Functional characterization of IScs605, an insertion element carried by tetracycline-resistant Chlamydia suis

Chlamydia suis displays high transformation capacity with complete cloning vector integration into the chromosomal rrn-nqrF plasticity zone

IMPORTANCE

The obligate intracellular Chlamydia genus contains many pathogens with a negative impact on global health and economy. Despite recent progress, there is still a lack of genetic tools limiting our understanding of these complex bacteria. This study provides new insights into genetic manipulation of Chlamydia with the opportunistic porcine pathogen Chlamydia suis, the only chlamydial species naturally harboring an antibiotic resistance gene, originally obtained by horizontal gene transfer. C. suis is transmissible to humans, posing a potential public health concern. We report that C. suis can take up vectors that lack the native plasmid, a requirement for most chlamydial transformation systems described to date. Additionally, we show that C. trachomatis, the most common cause for bacterial sexually transmitted infections and infectious blindness worldwide, can be transformed with C. suis vectors. Finally, the chromosomal region that harbors the resistance gene of C. suis is highly susceptible to complete vector integration.

Detection of Acquired Antibiotic Resistance Genes in Domestic Pig (Sus scrofa) and Common Carp (Cyprinus carpio) Intestinal Samples by Metagenomics Analyses in Hungary

The aim of this study was metagenomics analyses of acquired antibiotic-resistance genes (ARGs) in the intestinal microbiome of two important food-animal species in Hungary from a One Health perspective. Intestinal content samples were collected from 12 domestic pigs (Sus scrofa) and from a common carp (Cyprinus carpio). Shotgun metagenomic sequencing of DNA purified from the intestinal samples was performed on the Illumina platform. The ResFinder database was applied for detecting acquired ARGs in the assembled metagenomic contigs. Altogether, 59 acquired ARG types were identified, 51 genes from domestic pig and 12 genes from the carp intestinal microbiome. ARG types belonged to the antibiotic classes aminoglycosides (27.1%), tetracyclines (25.4%), β-lactams (16.9%), and others. Of the identified ARGs, tet(E), a bla_OXA-_48-like β-lactamase gene, as well as cphA4, ampS, aadA2, qnrS2, and sul1, were identified only in carp but not in swine samples. Several of the detected acquired ARGs have not yet been described from food animals in Hungary. The tet(Q), tet(W), tet(O), and mef(A) genes detected in the intestinal microbiome of domestic pigs had also been identified from free-living wild boars in Hungary, suggesting a possible relationship between the occurrence of acquired ARGs in domestic and wild animal populations.

The Impact of Lateral Gene Transfer in Chlamydia

Lateral gene transfer (LGT) facilitates many processes in bacterial ecology and pathogenesis, especially regarding pathogen evolution and the spread of antibiotic resistance across species. The obligate intracellular chlamydiae, which cause a range of diseases in humans and animals, were historically thought to be highly deficient in this process. However, research over the past few decades has demonstrated that this was not the case. The first reports of homologous recombination in the Chlamydiaceae family were published in the early 1990s. Later, the advent of whole-genome sequencing uncovered clear evidence for LGT in the evolution of the Chlamydiaceae, although the acquisition of tetracycline resistance in Chlamydia (C.) suis is the only recent instance of interphylum LGT. In contrast, genome and in vitro studies have shown that intraspecies DNA exchange occurs frequently and can even cross species barriers between closely related chlamydiae, such as between C. trachomatis, C. muridarum, and C. suis. Additionally, whole-genome analysis led to the identification of various DNA repair and recombination systems in C. trachomatis, but the exact machinery of DNA uptake and homologous recombination in the chlamydiae has yet to be fully elucidated. Here, we reviewed the current state of knowledge concerning LGT in Chlamydia by focusing on the effect of homologous recombination on the chlamydial genome, the recombination machinery, and its potential as a genetic tool for Chlamydia.

