The chlamydia: molecular biology of procaryotic obligate parasites of eucaryocytes

Association of environmental risk factors and trachoma in Gashoho Health District, Burundi

Background

Burundi is currently not meeting targets for elimination of trachoma and trichiasis by 2020 (GET2020). The recommended SAFE strategy (Surgery, antibiotics, face washing and environmental improvement) is currently not fully implemented in many areas of Burundi. The existence of associations between face-washing, sanitation and trachoma prevalence remain undocumented.

Methods

A convenience sample of 468 individuals from 117 households was drawn from attendees at trachoma clinics set up in four villages. Trachoma status, sex and age were recorded for all household members. Adult household members were surveyed about access to clean water and toilets, and knowledge of trachoma risk factors. Associations between cases of active trachoma per household and environmental risk factors were evaluated using generalised estimating equations.

Results

The overall prevalence of active trachoma was 7.1% (95% CI 5.0–9.6%), but 19.5% (95% CI13.7–26.4%) in children under nine years old. 0.9% (95% CI 0.3–2.0) of participants had trichiasis. Access to a sanitary toilet more than halved the odds of active trachoma (OR 0.43, 95% CI 0.25–0.74%), however, participants did not appreciate this association.

Conclusion

Access to sanitation was associated with the occurrence of active trachoma. Future research should focus on whether improving knowledge of and access to sanitation might reduce trachoma prevalence.

Chlamydia trachomatis Scavenges Host Fatty Acids for Phospholipid Synthesis via an Acyl-Acyl Carrier Protein Synthetase

The obligate intracellular parasite Chlamydia trachomatis has a reduced genome but relies on de novo fatty acid and phospholipid biosynthesis to produce its membrane phospholipids. Lipidomic analyses showed that 8% of the phospholipid molecular species synthesized by C. trachomatis contained oleic acid, an abundant host fatty acid that cannot be made by the bacterium. Mass tracing experiments showed that isotopically labeled palmitic, myristic, and lauric acids added to the medium were incorporated into C. trachomatis-derived phospholipid molecular species. HeLa cells did not elongate lauric acid, but infected HeLa cell cultures elongated laurate to myristate and palmitate. The elongated fatty acids were incorporated exclusively into C. trachomatis-produced phospholipid molecular species. C. trachomatis has adjacent genes encoding the separate domains of the bifunctional acyl-acyl carrier protein (ACP) synthetase/2-acylglycerolphosphoethanolamine acyltransferase gene (aas) of Escherichia coli. The CT775 gene encodes an acyltransferase (LpaT) that selectively transfers fatty acids from acyl-ACP to the 1-position of 2-acyl-glycerophospholipids. The CT776 gene encodes an acyl-ACP synthetase (AasC) with a substrate preference for palmitic compared with oleic acid in vitro. Exogenous fatty acids were elongated and incorporated into phospholipids by Escherichia coli-expressing AasC, illustrating its function as an acyl-ACP synthetase in vivo. These data point to an AasC-dependent pathway in C. trachomatis that selectively scavenges host saturated fatty acids to be used for the de novo synthesis of its membrane constituents.

Chlamydia trachomatis Relies on Autonomous Phospholipid Synthesis for Membrane Biogenesis

The obligate intracellular parasite Chlamydia trachomatis has a reduced genome and is thought to rely on its mammalian host cell for nutrients. Although several lines of evidence suggest C. trachomatis utilizes host phospholipids, the bacterium encodes all the genes necessary for fatty acid and phospholipid synthesis found in free living Gram-negative bacteria. Bacterially derived phospholipids significantly increased in infected HeLa cell cultures. These new phospholipids had a distinct molecular species composition consisting of saturated and branched-chain fatty acids. Biochemical analysis established the role of C. trachomatis-encoded acyltransferases in producing the new disaturated molecular species. There was no evidence for the remodeling of host phospholipids and no change in the size or molecular species composition of the phosphatidylcholine pool in infected HeLa cells. Host sphingomyelin was associated with C. trachomatis isolated by detergent extraction, but it may represent contamination with detergent-insoluble host lipids rather than being an integral bacterial membrane component. C. trachomatis assembles its membrane systems from the unique phospholipid molecular species produced by its own fatty acid and phospholipid biosynthetic machinery utilizing glucose, isoleucine, and serine.

