Binding of Actinobacillus pleuropneumoniae to phosphatidylethanolamine

Actinobacillus pleuropneumoniae: The molecular determinants of virulence and pathogenesis

Actinobacillus pleuropneumoniae, the causative agent of porcine pleuropneumonia, is responsible for high economic losses in swine herds across the globe. Pleuropneumonia is characterized by severe respiratory distress and high mortality. The knowledge about the interaction between bacterium and host within the porcine respiratory tract has improved significantly in recent years. A. pleuropneumoniae expresses multiple virulence factors, which are required for colonization, immune clearance, and tissue damage. Although vaccines are used to protect swine herds against A. pleuropneumoniae infection, they do not offer complete coverage, and often only protect against the serovar, or serovars, used to prepare the vaccine. This review will summarize the role of individual A. pleuropneumoniae virulence factors that are required during key stages of pathogenesis and disease progression, and highlight progress made toward developing effective and broadly protective vaccines against an organism of great importance to global agriculture and food production.

Incorporation of Actinobacillus pleuropneumoniae in Preformed Biofilms by Escherichia coli Isolated From Drinking Water of Swine Farms

Actinobacillus pleuropneumoniae, the etiological agent of porcine pleuropneumonia, represents one of the most important health problems in the swine industry worldwide and it is included in the porcine respiratory disease complex. One of the bacterial survival strategies is biofilm formation, which are bacterial communities embedded in an extracellular matrix that could be attached to a living or an inert surface. Until recently, A. pleuropneumoniae was considered to be an obligate pathogen. However, recent studies have shown that A. pleuropneumoniae is present in farm drinking water. In this study, the drinking water microbial communities of Aguascalientes (Mexico) swine farms were analyzed, where the most frequent isolated bacterium was Escherichia coli. Biofilm formation was tested in vitro; producing E. coli biofilms under optimal growth conditions; subsequently, A. pleuropneumoniae serotype 1 (strains 4074 and 719) was incorporated to these biofilms. Interaction between both bacteria was evidenced, producing an increase in biofilm formation. Extracellular matrix composition of two-species biofilms was also characterized using fluorescent markers and enzyme treatments. In conclusion, results confirm that A. pleuropneumoniae is capable of integrates into biofilms formed by environmental bacteria, indicative of a possible survival strategy in the environment and a mechanism for disease dispersion.

Type IV fimbrial subunit protein ApfA contributes to protection against porcine pleuropneumonia

Porcine pleuropneumonia caused by Actinobacillus pleuropneumoniae accounts for serious economic losses in the pig farming industry worldwide. We examined here the immunogenicity and protective efficacy of the recombinant type IV fimbrial subunit protein ApfA as a single antigen vaccine against pleuropneumonia, or as a component of a multi-antigen preparation comprising five other recombinant antigens derived from key virulence factors of A. pleuropneumoniae (ApxIA, ApxIIA, ApxIIIA, ApxIVA and TbpB). Immunization of pigs with recombinant ApfA alone induced high levels of specific serum antibodies and provided partial protection against challenge with the heterologous A. pleuropneumoniae serotype 9 strain. This protection was higher than that engendered by vaccination with rApxIVA or rTbpB alone and similar to that observed after immunization with the tri-antigen combination of rApxIA, rApxIIA and rApxIIIA. In addition, rApfA improved the vaccination potential of the penta-antigen mixture of rApxIA, rApxIIA, rApxIIIA, rApxIVA and rTbpB proteins, where the hexa-antigen vaccine containing rApfA conferred a high level of protection on pigs against the disease. Moreover, when rApfA was used for vaccination alone or in combination with other antigens, such immunization reduced the number of pigs colonized with the challenge strain. These results indicate that ApfA could be a valuable component of an efficient subunit vaccine for the prevention of porcine pleuropneumonia.