Generation of Tetracycline and Rifamycin Resistant Chlamydia Suis Recombinants

The Chlamydiaceae are a family of obligate intracellular, gram-negative bacteria known to readily exchange DNA by homologous recombination upon co-culture in vitro, allowing the transfer of antibiotic resistance residing on the chlamydial chromosome. Among all the obligate intracellular bacteria, only Chlamydia (C.) suis naturally integrated a tetracycline resistance gene into its chromosome. Therefore, in order to further investigate the readiness of Chlamydia to exchange DNA and especially antibiotic resistance, C. suis is an excellent model to advance existing co-culture protocols allowing the identification of factors crucial to promote homologous recombination in vitro. With this strategy, we co-cultured tetracycline-resistant with rifamycin group-resistant C. suis, which resulted in an allover recombination efficiency of 28%. We found that simultaneous selection is crucial to increase the number of recombinants, that sub-inhibitory concentrations of tetracycline inhibit rather than promote the selection of double-resistant recombinants, and identified a recombination-deficient C. suis field isolate, strain SWA-110 (1-28b). While tetracycline resistance was detected in field isolates, rifampicin/rifamycin resistance (RifR) had to be induced in vitro. Here, we describe the protocol with which RifR C. suis strains were generated and confirmed. Subsequent whole-genome sequencing then revealed that G530E and D461A mutations in rpoB, a gene encoding for the β-subunit of the bacterial RNA polymerase (RNAP), was likely responsible for rifampicin and rifamycin resistance, respectively. Finally, whole-genome sequencing of recombinants obtained by co-culture revealed that recombinants picked from the same plate may be sibling clones and confirmed C. suis genome plasticity by revealing variable, apparently non-specific areas of recombination.

Chlamydia Lipooligosaccharide Has Varied Direct and Indirect Roles in Evading both Innate and Adaptive Host Immune Responses

Chlamydia bacteria are obligate intracellular pathogens which can cause a variety of disease in humans and other vertebrate animals. To successfully complete its life cycle, Chlamydia must evade both intracellular innate immune responses and adaptive cytotoxic T cell responses. Here, we report on the role of the chlamydial lipooligosaccharide (LOS) in evading the immune response. Chlamydia infection is known to block the induction of apoptosis. However, when LOS synthesis was inhibited during Chlamydia trachomatis infection, HeLa cells regained susceptibility to apoptosis induction following staurosporine treatment. Additionally, the delivery of purified LOS to the cytosol of cells increased the levels of the antiapoptotic protein survivin. An increase in survivin levels was also detected following C. trachomatis infection, which was reversed by blocking LOS synthesis. Interestingly, while intracellular delivery of lipopolysaccharide (LPS) derived from Escherichia coli was toxic to cells, LOS from C. trachomatis did not induce any appreciable cell death, suggesting that it does not activate pyroptosis. Chlamydial LOS was also a poor stimulator of maturation of bone marrow-derived dendritic cells compared to E. coli LPS. Previous work from our group indicated that LOS synthesis during infection was necessary to alter host cell antigen presentation. However, direct delivery of LOS to cells in the absence of infection did not alter antigenic peptide presentation. Taken together, these data suggest that chlamydial LOS, which is remarkably conserved across the genus Chlamydia, may act both directly and indirectly to allow the pathogen to evade the innate and adaptive immune responses of the host.

Comprehensive genome analysis and comparisons of the swine pathogen, Chlamydia suis reveals unique ORFs and candidate host-specificity factors

Chlamydia suis, a ubiquitous swine pathogen, has the potential for zoonotic transmission to humans and often encodes for resistance to the primary treatment antibiotic, tetracycline. Because of this emerging threat, comparative genomics for swine isolate R19 with inter- and intra-species genomes was performed. A 1.094 Mb genome was determined through de novo assembly of Illumina high throughput sequencing reads. Annotation and subsystem analyses were conducted, revealing 986 putative genes (Chls_###) that are predominantly orthologs to other known Chlamydia genes. Subsequent comparative genomics revealed a high level of genomic synteny and overall sequence identity with other Chlamydia while 92 unique C. suis open reading frames were annotated. Direct comparison of Chlamydia-specific gene families that included the plasticity zone, inclusion membrane proteins, polymorphic membrane proteins and the major outer membrane protein, demonstrated high gene content identity with C. trachomatis and C. muridarum. These comparisons also identified diverse components that potentially could contribute to host-specificity. This study constitutes the first genome-wide comparative analysis for C. suis, generating a fully annotated reference genome. These studies will enable focused efforts on factors that provide key species specificity and adaptation to cognate hosts that are attributed to chlamydial infections, including humans.