How bacterial pathogens eat host lipids: implications for the development of fatty acid synthesis therapeutics

Bacterial type II fatty acid synthesis (FASII) is a target for the development of novel therapeutics. Bacteria incorporate extracellular fatty acids into membrane lipids, raising the question of whether pathogens use host fatty acids to bypass FASII and defeat FASII therapeutics. Some pathogens suppress FASII when exogenous fatty acids are present to bypass FASII therapeutics. FASII inhibition cannot be bypassed in many bacteria because essential fatty acids cannot be obtained from the host. FASII antibiotics may not be effective against all bacteria, but a broad spectrum of Gram-negative and -positive pathogens can be effectively treated with FASII inhibitors.

Type II fatty acid synthesis is essential for the replication of Chlamydia trachomatis

The major phospholipid classes of the obligate intracellular bacterial parasite Chlamydia trachomatis are the same as its eukaryotic host except that they also contain chlamydia-made branched-chain fatty acids in the 2-position. Genomic analysis predicts that C. trachomatis is capable of type II fatty acid synthesis (FASII). AFN-1252 was deployed as a chemical tool to specifically inhibit the enoyl-acyl carrier protein reductase (FabI) of C. trachomatis to determine whether chlamydial FASII is essential for replication within the host. The C. trachomatis FabI (CtFabI) is a homotetramer and exhibited typical FabI kinetics, and its expression complemented an Escherichia coli fabI(Ts) strain. AFN-1252 inhibited CtFabI by binding to the FabI·NADH complex with an IC50 of 0.9 μM at saturating substrate concentration. The x-ray crystal structure of the CtFabI·NADH·AFN-1252 ternary complex revealed the specific interactions between the drug, protein, and cofactor within the substrate binding site. AFN-1252 treatment of C. trachomatis-infected HeLa cells at any point in the infectious cycle caused a decrease in infectious titers that correlated with a decrease in branched-chain fatty acid biosynthesis. AFN-1252 treatment at the time of infection prevented the first cell division of C. trachomatis, although the cell morphology suggested differentiation into a metabolically active reticulate body. These results demonstrate that FASII activity is essential for C. trachomatis proliferation within its eukaryotic host and validate CtFabI as a therapeutic target against C. trachomatis.

Chlamydophila felis infection. ABCD guidelines on prevention and management

OVERVIEW

Chlamydophila felis is a Gram-negative bacterium and its primary target is the conjunctiva. The bacterium does not survive outside the host.

INFECTION

Transmission requires close contact between cats; ocular secretions are probably the most important body fluid for infection. Most cases occur in cats under 1 year of age. Chlamydophila felis is the infectious organism most frequently associated with conjunctivitis.

DISEASE SIGNS

Unilateral ocular disease generally progresses to become bilateral. There can be intense conjunctivitis with extreme hyperaemia of the nictitating membrane, blepharospasm and ocular discomfort. Transient fever, inappetence and weight loss may occur shortly after infection, although most cats remain well and continue to eat.

DIAGNOSIS

PCR techniques are now preferred for diagnosing C felis infection. Ocular swabs are generally used. In unvaccinated cats, antibody detection can be used to indicate infection.

DISEASE MANAGEMENT

Tetracyclines are generally regarded as the antibiotics of choice. Doxycycline has the advantage of requiring only single daily administration and is given at a dose of 10 mg/kg orally. Vaccination should be considered if there is a history of confirmed chlamydial disease in a shelter. Single housing and routine hygiene measures should suffice to avoid cross-infection. Cats maintained together for longer terms should be vaccinated regularly. In breeding catteries where C felis infection is endemic, the first step should be to treat all cats with doxycycline for at least 4 weeks. Once clinical signs have been controlled, the cats should be vaccinated.

VACCINATION RECOMMENDATIONS

Vaccination should be considered for cats at risk of exposure to infection. Vaccination generally begins at 8-10 weeks of age, with a second injection 3-4 weeks later. Annual boosters are recommended for cats at continued risk of exposure.

