The genome sequence of Treponema pallidum, the syphilis spirochete: will clinicians benefit?

Novel Treponema pallidum Recombinant Antigens for Syphilis Diagnostics: Current Status and Future Prospects

The recombinant protein technology considerably promoted the development of rapid and accurate treponema-specific laboratory diagnostics of syphilis infection. For the last ten years, the immunodominant recombinant inner membrane lipoproteins are proved to be sensitive and specific antigens for syphilis screening. However, the development of an enlarged T. pallidum antigen panel for diagnostics of early and late syphilis and differentiation of syphilis stages or cured syphilis remains as actual goal of multidisciplinary expertise. Current review revealed novel recombinant antigens: surface-exposed proteins, adhesins, and periplasmic and flagellar proteins, which are promising candidates for the improved syphilis serological diagnostics. The opportunities and limitations of diagnostic usage of these antigens are discussed and the criteria for selection of optimal antigens panel summarized.

Modern clinical microbiology: new challenges and solutions

In the twenty-first century, the clinical microbiology laboratory plays a central part in optimizing the management of infectious diseases and surveying local and global epidemiology. This pivotal role is made possible by the adoption of rational sampling, point-of-care tests, extended automation and new technologies, including mass spectrometry for colony identification, real-time genomics for isolate characterization, and versatile and permissive culture systems. When balanced with cost, these developments can improve the workflow and output of clinical microbiology laboratories and, by identifying and characterizing microbial pathogens, provide significant input to scientific discovery.

Virulence factors of the oral spirochete Treponema denticola

There is compelling evidence that treponemes are involved in the etiology of several chronic diseases, including chronic periodontitis as well as other forms of periodontal disease. There are interesting parallels with other chronic diseases caused by treponemes that may indicate similar virulence characteristics. Chronic periodontitis is a polymicrobial disease, and recent animal studies indicate that co-infection of Treponema denticola with other periodontal pathogens can enhance alveolar bone resorption. The bacterium has a suite of molecular determinants that could enable it to cause tissue damage and subvert the host immune response. In addition to this, it has several non-classic virulence determinants that enable it to interact with other pathogenic bacteria and the host in ways that are likely to promote disease progression. Recent advances, especially in molecular-based methodologies, have greatly improved our knowledge of this bacterium and its role in disease.

Analysis of the IgG immune response to Treponema phagedenis-like spirochetes in individual dairy cattle with papillomatous digital dermatitis

Papillomatous digital dermatitis (PDD) is a major infectious disease of the foot skin in dairy cattle. Treponema phagedenis-like spirochetes have been consistently detected in PDD lesions, and antibodies against these organisms have been demonstrated in affected cattle. However, little is known about the dominant antigens recognized by the immune system of affected cattle. Here, we investigated the IgG immune response to T. phagedenis-like isolates by Western blotting with different sera using whole-cell lysates and extracted glycolipid from 18 and 8 isolates, respectively, including those from different cattle on the same or different farms, isolates from different lesions affecting a single cow, and different isolates from the same lesion affecting a single cow. The reactivity of sera in Western blot assays revealed different banding patterns or showed no bands, suggesting that considerable antigenic variations, including glycolipid, may exist among the isolates, even in those from single individuals. With use of a total of 151 serum samples collected from three groups of cattle, i.e., PDD-positive cows on PDD-positive farms (group A), PDD-negative cows on PDD-positive farms (group B), and cows on PDD-free farms (group C), the levels of IgG antibodies against four T. phagedenis-like isolates were measured by enzyme-linked immunosorbent assay (ELISA). The optical density in groups A and B was significantly higher than that in group C, even though the value varied among the antigens used. Therefore, combinations of multiple Treponema species should be used for serological analysis and the development of a suitable vaccine because of antigenic variations.

Congenital syphilis: a continuing but neglected problem

Congenital syphilis was rare in most affluent countries but there has been a slight resurgence recently in several European countries. In large parts of the world and particularly sub-Saharan Africa congenital syphilis is a significant public health problem. The cornerstone of congenital syphilis control is antenatal screening and treatment of mothers with penicillin, which is a cost-effective intervention. In affluent countries it should be strengthened among those at high risk. Clinicians should be more vigilant for the possibility of babies being born with congenital syphilis, which is often asymptomatic. In developing countries not only does antenatal care screening need to be strengthened by implementing point-of-care decentralised screening and treatment but alternative innovative approaches to controlling congenital syphilis should be explored. There is an urgent need for international health agencies to support focused approaches to tackling the tragedy of continuing congenital syphilis. This could be a part of a pro-poor strategy to meet the Millennium Development Goals.