Diversity in Chlamydial plasmids

Background

Evolutionary studies have been conducted that have investigated the chromosomal variance in the genus of Chlamydia. However, no all-encompassing genus-wide comparison has been performed on the plasmid. Therefore, there is a gap in the current knowledge on Chlamydia plasmid diversity.

Aims

This project is aimed to investigate and establish the nature and extent of diversity across the entire genus of Chlamydia, by comparing the sequences of all currently available plasmid carrying strains.

Methods

The PUBMED database was used to identify plasmid sequences from all available strains that met the set quality criteria for their inclusion in the study. Alignments were performed on the 51 strains that fulfilled the criteria using MEGA X software. Following that Maximum Likelihood estimation was used to construct 11 phylogenetic trees of the whole plasmid sequence, the individual 8 coding sequences, the iteron and a chromosomal gene ompA as a comparator.

Results

The genus-wide plasmid phylogeny produced three distinct lineages labelled as alpha, beta and gamma. Nineteen genotypes were found in the initial whole plasmid analysis. Their distribution was allocated as six C. pecorum, two C. pneumoniae, one C. gallinacea, one C. avium, one C. caviae, one C. felis, two C. psittaci, one C. trachomatis, one C. muridarum, and two C. suis. The chromosomal comparative gene ompA supported this distribution, with the same number of primary clades with the same species distribution. However, ompA sequence comparison resulted in fewer genotypes due to a reduced amount of available sequences (33 out of 51). All results were statistically significant.

Conclusion

The results of this study indicate that the common bacterial ancestor of all the species had a plasmid, which has diverged over time. Moreover, it suggests that there is a strong evolutionary selection towards these species retaining their plasmids due to its high level of conservation across the genus, with the notable exception of C. pneumoniae. Furthermore, the evolutionary analysis showed that the plasmid and the chromosome have co-evolved.

New insights into chlamydial zoonoses

Chlamydiae are obligate intracellular bacterial pathogens of humans. Infections in animals are also widespread with some species, such as Chlamydia psittaci, long recognised as a serious threat to human health. Critical to the public health response of any zoonotic disease outbreaks is reliable and up-to-date information on the epidemiology of the target pathogen. Aided by advances in the use of quantitative PCR, molecular typing and culture-independent genomic studies, significant recent work has highlighted an expanded diversity and host range of chlamydial pathogens in animals. New and unexpected cases of chlamydial zoonoses have now been recently documented in Australia and elsewhere, emphasising the importance of multi-disciplinary ‘One Health' collaboration and the use of standardised methods to detect and characterise chlamydial pathogens in humans and animals.

One Aeromonas salmonicida subsp. salmonicida isolate with a pAsa5 variant bearing antibiotic resistance and a pRAS3 variant making a link with a swine pathogen

The Gram-negative bacterium Aeromonas salmonicida subsp. salmonicida is an aquatic pathogen which causes furunculosis to salmonids, especially in fish farms. The emergence of strains of this bacterium exhibiting antibiotic resistance is increasing, limiting the effectiveness of antibiotherapy as a treatment against this worldwide disease. In the present study, we discovered an isolate of A. salmonicida subsp. salmonicida that harbors two novel plasmids variants carrying antibiotic resistance genes. The use of long-read sequencing (PacBio) allowed us to fully characterize those variants, named pAsa5-3432 and pRAS3-3432, which both differ from their classic counterpart through their content in mobile genetic elements. The plasmid pAsa5-3432 carries a new multidrug region composed of multiple mobile genetic elements, including a Class 1 integron similar to an integrated element of Salmonella enterica. With this new region, probably acquired through plasmid recombination, pAsa5-3432 is the first reported plasmid of this bacterium that bears both an essential virulence factor (the type three secretion system) and multiple antibiotic resistance genes. As for pRAS3-3432, compared to the classic pRAS3, it carries a new mobile element that has only been identified in Chlamydia suis. Hence, with the identification of those two novel plasmids harboring mobile genetic elements that are normally encountered in other bacterial species, the present study puts emphasis on the important impact of mobile genetic elements in the genomic plasticity of A. salmonicida subsp. salmonicida and suggests that this aquatic bacterium could be an important reservoir of antibiotic resistance genes that can be exchanged with other bacteria, including human and animal pathogens.