Enhancement of ATP levels and glucose metabolism during an infection by Chlamydia. NMR studies of living cells

The Chlamydia species are obligate intracellular bacteria that proliferate only within the infected cell. Since the extracellular bacteria are metabolically inert and there are no cell-free systems for characterizing Chlamydia metabolism, we studied metabolic changes related to ATP synthesis and glycolysis in HeLa cells infected with Chlamydia psittaci during the course of the 2-day infection cycle using noninvasive 31P and 13C NMR methods. We find that the infection stimulates ATP synthesis in the infected cell, with a peak of ATP levels occurring midway through the infection cycle, when most of the metabolically active bacteria are proliferating. The infection also stimulates synthesis of glutamate with a similar time course as for ATP. The stimulation is apparently due to an enhancement in glucose consumption by the infected cell, which also results in an increased rate of lactate production and glutamate synthesis as well as higher glycogen accumulation during the infection. Concurrently, infection leads to an increase in the expression of the glucose transporter, GLUT-1, on HeLa cells, which may account for the enhanced glucose consumption. The chlamydiae are thus able to stimulate glucose transport in the host cell sufficiently to compensate for the extra energy load on the cell represented by the infection.

The glycyl-tRNA synthetase of Chlamydia trachomatis

Aminoacyl-tRNA synthetases specifically charge tRNAs with their cognate amino acids. A prototype for the most complex aminoacyl-tRNA synthetases is the four-subunit glycyl-tRNA synthetase from Escherichia coli, encoded by two open reading frames. We examined the glycyl-tRNA synthetase gene from Chlamydia trachomatis, a genetically isolated bacterium, and identified only a single open reading frame for the chlamydial homolog (glyQS). This is the first report of a prokaryotic glycyl-tRNA synthetase encoded by a single gene.

Persistence of antichlamydial antibodies after treatment of acute salpingitis with doxycycline

The effect of treatment with doxycycline on serum IgG and IgA antichlamydial antibodies was evaluated in 33 women who had had acute salpingitis associated with high titers of serum IgG (> or = 1:128) and/or IgA (> or = 1:16) antichlamydial antibodies. Overall, 29 women (87.9%) remained with high titers of IgG and/or IgA antibodies. No change or insignificant change in IgG antibody titer was demonstrated in 21 women (63.6%) and in IgA antibody titer in 21 women (63.6%). Positive seroconversion or a significant increase (> or = 4-fold) in IgG antibody titer was demonstrated in eight women (24.2%) and in IgA antibody titer in six women (18.1%). Negative seroconversion or a significant decrease in IgG antibody titer was demonstrated in four women (12.1%) and in IgA antibody titer in six women (18.1%). It is concluded that in most patients who had acute salpingitis associated with pretreatment high titers of serum antichlamydial antibodies, posttreatment titers may remain high even if treatment with doxycycline results in complete resolution of clinical signs and symptoms of the disease.

Heat shock response of murine Chlamydia trachomatis

We have investigated the heat shock response in the mouse pneumonitis strain of Chlamydia trachomatis. The kinetics of the chlamydial heat shock response resembled that of other procaryotes: the induction was rapid, occurring over a 5- to 10-min time period, and was regulated at the level of transcription. Immunoblot analysis and immunoprecipitations with heterologous antisera to the heat shock proteins DnaK and GroEL demonstrated that the rate of synthesis, but not the absolute amount of these two proteins, increased after heat shock. Using a general screen for genes whose mRNAs are induced by heat shock, we identified and cloned two of these. DNA sequence analysis demonstrated that one of the genes is a homolog of dnaK. Further sequence analysis of the region upstream of the dnaK gene revealed that the chlamydial homolog of the grpE gene is located just adjacent to the dnaK gene. The second locus encoded three potential nonoverlapping open reading frames. One of the open reading frames was 52% homologous to the ribosomal protein S18 of Escherichia coli and thus presumably encodes the chlamydial homolog. Interestingly, this ribosomal protein is not known to be induced by heat shock in E. coli. S1 nuclease and primer extension analyses located the start site of the dnaK transcript to the last nucleotide of the grpE coding sequence, suggesting that these two genes, although tandemly arranged, are transcribed separately. No promoter sequences resembling the E. coli consensus heat shock promoter could be identified upstream of either the C. trachomatis dnaK, grpE, or S18 gene. The induction of the dnaK and S18 mRNAs by heat shock occurred at a transcriptional level; their induction could be blocked by rifampin. The mechanisms of induction for these two loci were not the same, however; they were differentially sensitive to chloramphenicol. Whereas the induction of dnaK mRNA required de novo protein synthesis, the induction of the S18 mRNA did not. Thus, C. trachomatis utilizes at least two different pathways to induce the transcription of mRNAs encoding proteins induced in the heat shock response.

