Brucella Ornithine Lipids Figure 4. B. abortus OL-deficient mutants do not trigger increased blood or peritoneal leukocyte responses during the early stages of infection in mice. Mice were intraperitoneally injected with 106 CFU of BAB-parental or BABDolsB or with 105 CFU of S. typhimurium, total leukocyte numbers determined at the indicated periods and values normalized with respect to the values in mice inoculated with PBS. Asterisks indicate significant differences between S. typhimurium and the control (no significant differences were observed for the B. abortus strains). doi:10.1371/journal.pone.0016030.g004 These results clearly show that Brucella OL, in contrast to those of B. pertussis, do not bear a marked PAMP. In addition, they demonstrate that Brucella phospholipids do not inhibit PAMP recognition. Discussion The OM of most gram negative bacteria hinders the penetration of harmful molecules, and the LPS plays a key role in this important property. The LPS inner sections (core oligosaccharide and lipid A) are rich in acidic sugars and orthophosphate, and these negatively charged groups bind divalent cations and polyamines that bridge the LPS molecules and hamper the partition of hydrophobic permeants into the OM [37,38]. However, this supramolecular arrangement makes OM sensitive to divalent cation chelators like EDTA and to bactericidal peptides. Moreover, this set of properties is connected to the PAMP of a variety of OM molecules, primarily the LPS. Interestingly, Brucella OM is comparatively permeable to hydro- phobic compounds and resistant to those agents. At least in part, these properties are accounted for by a low number of negatively Figura 5. The OL-deficiency does alter not alter the profiles of lymphocytes, neutrophils and monocytes during the early stages of B. abortus infection in mice. Lymphocyte, neutrophil and monocyte number is (A) blood and (B) peritoneum of mice intraperitoneally injected with 106 CFU of BAB-parental or BABDolsB (values normalized with respect to the values in mice inoculated with PBS). doi:10.1371/journal.pone.0016030.g005 PLoS ONE | www.plosone.org 5 January 2011 | Volume 6 | Issue 1 | e16030