Antimicrobial Resistance in Chlamydiales, Rickettsia, Coxiella, and Other Intracellular Pathogens

This article will provide current insights into antimicrobial susceptibilities and resistance of an important group of bacterial pathogens that are not phylogenetically related but share lifestyle similarities in that they are generally considered to be obligate intracellular microbes. As such, there are shared challenges regarding methods for their detection and subsequent clinical management. Similarly, from the laboratory perspective, susceptibility testing is rarely undertaken, though molecular approaches might provide new insights. One should also bear in mind that the highly specialized microbial lifestyle restricts the opportunity for lateral gene transfer and, consequently, acquisition of resistance.

The Chlamydia suis Genome Exhibits High Levels of Diversity, Plasticity, and Mobile Antibiotic Resistance: Comparative Genomics of a Recent Livestock Cohort Shows Influence of Treatment Regimes

Chlamydia suis is an endemic pig pathogen, belonging to a fascinating genus of obligate intracellular pathogens. Of particular interest, this is the only chlamydial species to have naturally acquired genes encoding for tetracycline resistance. To date, the distribution and mobility of the Tet-island are not well understood. Our study focused on whole genome sequencing of 29 C. suis isolates from a recent porcine cohort within Switzerland, combined with data from USA tetracycline-resistant isolates. Our findings show that the genome of C. suis is very plastic, with unprecedented diversity, highly affected by recombination and plasmid exchange. A large diversity of isolates circulates within Europe, even within individual Swiss farms, suggesting that C. suis originated around Europe. New World isolates have more restricted diversity and appear to derive from European isolates, indicating that historical strain transfers to the United States have occurred. The architecture of the Tet-island is variable, but the tetA(C) gene is always intact, and recombination has been a major factor in its transmission within C. suis. Selective pressure from tetracycline use within pigs leads to a higher number of Tet-island carrying isolates, which appear to be lost in the absence of such pressure, whereas the loss or gain of the Tet-island from individual strains is not observed. The Tet-island appears to be a recent import into the genome of C. suis, with a possible American origin.

Tet(C) Gene Transfer between Chlamydia suis Strains Occurs by Homologous Recombination after Co-infection: Implications for Spread of Tetracycline-Resistance among Chlamydiaceae

Chlamydia suis is a swine pathogen that has also recently been found to cause zoonotic infections of the human eye, pharynx, and gastrointestinal tract. Many strains contain a tetracycline class C gene [tet(C)] cassette that confers tetracycline resistance. The cassette was likely originally acquired by horizontal gene transfer from a Gram-negative donor after the introduction of tetracycline into animal feed in the 1950s. Various research groups have described the capacity for different Chlamydia species to exchange DNA by homologous recombination. Since over 90% of C. suis strains are tetracycline resistant, they represent a potential source for antibiotic-resistance spread within and between Chlamydiaceae species. Here, we examined the genetics of tet(C)-transfer among C. suis strains. Tetracycline-sensitive C. suis strain S45 was simultaneously or sequentially co-infected with tetracycline-resistant C. suis strains in McCoy cells. Potential recombinants were clonally purified by a harvest assay derived from the classic plaque assay. C. suis strain Rogers132, lacking transposases IS200 and IS605, was the most efficient donor, producing two unique recombinants detected in three of the 56 (5.4%) clones screened. Recombinants were found to have a minimal inhibitory concentration (MIC) of 8-16 μg/mL for tetracycline. Resistance remained stable over 10 passages as long as recombinants were initially grown in tetracycline at twice the MIC of S45 (0.032 μg/mL). Genomic analysis revealed that tet(C) had integrated into the S45 genome by homologous recombination at two unique sites depending on the recombinant: a 55 kb exchange between nrqF and pckG, and a 175 kb exchange between kdsA and cysQ. Neither site was associated with inverted repeats or motifs associated with recombination hotspots. Our findings show that cassette transfer into S45 has low frequency, does not require IS200/IS605 transposases, is stable if initially grown in tetracycline, and results in multiple genomic configurations. We provide a model for stable cassette transfer to better understand the capability for cassette acquisition by Chlamydiaceae species that infect humans, a matter of public health importance.