Growth of Chlamydia trachomatis in enucleated cells

Chlamydia trachomatis is an obligate intracellular parasite of eucaryotic cells. Little is known about the role of the host in supporting chlamydial replication beyond the facts that host cells provide ATP and that de novo host protein synthesis is not required for bacterial growth. To further explore potential contributions of host nuclear function to chlamydial development, we questioned whether murine C. trachomatis could grow in mouse L cells that had been enucleated with cytochalasin B. Following enucleation, cells were infected with chlamydiae and analyzed morphologically and biochemically. Late in infection, substantial numbers of chlamydiae of all developmental stages were seen within large cytoplasmic inclusions that were indistinguishable from those seen in infected intact cells. Normal numbers of infectious progeny particles were produced from enucleated cultures. We conclude that active host cell nuclear function is not required to support the growth of chlamydiae.

Cloning and characterization of RNA polymerase core subunits of Chlamydia trachomatis by using the polymerase chain reaction

Taking advantage of sequence conservation of portions of the alpha, beta, and beta' subunits of RNA polymerase of bacteria and plant chloroplasts, we have designed degenerate oligonucleotides corresponding to these domains and used these synthetic DNA sequences as primers in a polymerase chain reaction to amplify DNA sequences from the chlamydial genome. The polymerase chain reaction products were used as a probe to recover the genomic fragments encoding the beta subunit and the 5' portion of the beta' subunit from a library of cloned murine Chlamydia trachomatis DNA. Similar attempts to recover the alpha subunit were unsuccessful. Sequence analysis demonstrated that the beta subunit of RNA polymerase was located between genes encoding the L7/L12 ribosomal protein and the beta' subunit of RNA polymerase; this organization is reminiscent of the rpoBC operon of Escherichia coli. The C. trachomatis beta subunit overproduced in E. coli was used as an antigen in rabbits to make a polyclonal antibody to this subunit. Although this polyclonal antibody specifically immunoprecipitated the beta subunit from Chlamydia-infected cells, it did not immunoprecipitate core or holoenzyme. Immunoblots with this antibody demonstrated that the beta subunit appeared early in infection.

A polymerase chain reaction-based approach to cloning sigma factors from eubacteria and its application to the isolation of a sigma-70 homolog from Chlamydia trachomatis

Taking advantage of the known sequence conservation of portions of bacterial sigma factor proteins, we have designed degenerate oligonucleotides corresponding to these domains and used these synthetic DNA sequences as primers in a polymerase chain reaction (PCR) to amplify DNA sequences from the chlamydial genome. The PCR products were used as a probe to recover the genomic fragments from a library of cloned murine Chlamydia trachomatis DNA. Sequence analysis of one of these clones revealed striking homology to the sigma-70 protein of Escherichia coli and the sigma-43 protein of Bacillus subtilis, strongly implying that this locus (sigA) encodes the major vegetative sigma factor of murine C. trachomatis. This PCR-based approach will be broadly applicable to the cloning of major sigma factors from other eubacteria.

Identification of genus-specific epitopes on the outer membrane complexes of Chlamydia trachomatis and Chlamydia psittaci immunotypes 1 and 2

Polyclonal and monoclonal antibodies were used to study the immunogenic and antigenic characteristics of chlamydiae. We focused on the most predominant proteins in the outer membrane complex, the major outer membrane protein (MOMP) and the doublet consisting of proteins of 57 and 62 kilodaltons (57-62 kDa doublet). Immunoblot analyses were performed with chlamydial elementary bodies by using (i) immune sera from sheep which had undergone a recent episode of abortion due to the ovine abortion (OA) strain of C. psittaci, (ii) rabbit hyperimmune anti-C. psittaci (OA) and -C. trachomatis sera, and (iii) monoclonal antibodies to the MOMP of C. trachomatis. The typical pattern of response with polyclonal antisera against heterologous elementary bodies was reactivity with the 57-62 kDa doublet and lipopolysaccharide with weak and sometimes no anti-MOMP activity. Three distinct genus-specific anti-C. trachomatis MOMP monoclonal antibodies showed different patterns of reactivity with the MOMPs of the two immunotypes of C. psittaci and C. trachomatis serovars. Our data confirm the predominance of a genus-specific 57-62 kDa doublet response despite the presence of genus-specific epitopes on the MOMP.

