A common adaptation among several highly host-adapted Gram-negative species from the Pasteurellaceae, Neisseriaceae, and Moraxellaceae families that exclusively reside in the upper respiratory tract is the ability to directly bind host transferrin (Tf) and use it as a source of iron for growth (1, 2). Iron-loaded transferrin is captured by surface receptors that remove iron from Tf and transport the iron across the outer membrane, where it is subsequently transported into the cell through a periplasm binding protein-dependent ABC (ATP binding cassette) transport system. Early observations that the interaction of the bacterial receptors with Tf was highly host specific (3-5) provided a rational explanation for the strict host specificity of these bacterial pathogens.The initial capture of iron-loaded Tf is mediated by a surface lipoprotein, Tf binding protein B (TbpB), which consists of two structurally equivalent lobes preceded by a relatively long anchoring peptide that would allow the protein to extend far from the outer membrane surface (6). The role of TbpB is to capture the iron-loaded form of Tf and deliver it to Tf binding protein A (TbpA), the integral outer membrane protein that serves as the channel for transporting iron across the outer membrane. The structure of a Tf-TbpB complex has recently been determined (7), revealing that that the process of binding iron-loaded Tf does not involve substantial changes in the conformation of the TbpB Nlobe or the Tf C-lobe and effectively traps the Tf C-lobe in the iron-loaded state. In contrast, binding of Tf to TbpA involves substantial conformational changes in the TbpB C-lobe, resulting in substantial separation of the C1 and C2 domains that both contribute ligands for coordination of iron (8). In the absence of structural information for TbpA alone one can only speculate on the conformational changes that occur in the surface loop structures of TbpA upon binding Tf.The process by which TbpB mediates the initial capture of iron-loaded Tf and transfers it to TbpA is only partly understood. The variable association of the anchoring peptide with the C-lobe (9) and its requirement for formation of the ternary complex (10) may indicate that modulation of the anchor peptide may be involved. Although structural models can be developed for the ternary complex (2, 8), these are not based on high-resolution structural information for the actual complex, and how TbpB maintains an interaction with Tf upon domain separation is still not resolved. Similarly, the process by which iron is released and transported across the outer membrane and the degree to which different regions of TbpB participate in this process is uncertain.Since the first discovery of the bacterial Tf receptors (11, 12) and the demonstration of their exquisite host specificity (4), they were postulated to be essential for survival in the native host and thus potentially ideal vaccine targets. The importance of the receptor proteins has been confirmed in a male gonococcal infection

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A total of 229 Spanish Actinobacillus pleuropneumoniae isolates recovered from diseased pigs with pleuropneumonia from 1997 to 2004 was tested for their susceptibility to 11 antimicrobials in a broth microdilution method. All the isolates were susceptible to florfenicol and most of them to cephalothin; however, a high rate of resistance was observed to tetracycline. A bimodal or multimodal distribution of isolates over the MIC range were observed for penicillins, tetracycline, trimethoprim, sulfisoxazole and nalidixic acid, suggesting the development of acquired resistance. Eight resistance patterns were established, and 21.1% of the isolates were resistant to at least two antimicrobials. In addition, a considerable increase in the resistance to tetracyclines was observed during the last decade in Spain, when compared with other A. pleuropneumoniae strains isolated during 1987-1988 (Gutiérrez, C.B., Píriz, S., Vadillo, S., Rodríguez Ferri, E.F., 1993. In vitro susceptibility of Actinobacillus pleuropneumoniae strains to 42 antimicrobial agents. Am. J. Vet. Res. 54, 546-550); this finding was also observed for gentamicin in minor percentage.

Ceftiofur, florfenicol, and enrofloxacin are recommended for treatment of infections caused by P multocida subsp multocida in Spain. Increased frequency of resistance to oxytetracycline and sulfonamide drugs may be a contraindication for their use.

A Chlamydophila abortus-induced abortion model was carried out on the basis of the experimental infection of ewes at day 75 of gestation. The infection induced abortions and the birth of weak lambs during the last 3 weeks of pregnancy. To study the kinetics of the infection in the placenta and in other organs, infected ewes were killed at 105, 120, and 130 days of gestation and also several days after abortion or parturition. Infected ewes developed a systemic infection that caused a mild and transient pneumonia and focal hepatitis. Pathologic changes were observed in placentas at 120 day of gestation, although the lesions varied between animals and even between placentomes of the same placenta. The first placental area infected was the maternal stroma and epithelium next to the intercaruncular areas, where neutrophilic response seemed to control the infection. A substantial degree of multiplication of C. abortus was then observed in the trophoblast cells of the placentome, periplacentomal choriallantoic membranes, and hilius, with an inflammatory exudate composed mainly of neutrophils, some macrophages, and very scarce lymphocytes. After abortion, the lesions affected the intercotyledonary areas of the aborted placentas, whereas in the uterus significant lymphocyte infiltration was observed, together with a rapid decrease of the C. abortus antigen in the degenerated caruncular tissues.