Virulence factors of Actinobacillus pleuropneumoniae involved in colonization, persistence and induction of lesions in its porcine host

Actinobacillus pleuropneumoniae is the causative agent of porcine pleuropneumonia. The virulence factors of this microorganism involved in colonization and the induction of lung lesions have been thoroughly studied and some have been well characterized. A. pleuropneumoniae binds preferentially to cells of the lower respiratory tract in a process involving different adhesins and probably biofilm formation. Apx toxins and lipopolysaccharides exert pathogenic effects on several host cells, resulting in typical lung lesions. Lysis of host cells is essential for the bacterium to obtain nutrients from the environment and A. pleuropneumoniae has developed several uptake mechanisms for these nutrients. In addition to persistence in lung lesions, colonization of the upper respiratory tract – and of the tonsils in particular – may also be important for long-term persistent asymptomatic infection. Information on virulence factors involved in tonsillar and nasal cavity colonization and persistence is scarce, but it can be speculated that similar features as demonstrated for the lung may play a role.

Host-pathogen interactions of Actinobacillus pleuropneumoniae with porcine lung and tracheal epithelial cells

Host-pathogen interactions are of great importance in understanding the pathogenesis of infectious microorganisms. We developed in vitro models to study the host-pathogen interactions of porcine respiratory tract pathogens using two immortalized epithelial cell lines, namely, the newborn pig trachea (NPTr) and St. Jude porcine lung (SJPL) cell lines. We first studied the interactions of Actinobacillus pleuropneumoniae, an important swine pathogen, using these models. Under conditions where cytotoxicity was absent or low, we showed that A. pleuropneumoniae adheres to both cell lines, stimulating the induction of NF-kappaB. The NPTr cells consequently secrete interleukin 8, while the SJPL cells do not, since they are deprived of the NF-kappaB p65 subunit. Cell death ultimately occurs by necrosis, not apoptosis. The transcriptomic profile of A. pleuropneumoniae was determined after contact with the porcine lung epithelial cells by using DNA microarrays. Genes such as tadB and rcpA, members of a putative adhesin locus, and a gene whose product has high homology to the Hsf autotransporter adhesin of Haemophilus influenzae were upregulated, as were the genes pgaBC, involved in biofilm biosynthesis, while capsular polysaccharide-associated genes were downregulated. The in vitro models also proved to be efficient with other swine pathogens, such as Actinobacillus suis, Haemophilus parasuis, and Pasteurella multocida. Our results demonstrate that interactions of A. pleuropneumoniae with host epithelial cells seem to involve complex cross talk which results in regulation of various bacterial genes, including some coding for putative adhesins. Furthermore, our data demonstrate the potential of these in vitro models in studying the host-pathogen interactions of other porcine respiratory tract pathogens.

Is lipopolysaccharide a factor in infectivity of Chlamydia trachomatis?

Lipopolysaccharide (LPS) is a major surface component of Chlamydia trachomatis, as with all Gram-negative bacteria. The effect of C. trachomatis LPS on C. trachomatis infectivity of human epithelial cells was investigated. C. trachomatis LPS and C. trachomatis LPS antibody significantly reduced infectivity, mostly in a dose-dependent manner. As the structure of LPS in C. trachomatis is simple and consists only of lipid A and 3-deoxy-D-manno-octulosonic acid (Kdo), we investigated whether lipid A or Kdo was inhibitory to chlamydial infectivity. Polymyxin B, as a lipid A inhibitor, and Kdo considerably reduced C. trachomatis infectivity. With all the LPS inhibitors used, there was greater inhibition against serovar E than serovar LGV. These results suggest a role for LPS in chlamydial infectivity. Elucidation of how LPS acts in infectivity and identification of host-cell receptors would help in understanding pathogenicity.