Pulsed-field gel electrophoresis determination of the genome size of obligate intracellular bacteria belonging to the genera Chlamydia, Rickettsiella, and Porochlamydia

The chromosome length of obligate intracellular procaryotes was determined by pulsed-field gel electrophoresis of intact or NotI- and SfiI-restricted genomes. Sizes averaged 2,100, 1,720, 1,550, 2,650, and 1,450 kilobases for Rickettsiella grylli, Rickettsiella melolonthae, Porochlamydia buthi, Porochlamydia chironomi, and Chlamydia psittaci and Chlamydia trachomatis, respectively. An SfiI restriction map of the R. melolonthae genome was derived.

Chlamydial gene encoding a 70-kilodalton antigen in Escherichia coli: analysis of expression signals and identification of the gene product

In an attempt to identify chlamydial genes whose native promoters allow them to be expressed in Escherichia coli, we isolated and characterized a chlamydial gene identified by screening a library of chlamydial DNA with antichlamydial antibodies. This gene encodes a 70-kilodalton immunoreactive polypeptide in E. coli hosts. Sequence analysis of the 5' portion of the gene identified its product as the chlamydial homolog of the E. coli ribosomal protein S1. The site of transcription initiation of the mRNA in chlamydiae was determined, and its putative promoter regions were identified. These regions apparently do not function efficiently in E. coli; in vitro transcripts generated by using E. coli RNA polymerase did not start at the authentic chlamydial initiation site. Several in vitro transcripts both larger and smaller than the authentic transcript were seen; presumably, these transcripts result from adventitious promoterlike elements in adjacent chlamydial DNA and may be responsible for the expression of the gene in E. coli.

Protein synthesis early in the developmental cycle of Chlamydia psittaci

The incorporation of [35S]methionine into protein by intracellular and host-free Chlamydia psittaci 6BC was analyzed at intervals between 15 min and 28 h postinfection by autoradiography of sodium dodecyl sulfate-polyacrylamide gels. The profiles of proteins synthesized in the two systems were similar at all times, indicating that the host-free system can be used to monitor the temporal expression of genes in chlamydiae. The host-free system permitted detection of synthesis of chlamydial proteins as early as 15 min postinfection. Some of the proteins synthesized during the initial phases of reorganization of elementary bodies to reticulate bodies either were not synthesized or were synthesized in greatly reduced amounts during the other phases of the developmental cycle. The effects of rifampin and actinomycin D indicated that host-free protein synthesis was at least partially dependent on the initiation and continuation of RNA synthesis in the isolated organisms.

Experimental chlamydial keratitis in rabbits. Correlation with chlamydia infected McCoy tissue culture cells

Rabbit corneas were inoculated three times at weekly intervals with the agent of chlamydia trachomatis using the scratch method. Specimens of the corneal epithelium were obtained using the replica technique on the 1st, 2nd, 3rd and 4th day after each inoculation and at two weeks after the last inoculation. The development of chlamydial inclusions and the inflammatory cell response were monitored using Giemsa stain, acridine orange stain and direct immunofluorescent technique. Primary inoculation produced mild clinical disease associated cytologically with polymorphonuclear leucocytic cellular inflammatory response. Repeated inoculations produced more severe disease associated clinically with pannus formation and cytologically with the presence of lymphocytes and Leber cells in addition to polymorphonuclear leucocytes. Halberstaedter Prowazek inclusion bodies were detected in all the specimens. Additional intracytoplasmic and intranuclear inclusions of different morphological appearances were present. The cytological findings detected in the corneal epithelium of rabbits were correlated with the findings in McCoy tissue culture cells inoculated with chlamydia trachomatis.

Chlamydial rRNA operons: gene organization and identification of putative tandem promoters

We isolated and characterized the rRNA operons of murine Chlamydia trachomatis. By exhaustively screening a library of chlamydial DNA and by blot hybridization of genomic DNA, we showed that there are only two rRNA operons in C. trachomatis. S1 nuclease protection and primer extension analysis were used to map the 5' and 3' ends of the mature 16S and 23S transcripts in both rRNA cistrons and, additionally, to demonstrate the lack of intervening sequences in these genes. The 5' ends of the presumed primary rRNA transcript were located and found to originate at two tandem sites separated by 100 base pairs. The two tandem chlamydial rDNA transcripts were not differentially regulated. Their products were coordinately expressed and were detectable as early as 9 h postinfection. However, the upstream transcript was only 10% as abundant as the downstream transcript. The sequences surrounding the transcription initiation sites bore little homology with each other or with the classic Escherichia coli -10 and -35 promoter sequences. This finding suggests that chlamydial transcription signals may differ from those of previously studied procaryotes.