Emancipating Chlamydia: Advances in the Genetic Manipulation of a Recalcitrant Intracellular Pathogen

Chlamydia species infect millions of individuals worldwide and are important etiological agents of sexually transmitted disease, infertility, and blinding trachoma. Historically, the genetic intractability of this intracellular pathogen has hindered the molecular dissection of virulence factors contributing to its pathogenesis. The obligate intracellular life cycle of Chlamydia and restrictions on the use of antibiotics as selectable markers have impeded the development of molecular tools to genetically manipulate these pathogens. However, recent developments in the field have resulted in significant gains in our ability to alter the genome of Chlamydia, which will expedite the elucidation of virulence mechanisms. In this review, we discuss the challenges affecting the development of molecular genetic tools for Chlamydia and the work that laid the foundation for recent advancements in the genetic analysis of this recalcitrant pathogen.

Chlamydial Antibiotic Resistance and Treatment Failure in Veterinary and Human Medicine

The Chlamydiaceae are widespread pathogens of both humans and animals. Chlamydia trachomatis infection causes blinding trachoma and reproductive complications in humans. Chlamydia pneumoniae causes human respiratory tract infections and atypical pneumonia. Chlamydia suis infection is associated with conjunctivitis, diarrhea, and failure to gain weight in domestic swine. Chlamydial infections in humans and domesticated animals are generally controlled by antibiotic treatment—particularly macrolides (usually azithromycin) and tetracyclines (tetracycline and doxycycline). Tetracycline-containing feed has also been used to limit infections and promote growth in livestock populations, although its use has decreased because of growing concerns about antimicrobial resistance development. Because Sandoz and Rockey published an elegant review of chlamydial anti-microbial resistance in 2010, we will review the following: (i) antibiotic resistance in C. suis, (ii) recent evidence for acquired resistance in human chlamydial infections, and (iii) recent non-genetic mechanisms of antibiotic resistance that may contribute to treatment failure.

Amoebal endosymbiont Neochlamydia genome sequence illuminates the bacterial role in the defense of the host amoebae against Legionella pneumophila

Previous work has shown that the obligate intracellular amoebal endosymbiont Neochlamydia S13, an environmental chlamydia strain, has an amoebal infection rate of 100%, but does not cause amoebal lysis and lacks transferability to other host amoebae. The underlying mechanism for these observations remains unknown. In this study, we found that the host amoeba could completely evade Legionella infection. The draft genome sequence of Neochlamydia S13 revealed several defects in essential metabolic pathways, as well as unique molecules with leucine-rich repeats (LRRs) and ankyrin domains, responsible for protein-protein interaction. Neochlamydia S13 lacked an intact tricarboxylic acid cycle and had an incomplete respiratory chain. ADP/ATP translocases, ATP-binding cassette transporters, and secretion systems (types II and III) were well conserved, but no type IV secretion system was found. The number of outer membrane proteins (OmcB, PomS, 76-kDa protein, and OmpW) was limited. Interestingly, genes predicting unique proteins with LRRs (30 genes) or ankyrin domains (one gene) were identified. Furthermore, 33 transposases were found, possibly explaining the drastic genome modification. Taken together, the genomic features of Neochlamydia S13 explain the intimate interaction with the host amoeba to compensate for bacterial metabolic defects, and illuminate the role of the endosymbiont in the defense of the host amoebae against Legionella infection.