Binding of Clostridium botulinum type C and D neurotoxins to ganglioside and phospholipid. Novel insights into the receptor for clostridial neurotoxins

Clostridium botulinum neurotoxins (BoNTs) act on nerve endings to block acetylcholine release. Their potency is due to their enzymatic activity and selective high affinity binding to neurons. Although there are many pieces of data available on the receptor for BoNT, little attempt has been made to characterize the receptors for BoNT/C and BoNT/D. For this purpose, we prepared the recombinant carboxyl-terminal domain of the heavy chain (H(C)) and then examined its binding capability to rat brain synaptosomes treated with enzymes and heating. Synaptosomes treated with proteinase K or heating retained binding capability to both H(C)/C and H(C)/D, suggesting that a proteinaceous substance does not constitute the receptor component. We next performed a thin layer chromatography overlay assay of H(C) with a lipid extract of synaptosomes. Under physiological or higher ionic strengths, H(C)/C bound to gangliosides GD1b and GT1b. These data are in accord with results showing that neuraminidase and endoglycoceramidase treatment decreased H(C)/C binding to synaptosomes. On the other hand, H(C)/D interacted with phosphatidylethanolamine but not with any ganglioside. Using cerebellar granule cells obtained from GM3 synthase knock-out mice, we found that BoNT/C did not elicit a toxic effect but that BoNT/D still inhibited glutamate release to the same extent as in granule cells from wild type mice. These observations suggested that BoNT/C recognized GD1b and GT1b as functional receptors, whereas BoNT/D induced toxicity in a ganglioside-independent manner, possibly through binding to phosphatidylethanolamine. Our results provide novel insights into the receptor for clostridial neurotoxin.

Surface polysaccharides and iron-uptake systems of Actinobacillus pleuropneumoniae

Actinobacillus pleuropneumoniae is the etiologic agent of porcine pleuropneumonia. Infection by A. pleuropneumoniae is a multifactorial process governed by many virulence factors acting alone or, more often, in concert to establish the pathogen in the porcine host. The aim of this short review is to present recent data concerning important surface molecules of A. pleuropneumoniae; namely, lipopolysaccharides, capsular polysaccharides, and a subset of outer membrane proteins involved in iron uptake.

Applications of the ninhydrin reaction for analysis of amino acids, peptides, and proteins to agricultural and biomedical sciences

The reaction of ninhydrin with primary amino groups to form the purple dye now called Ruhemann's purple (RP) was discovered by Siegfried Ruhemann in 1910. In addition, imines such as pipecolic acid and proline, the guanidino group of arginine, the amide groups of asparagine, the indole ring of tryptophan, the sulfhydryl group of cysteine, amino groups of cytosine and guanine, and cyanide ions also react with ninhydrin to form various chromophores of analytical interest. Since its discovery, extensive efforts have been made to apply manual and automated ninhydrin reactions as well as ninhydrin spray reagents to the detection, isolation, and analysis of numerous compounds of interest across a broad spectrum of disciplines. These include agricultural, biochemical, clinical, environmental, food, forensic, histochemical, microbiological, medical, nutritional, plant, and protein sciences. This reaction is unique among chromogenic reactions in that at pH 5.5 it results in the formation of the same soluble chromophore by all primary amines which react, be they amines, amino acids, peptides, proteins, and even ammonia. Because the chromophore is not chemically bound to the protein or other insoluble material, it is not lost when the insoluble substrate is removed by centrifugation or filtration after the reaction is completed. The visible color of the chromophore is distinctive and is generally not affected by the yellow colors present in many food, plant, and tissue extracts. Adaptations of the classical ninhydrin reaction to specialized needs in analytical chemistry and biochemistry include the use of acid, alkaline, and fluorogenic ninhydrin reagents. To cross-fertilize information among several disciplines wherein an interest in the ninhydrin reaction has developed, and to enhance its utility, this review attempts to integrate and correlate the widely scattered literature on ninhydrin reactions of a variety of structurally different compounds. Specifically covered are the following aspects: historical perspective, chemistry and mechanisms, applications, and research needs. A better understanding of these multifaceted ninhydrin reactions provide a scientific basis for further improvements of this important analytical technique.