Chlamydial hemagglutinin identified as lipopolysaccharide

Chlamydial lipopolysaccharide (LPS) agglutinated mouse and rabbit erythrocytes but not human, guinea pig, or pronghorn antelope erythrocytes. Hemagglutination was not specific for Chlamydia spp., as rough LPSs from Coxiella burnetii and Escherichia coli also agglutinated erythrocytes from the same animal species. Nonagglutinated and agglutinated erythrocytes bound equivalent amounts of LPS, indicating that hemagglutination was not due to a specific interaction of chlamydial LPS with erythrocytes. Thus, hemagglutination by chlamydial LPS is not mediated by specific receptor-ligand interactions but is a property of the altered surface of the LPS-coated erythrocytes.

Ultrastructural study of mode of entry of Chlamydia psittaci into L-929 cells

The entry of Chlamydia psittaci into L-929 cells was studied morphologically by transmission electron microscopy and quantitatively by a method that discriminates between attachment and uptake. Upon adsorption of 3H-labeled elementary bodies (EBs) to host cells at 4 degrees C, the EBs bound efficiently to the L-cell surface. Binding reached an equilibrium level of 55% in 3 h. Ultrastructural analysis revealed that EBs were bound preferentially to the tips and sides of microvilli at this temperature. The EBs were also observed in coated pits located at the bases of microvilli and along smooth surfaces of the host cell. No internalization was observed at 4 degrees C. When cells with prebound 3H-labeled EBs were warmed to 37 degrees C, the EBs rapidly became resistant to proteinase K removal (half time = 5 min), indicating ingested chlamydiae. At 37 degrees C, the EBs were internalized within tightly bound vesicles surrounded by an electron-dense coat of fibrillar material. EBs were also present in smooth-surfaced pits and vesicles of the host cell. Using alpha 2-macroglobulin coupled to colloidal gold (a known marker for receptor-mediated endocytosis), we observed that the entry of EBs into cells via coated pits was identical in appearance to the internalization of alpha 2-macroglobulin. Also, when the two ligands were mixed together, they could be seen within the same coated pits and were cointernalized within endocytic vesicles of the host cell. These results suggest that C. psittaci can enter nonprofessional phagocytic cells by a pathway which is similar to that of receptor-mediated endocytosis of many physiologically important macromolecules, bacterial toxins, and viruses.

Identification and properties of chlamydial polypeptides that bind eucaryotic cell surface components

An electroblotting technique was used to identify proteins of Chlamydia that bound surface-radioiodinated and Triton X-100-solubilized HeLa cell extracts. Two proteins, with apparent molecular masses of 18 and 32 kilodaltons (kDa), that bound HeLa cell surface components were identified on Chlamydia trachomatis L2 elementary bodies (EBs). Radioiodinated heparin, which disrupts chlamydial association with cultured cells, was also bound by these proteins. These two proteins were found on EBs but were absent or were present in reduced amounts on the noninfectious reticulate bodies. All C. trachomatis strains tested displayed two such proteins, although the apparent molecular weight of the larger protein varied with serotype in correlation with biotype and the disease that it caused. Two Chlamydia psittaci strains examined displayed only a single binding protein in the range of 17 to 19 kDa. All of the binding proteins stained intensely and distinctively on silver-stained sodium dodecyl sulfate-polyacrylamide gels and displayed an unusual sensitivity to reducing agents. The 32-kDa protein was not seen and did not bind 125I-labeled HeLa cell components if the EBs were solubilized in the presence of 2-mercaptoethanol. The 32-kDa protein was not affected by dithiothreitol, however. Similar to the effect of 2-mercaptoethanol, the 32-kDa protein was not visualized after treatment of EBs with the protease inhibitors tosyl-phenylalanine chloromethyl ketone (TPCK) or tosyl-lysine chloromethyl ketone (TLCK). TPCK and TLCK also abolished infectivity as did the alkylating agents N-ethylmaleimide and iodoacetamide, yet the latter two agents did not affect the appearance of the 32-kDa protein. These proteins were not detected in immunoblots with either rabbit antisera to C. trachomatis L2 EBs or by serum from a patient with lymphogranuloma venereum. The role of these proteins in the interaction of chlamydiae with host cells is not clear, but the binding of eucaryotic cell surface components and heparin, presence only during the infectious stage of the life cycle, variation between serotypes in correlation with disease, and sensitivity to reducing agents or protease inhibitors, collectively, suggest a role for these proteins in parasite-host interactions.

