Actinobacillus pleuropneumoniae (App) is a Gram-negative bacterium that causes porcine pleuropneumonia, leading to economic losses in the swine industry. Due to bacterial resistance to antibiotics, new treatments for this disease are currently being sought. Lactoferrin (Lf) is an innate immune system glycoprotein of mammals that is microbiostatic and microbicidal and affects several bacterial virulence factors. The aim of this study was to investigate whether bovine iron-free Lf (BapoLf) has an effect on the growth and virulence of App. Two serotype 1 strains (reference strain S4074 and the isolate BC52) and a serotype 7 reference strain (WF83) were analyzed. First, the ability of App to grow in iron-charged BLf was discarded because in vivo, BapoLf sequesters iron and could be a potential source of this element favoring the infection. The minimum inhibitory concentration of BapoLf was 14.62, 11.78 and 10.56 µM for the strain BC52, S4074 and WF83, respectively. A subinhibitory concentration (0.8 µM) was tested by assessing App adhesion to porcine buccal epithelial cells, biofilm production, and the secretion and function of toxins and proteases. Decrease in adhesion (24-42 %) was found in the serotype 1 strains. Biofilm production decreased (27 %) for only the strain 4074 of serotype 1. Interestingly, biofilm was decreased (60-70 %) in the three strains by BholoLf. Hemolysis of erythrocytes and toxicity towards HeLa cells were not affected by BapoLf. In contrast, proteolytic activity in all strains was suppressed in the presence of BapoLf. Finally, oxytetracycline produced synergistic effect with BapoLf against App. Our results suggest that BapoLf affects the growth and several of the virulence factors in App.

Iron is an essential nutrient for the survival of pathogens inside a host. As a general strategy against microbes, mammals have evolved complex iron-withholding systems for efficiently decreasing the iron accessible to invaders. Pathogens that inhabit the respiratory, intestinal and genitourinary tracts encounter an iron-deficient environment on the mucosal surface, where ferric iron is chelated by lactoferrin, an extracellular glycoprotein of the innate immune system. However, parasitic protozoa have developed several mechanisms to obtain iron from host holo-lactoferrin. Tritrichomonas fetus, Trichomonas vaginalis, Toxoplasma gondii and Entamoeba histolytica express lactoferrin-binding proteins and use holo-lactoferrin as an iron source for growth in vitro; in some species, these binding proteins are immunogenic and, therefore, may serve as potential vaccine targets. Another mechanism to acquire lactoferrin iron has been reported in Leishmania spp. promastigotes, which use a surface reductase to recognize and reduce ferric iron to the accessible ferrous form. Cysteine proteases that cleave lactoferrin have been reported in E. histolytica. This review summarizes the available information on how parasites uptake and use the iron from lactoferrin to survive in hostile host environments.

Mannheimia haemolytica is a Gram negative bacterium that is part of the bovine respiratory disease, which causes important economic losses in the livestock industry. In the present work, the interaction between M. haemolytica A1 and bovine lactoferrin (BLf) was studied. This iron-chelating glycoprotein is part of the mammalian innate-immune system and is present in milk and mucosal secretions; Lf is also contained in neutrophils secondary granules, which release this glycoprotein at infection sites. It was evidenced that M. haemolytica was not able to use iron-charged BLf (BholoLf) as a sole iron source; nevertheless, iron-lacked BLf (BapoLf) showed a bactericidal effect against M. haemolytica with MIC of 4.88 ± 1.88 and 7.31 ± 1.62 μM for M. haemolytica strain F (field isolate) and M. haemolytica strain R (reference strain), respectively. Through overlay assays and 2-D electrophoresis, two OMP of 32.9 and 34.2 kDa with estimated IP of 8.18 and 9.35, respectively, were observed to bind both BapoLf and BholoLf; these OMP were identified by Maldi-Tof as OmpA (heat-modifiable OMP) and a membrane protein (porin). These M. haemolytica BLf binding proteins could be interacting in vivo with both forms of BLf depending on the iron state of the bovine.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-016-0378-1) contains supplementary material, which is available to authorized users.

Lactoferrin (Lf) is an iron-chelating glycoprotein present in milk and mucosal secretions, a component of the mammalian innate immune system. Lf is microbiostatic and microbicidal. Lf can reduce the bacterial expression of virulence factors, such as those involved in biofilm production and protease secretion. The high identity among mammalian Lf sequences facilitates its use in human and veterinary medicine. Lf of bovine origin is the principal Lf used due to its commercial availability through purification from milk whey; recombinant Lfs (bovine, human, and porcine) have been used as well. Lf is a stable protein that retains its physicochemical characteristics under gastric pH conditions, and in most cases it is bioactive even after digestion; thus, the incorporation of Lf into diets facilitates its administration to animals. The aim of this review is to examine original research in which the effects of bovine and porcine Lf on pathogens of domestic animals have been demonstrated through in vitro and in vivo assays, with the purpose of ascertaining the benefits that Lf provides in the treatment of infectious diseases.

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