Syphilis in Children: Congenital and Acquired

Syphilis rates in women and congenital syphilis rates have declined steadily in the United States in recent years. However, syphilis remains a worldwide public health problem, with more than 12 million cases in adults and more than half a million pregnancies affected yearly. Prenatal screening and treatment programs are limited or nonexistent in many developing countries. The genome of Treponema pallidum, one of the smallest among prokaryotes, has been sequenced, but methods for continuous in vitro cultivation of the microbe remain elusive. There are no promising candidates for future vaccines at this time. Serologic testing, for both specific treponemal and nontreponemal antibodies, continues to be a primary means of diagnosis. Penicillin remains the drug of choice for congenital and acquired syphilis in childhood. The diagnosis of syphilis beyond early infancy raises concerns for possible child sexual abuse, although progression of congenital syphilis may account for some cases. Syphilis is a potentially eradicable disease, but this can be achieved only with sustained international will and cooperation to fund the necessary screening and treatment programs.

The pathogenesis of syphilis: the Great Mimicker, revisited

Syphilis is a chronic sexually transmitted infection caused by Treponema pallidum subspecies pallidum. Its protean clinical presentations earned it the name of the 'Great Mimicker'. Understanding of disease pathogenesis and how host-pathogen interactions influence the course of disease have been compromised by the facts that the organism cannot be grown in vitro and, as an exclusively human pathogen, inferences made from animal models are of limited applicability. Many questions remain about how T. pallidum biology contributes to distinctive features of syphilis, such as its ability to persist in the presence of a brisk host response or its propensity for neuro-invasion and congenital transmission. In 1998, the genome of T. pallidum was sequenced. The organism has a relatively small genome, suggesting that it utilizes host biosynthesis to fulfil some of its metabolic needs. While biological functions are suggested for only about 55% of T. pallidum's 1041 open reading frames, even these relatively early studies offer important insights into syphilis pathogenesis. A family of repeat genes, the Tp genes, encode proteins homologous to the major sheath proteins of T. denticola. Antibodies to the TprK variable regions are protective in a rabbit model. With successive passage, increasing diversity is observed in the TprK V region genes. Antigenic variation through gene conversion has been hypothesized to be one mechanism of escaping immune surveillance, allowing for prolonged infection and persistence in the presence of a robust host response. Human and animal studies suggest that a Th1 response is elicited in primary syphilis. Progression to the secondary stage is accompanied by a shift to a Th2 response, allowing for incomplete clearance of the pathogen. In pregnancy, intense inflammatory responses and prostaglandins induced by fetal infection may be responsible for fetal death or pre-term delivery and severe growth retardation or other manifestations of congenital syphilis. Understanding of the molecular targets of these immune responses may facilitate the development of vaccines for syphilis.

Elaboration of enzyme immunoassay based on recombinant antigens and intended for diagnostics of syphilis

Enzyme immunoassay (EIA) using recombinant antigens for the detection of Treponema pallidum-specific antibodies in sera of syphilis patients was developed. Four low-molar-mass Treponema antigens (Tp15, Tp17, TmpA, Tp47) were investigated; 17- and 47-kDa proteins were demonstrated as immunodominant as they permitted to obtain the most sensitive EIA. Using a mixture of these proteins a 3rd-generation-EIA kit Dia-Syph was constructed, its sensitivity being 99.4% during tests of 165 sera of syphilitic patients. No false result was obtained on the commercial panel PSS01 (BBI, USA). The specificity of the elaborated test system (99.7%) was determined on 295 sera.

Reverse vaccinology

Biochemical, serological and microbiological methods have been used to dissect pathogens and identify the components useful for vaccine development. Although successful in many cases, this approach is time-consuming and fails when the pathogens cannot be cultivated in vitro, or when the most abundant antigens are variable in sequence. Now genomic approaches allow prediction of all antigens, independent of their abundance and immunogenicity during infection, without the need to grow the pathogen in vitro. This allows vaccine development using non-conventional antigens and exploiting non-conventional arms of the immune system. Many vaccines impossible to develop so far will become a reality. Since the process of vaccine discovery starts in silico using the genetic information rather than the pathogen itself, this novel process can be named reverse vaccinology.