Effect of polybrene on isolation of Chlamydia trachomatis from clinical specimens

Polybrene treatment of McCoy cells was used to increase the infectivity of Chlamydia trachomatis in vitro. The isolation rate for C. trachomatis in 500 specimens from males and females attending a sexually transmitted disease clinic and other clinics increased by 6.8% with the Polybrene treatment. The data also suggested that this treatment facilitated the diagnosis of low grade or latent infections.

Inhibition of Chlamydia trachomatis growth in McCoy, HeLa, and human prostate cells by zinc

Zinc salts (10(-4) and 10(-5) M) inhibited the number of Chlamydia trachomatis inclusions in McCoy, HeLa, and primary human prostate epithelial cell cultures. Addition of zinc salts 1 h before or 24 h after inoculation with C. trachomatis was found to inhibit growth. Both C. trachomatis serotype D and a lymphogranuloma venereum strain were inhibited by the zinc salts. Although the mechanism of inhibition is not known, the continued presence of the zinc appeared necessary for maximal effect. At the concentrations tested, zinc was not directly toxic to the McCoy cells. These results suggest that the levels of zinc in prostatic secretions may be sufficient to preclude the recovery of chlamydia in the diagnostic laboratory or to inhibit chlamydia from infecting the prostate in vivo.

Effect of proteolytic cleavage of surface-exposed proteins on infectivity of Chlamydia trachomatis

The proteolytic cleavage of Chlamydia trachomatis LGV-434 surface proteins and resultant effects on infectivity and association with cultured human epithelial (HeLa) cells have been examined. Of several proteases examined, trypsin, chymotrypsin, and thermolysin extensively cleaved the chlamydial major outer membrane protein (MOMP). Two proteases, trypsin and thermolysin, cleaved the MOMP to the extent that monomeric MOMP was not detectable by immunoblotting with monospecific polyclonal antibodies. In the case of thermolysin, not even antigenic fragments were detected. Surprisingly, infectivity toward HeLa cells was not diminished. In addition, the association of intrinsically 14C-radiolabeled elementary bodies (EBs) with HeLa cells or their dissociation by proteinase K was not measurably affected by prior trypsinization of the EBs. Trypsinization of lactoperoxidase surface-iodinated elementary bodies demonstrated that most of the 125I-labeled surface proteins were cleaved. In all cases, however, a number of proteolytic cleavage fragments remained associated with the EB surface after surface proteolysis. When trypsinized EBs were electrophoresed under nonreducing conditions and immunoblotted with either polyclonal or type-specific monoclonal MOMP antibodies, MOMP was found in a large oligomeric form that failed to enter the polyacrylamide stacking gel. Additionally, trypsinized viable EBs bound radioiodinated type-specific MOMP monoclonal antibody as efficiently as did the control nontrypsinized organisms. Taken together, the findings indicate that although the MOMP is highly susceptible to surface proteolysis, the supramolecular structure of the protein on the EB surface is apparently maintained by disulfide interactions. Thus, if surface-exposed chlamydial proteins are involved in the initial interaction of chlamydiae with eucaryotic cells, the functional domains of these proteins which mediate this interaction must be resistant to proteolysis and remain associated with the EB surface.

Partial amino acid sequence and molecular cloning of the encoding gene for the major outer membrane protein of Chlamydia trachomatis

The first 25 N-terminal amino acids of the major outer membrane protein of Chlamydia trachomatis serovar L2 were determined. The amino acid sequence was used to construct an oligonucleotide probe specific for the major outer membrane protein gene. Using this oligonucleotide as a hybridization major outer membrane protein gene. Using this oligonucleotide as a hybridization probe, we discovered one recombinant clone that produced a 15-kilodalton polypeptide which reacted with a monoclonal antibody directed against the major outer membrane protein type-specific epitope. In a separate set of experiments, we uncovered another recombinant clone that produced a 51-kilodalton polypeptide which was reactive with an anti-major outer membrane protein subspecies-specific monoclonal antibody. The expression of these recombinant DNA plasmids in Escherichia coli is discussed.