Expression and targeting of secreted proteins from Chlamydia trachomatis

Chlamydia trachomatis is an obligate intracellular pathogen that replicates in a vacuole termed the inclusion. Many of the interactions of chlamydiae with the host cell are dependent upon bacterial protein synthesis and presumably exposure of these proteins to the cytosol. Because of the dearth of genetic tools for chlamydiae, previous studies examining secreted proteins required the use of heterologous bacterial systems. Recent advances in genetic manipulation of chlamydia now allow for transformation of the bacteria with plasmids. We describe here a shuttle vector system, pBOMB4, that permits expression of recombinant proteins under constitutive or conditional promoter control. We show that the inclusion membrane protein IncD is secreted in a type III-dependent manner from Yersinia pseudotuberculosis and also secreted from C. trachomatis in infected cells where it localizes appropriately to the inclusion membrane. IncD truncated of the first 30 amino acids containing the secretion signal is no longer secreted and is retained by the bacteria. Cytosolic exposure of secreted proteins can be confirmed by using CyaA, GSK, or microinjection assays. A protein predicted to be retained within the bacteria, NrdB is indeed localized to the chlamydia. In addition, we have shown that the chlamydial effector protein, CPAF, which is secreted into the host cell cytosol by a Sec-dependent pathway, also accesses the cytosol when expressed from this system. These assays should prove useful to assess the secretion of other chlamydial proteins that are potentially exposed to the cytosol of the host cell.

Chlamydial biology and its associated virulence blockers

Chlamydiales are obligate intracellular parasites of eukaryotic cells. They can be distinguished from other Gram-negative bacteria through their characteristic developmental cycle, in addition to special biochemical and physical adaptations to subvert the eukaryotic host cell. The host spectrum includes humans and other mammals, fish, birds, reptiles, insects and even amoeba, causing a plethora of diseases. The first part of this review focuses on the specific chlamydial infection biology and metabolism. As resistance to classical antibiotics is emerging among Chlamydiae as well, the second part elaborates on specific compounds and tools to block chlamydial virulence traits, such as adhesion and internalization, Type III secretion and modulation of gene expression.

Results of total DNA measurement in koi tissue by Koi Herpes Virus real-time PCR

Koi Herpes Virus (KHV) has been classified recently as a member of the Alloherpesviridae within the Herpesvirales order (Waltzek et al., 2005). Although one of the unique features of Herpesviridae, the sister family of Herpesvirales, is latent infection, it has not been demonstrated consistently that KHV of Alloherpesviridae can cause latent infection and be reactivated from latency. To investigate if KHV genomic DNA is present in koi exposed to KHV infection, 10 healthy fish were investigated from a koi population with a history of a KHV outbreak. No gross lesions or microscopic changes were observed at necropsy or by histological examination. No infectious virus was isolated from either the blood plasma or tissues. However, KHV DNA was detected in the white blood cells of nine of the ten fish by real-time PCR and PCR-Southern blot. KHV DNA was also detected in the brain, eye, spleen, gills hematopoietic kidney, trunk kidney, and intestine of nine of the ten fish by PCR-Southern blot. Interestingly, KHV DNA was also detected in the intestinal contents from seven of ten koi. Portions of major capsid gene DNA, amplified from two of the ten koi WBCs, were found to be identical to KHV-U. This study demonstrated that KHV genomic DNA can be detected in normal koi exposed previously to KHV and suggests that KHV becomes latent in fish.

Chlamydiaceae in cattle: commensals, trigger organisms, or pathogens?

Epidemiological data indicate that infection of cattle with chlamydiae such as Chlamydophila (C.) pecorum, C. abortus, C. psittaci and Chlamydia suis, is ubiquitous with mixed infections occurring frequently. The apparent lack of association between infection and clinical disease has resulted in debate as to the pathogenic significance of these organisms, and their tendency to sub-clinical and/or persistent infection presents a challenge to the study of their potential effects. However, recent evidence indicates that chlamydial infections have a substantial and quantifiable impact on livestock productivity with chronic, recurrent infections associated with pulmonary disease in calves and with infertility and sub-clinical mastitis in dairy cows. Data also suggest these infections manifest clinically when they coincide with a number of epidemiological risk factors. Future research should: (1) use relevant animal models to clarify the pathogenesis of bovine chlamydioses; (2) quantify the impact of chlamydial infection at a herd level and identify strategies for its control, including sub-unit vaccine development; and (3) evaluate the zoonotic risk of bovine chlamydial infections which will require the development of species-specific serodiagnostics.

