finding of this research is that the ferritin-like protein Fri contributes to L. monocytogenes tolerance of the β-lactam antibiotics penicillin G and ampicillin – the current drugs of choice for Sirolimus datasheet the treatment of listeriosis – as well as to the high innate resistance of this bacterium to some cephalosporins. It is therefore

possible that the functions of Fri are essential for the survival of L. monocytogenes in the clinical setting. In light of the key role of L. monocytogenes Fri, both in the response to multiple stresses and during infection in vivo, it may represent an attractive target for the development of improved control and treatment strategies for this important pathogen. Methods Bacterial strains, media, plasmids and DNA techniques Escherichia coli strain DH5α used in cloning experiments was grown on Luria-Bertani medium. The L. monocytogenes EGD (serotype 1/2a) wild-type strain was kindly provided by S.J. Foster, University of Sheffield, United Kingdom. Isogenic EGDΔhly, EGDΔphoP and EGDΔaxyR deletion mutants were constructed in this study (described in detail below), while the isogenic EGDΔfri deletion mutant was a generous gift from Hanne Ingmer, Royal Veterinary and Agricultural University, Denmark. L. monocytogenes strains were grown in brain heart infusion (BHI) broth medium (Oxoid). L.