Antibiotic resistance in Chlamydiae

There are few documented reports of antibiotic resistance in Chlamydia and no examples of natural and stable antibiotic resistance in strains collected from humans. While there are several reports of clinical isolates exhibiting resistance to antibiotics, these strains either lost their resistance phenotype in vitro, or lost viability altogether. Differences in procedures for chlamydial culture in the laboratory, low recovery rates of clinical isolates and the unknown significance of heterotypic resistance observed in culture may interfere with the recognition and interpretation of antibiotic resistance. Although antibiotic resistance has not emerged in chlamydiae pathogenic to humans, several lines of evidence suggest they are capable of expressing significant resistant phenotypes. The adept ability of chlamydiae to evolve to antibiotic resistance in vitro is demonstrated by contemporary examples of mutagenesis, recombination and genetic transformation. The isolation of tetracycline-resistant Chlamydia suis strains from pigs also emphasizes their adaptive ability to acquire antibiotic resistance genes when exposed to significant selective pressure.

Recurrence of Chlamydiasuis infection in pigs after short-term antimicrobial treatment

The effect of short-term antimicrobial treatment on natural excretion of Chlamydia suis in rectal swabs and C. suis and Chlamydophila psittaci in nasal swabs was investigated in 47 clinically normal piglets by quantitative real-time PCR. Pigs were treated IM with 4 mg/kg enrofloxacin for 5 days (n = 22) or 2.5mg/kg enrofloxacin for 3 days followed by 100mg/mL tiamulin (n = 25). Antimicrobial treatment reduced the number of pigs positive for chlamydiae and the quantity of chlamydial DNA in positive swabs for a few days, but chlamydial excretion recurred in both groups. Short-term antimicrobial treatment at dosages recommended for treatment of other bacterial infections in pig herds was not effective in eliminating naturally occurring subclinical chlamydial infection in pigs.

A novel inhibitor of Chlamydophila pneumoniae protein kinase D (PknD) inhibits phosphorylation of CdsD and suppresses bacterial replication

Background

We have shown previously that Chlamydophila pneumoniae contains a dual-specific Ser/Thr protein kinase that phosphorylates CdsD, a structural component of the type III secretion apparatus. To further study the role of PknD in growth and development we sought to identify a PknD inhibitor to determine whether PknD activity is required for replication.

Results

Using an in vitro kinase assay we screened 80 known eukaryotic protein kinase inhibitors for activity against PknD and identified a 3'-pyridyl oxindole compound that inhibited PknD autophosphorylation and phosphorylation of CdsD. The PknD inhibitor significantly retarded the growth rate of C. pneumoniae as evidenced by the presence of very small inclusions with a reduced number of bacteria as seen by electron microscopy. These inclusions contained the normal replicative forms including elementary bodies (EB), intermediate bodies (IB) and reticulate bodies (RB), but lacked persistent bodies (PB), indicating that induction of persistence was not the cause of reduced chlamydial growth. Blind passage of C. pneumoniae grown in the presence of this PknD inhibitor for 72 or 84 hr failed to produce inclusions, suggesting this compound blocks an essential step in the production of infectious chlamydial EB. The compound was not toxic to HeLa cells, did not block activation of the MEK/ERK pathway required for chlamydial invasion and did not block intracellular replication of either Chlamydia trachomatis serovar D or Salmonella enterica sv. Typhimurium suggesting that the inhibitory effect of the compound is specific for C. pneumoniae.

Conclusion

We have identified a 3'-pyridyl oxindole compound that inhibits the in vitro kinase activity of C. pneumoniae PknD and inhibits the growth and production of infectious C. pneumoniae progeny in HeLa cells. Together, these results suggest that PknD may play a key role in the developmental cycle of C. pneumoniae.

Horizontal transfer of tetracycline resistance among Chlamydia spp. in vitro

There are no examples of stable tetracycline resistance in clinical strains of Chlamydia trachomatis. However, the swine pathogen Chlamydia suis is commonly tetracycline resistant, both in America and in Europe. In tested U.S. strains, this resistance is mediated by a genomic island carrying a tet(C) allele. In the present study, the ability of C. suis to mobilize tet(C) into other chlamydial species was examined. Differently antibiotic resistant strains of C. suis, C. trachomatis, and Chlamydia muridarum were used in coculture experiments to select for multiply antibiotic resistant progeny. Coinfection of mammalian cells with a naturally occurring tetracycline-resistant strain of C. suis and a C. muridarum or C. trachomatis strain containing selected mutations encoding rifampin (rifampicin) or ofloxacin resistance readily produced doubly resistant recombinant clones that demonstrated the acquisition of tetracycline resistance. The resistance phenotype in the progeny from a C. trachomatis L2/ofl(R)-C. suis R19/tet(R) cross resulted from integration of a 40-kb fragment into a single ribosomal operon of a recipient, leading to a merodiploid structure containing three rRNA operons. In contrast, a cross between C. suis R19/tet(R) and C. muridarum MoPn/ofl(R) led to a classical double-crossover event transferring 99 kb of DNA from C. suis R19/tet(R) into C. muridarum MoPn/ofl(R). Tetracycline resistance was also transferred to recent clinical strains of C. trachomatis. Successful crosses were not obtained when a rifampin-resistant Chlamydophila caviae strain was used as a recipient for crosses with C. suis or C. trachomatis. These findings provide a platform for further exploration of the biology of horizontal gene transfer in Chlamydia while bringing to light potential public health concerns generated by the possibility of acquisition of tetracycline resistance by human chlamydial pathogens.

Zoonotic Chlamydophila psittaci infections from a clinical perspective

Human psittacosis is a zoonotic infectious disease which is caused by the obligate intracellular bacterium Chlamydophila psittaci. Transmission of the disease usually originates from close contact with infected birds, most frequently in the context of the poultry industry, and from contact with Psittaciformes (cockatoos, parrots, parakeets and lories). Due to a low awareness of the disease and a variable clinical presentation psittacosis is often not recognised as such by general practitioners. This review therefore gives an overview of the epidemiology, symptoms, diagnosis and possible treatments for psittacosis in humans. The current case definition for epidemiological surveillance, as issued by the CDC, is discussed, as well as the possible emergence of Cp. psittaci antibiotic-resistant strains. There is an urgent need for information and for awareness campaigns directed at professional health care workers and the general public. In addition, a broader use of new diagnostic methods in medical laboratories and the development of prophylactics are called for.

Chlamydophila psittaci transmission from pet birds to humans

We studied zoonotic transmission of Chlamydophila psittaci in 39 breeding facilities for Psittaciformes (cockatoos, parrots, parakeets, lories) that frequently used antimicrobial drugs. Genotypes A or E/B were detected in 14.9% of humans at these facilities. Information on antimicrobial drug use in Psittaciformes and a C. psittaci vaccine are urgently required.

Chlamydophila psittaci genotype E/B transmission from African grey parrots to humans

Thirty-six birds from a parrot relief and breeding centre, as well as the manager, were examined for the presence of Chlamydophila psittaci. In the relief unit, 5 of 20 African grey parrots showed depression, ruffled feathers, loss of weight and mild dyspnoea. The birds received no antibiotic treatment. Birds of the breeding unit, 14 blue and gold macaws and 2 green-winged macaws, were healthy. They received doxycycline at the start of each breeding season. The manager complained of shortness of breath but took no medication. Using a nested PCR enzyme immunoassay (EIA), Cp. psittaci was detected in the faeces of all five sick birds, as well as in a nasal and pharyngeal swab from the manager. The veterinarian and her assistant became infected while sampling the parrots, as pharyngeal and nasal swabs from both were positive by nested PCR/EIA after visiting the parrot relief and breeding centre, but they showed no clinical signs of infection. Bacteria could be isolated from three of five nested PCR/EIA-positive birds, the manager and the veterinarian, but not from the veterinary assistant. Using an ompA genotype-specific real-time PCR, Cp. psittaci genotype E/B was identified as the transmitted strain. All breeding birds tested negative for Cp. psittaci. This is believed to be the first report on Cp. psittaci genotype E/B transmission from parrots to humans. In contradiction to genotype A strains, which are thought to be highly virulent to both birds and men, the currently described genotype E/B strain apparently caused no severe clinical symptoms in either parrots or humans.