Disulfide-mediated interactions of the chlamydial major outer membrane protein: role in the differentiation of chlamydiae?

The effects of exogenous reducing agents on a number of biological properties of purified Chlamydia trachomatis LGV-434 and Chlamydia psittaci meningopneumonitis elementary bodies (EBs) have been examined in an attempt to identify in vitro correlates of early events in the differentiation of the infectious EB to the replicative cell type, the reticulate body (RB). Treatment of EBs with dithiothreitol elicited a number of changes normally associated with differentiation to the RB. EBs in the presence of 10 mM dithiothreitol displayed enhanced rates of [14C]glutamate oxidation, reduced infectivity, and decreased osmotic stability, and their Machiavello staining properties changed to those characteristic of the RB. A true differentiation of EB to RB did not take place under these conditions, since EBs treated in this manner and examined by transmission electron microscopy did not demonstrate increased size or decreased electron density as do isolated RBs. Additional studies were initiated to identify the macromolecules involved in this process. With polyacrylamide gel electrophoresis and immunoblotting procedures with monoclonal and polyclonal monospecific antibodies, the chlamydial major outer membrane protein was found to be the predominant component that varied under reducing versus nonreducing conditions. Furthermore, the extent of disulfide-mediated cross-linking of the major outer membrane protein varied between the infective and replicative forms of the C. trachomatis LGV-434 life cycle. Implications of disulfide interactions in the life cycle of chlamydiae are discussed.

Enhancement of Chlamydia trachomatis infectious progeny by cultivation of HeLa 229 cells treated with DEAE-dextran and cycloheximide

The effects of DEAE-dextran and cycloheximide on the infection of HeLa 229 cells with Chlamydia trachomatis serotype G were studied in terms of the number of cells infected and the yield of infectious progeny per infected cell. Pretreatment of the host cells with DEAE-dextran resulted in an increase in the number of infected cels but had no significant effect on the yield of infectious progeny per infected cell (burst size). In contrast, the addition of cycloheximide to the medium of infected cells had no significant effect on the number of infected cells but greatly enhanced the burst size. The burst size was calculated to be close to 500. The enhanced burst size was also observed in cells treated with DEAE-dextran and cycloheximide. In addition, there was an increase in the number of cells infected and an augmentation of the infectious progeny yield. Under the conditions of combined treatment, the yield of C. trachomatis serotype G cultivated in HeLa 229 cells was found to be approximately threefold higher than the yield of the organisms cultivated in McCoy cells. The results suggest that HeLa 229 cells treated with DEAE-dextran and cycloheximide offer a most suitable system for the high-yield cultivation of C. trachomatis organisms and possibly also for the diagnosis of infection with these organisms.

Role of disulfide bonding in outer membrane structure and permeability in Chlamydia trachomatis

The outer membrane of Chlamydia trachomatis can be efficiently solubilized by a variety of mild detergents in the presence of the reducing agent dithiothreitol. This allows purification of the chlamydial major outer membrane protein at high yield in very gentle conditions by using its differential solubility in Sarkosyl and octylglucoside in the presence of dithiothreitol. The major outer membrane protein of the L2 serovar is an acidic protein with a pI of ca. 5. It contains three cysteine residues that allow it to form a disulfide-linked proteinaceous network responsible for the characteristic rigid outer membrane of the elementary body. By the use of an in vitro reconstitution assay developed by Nikaido and his co-workers, it was shown that the outer membrane contains pores with an "exclusion limit" between molecular weights 850 and 2,250. In addition, the "opening-closing" of the pores was shown to be controlled through a simple reduction-oxidation mechanism. A model that outlines the role of disulfide bonding in the physiology of chlamydial development is presented.

Characterization of Chlamydia DNA by restriction endonuclease cleavage

The DNA from six serovars of Chlamydia trachomatis, lymphogranuloma venereum (LGV) I, LGV II, LGV III, B, C, and D, and from Chlamydia psittaci was extracted, treated with restriction endonuclease enzymes, and run on agarose gels. By using this technique, the DNA of C. trachomatis could be clearly differentiated from C. psittaci DNA. A comparison of the DNA from the different serovars of C. trachomatis revealed similar patterns with and without detectable differences. LGV I, LGV II, LGV III, B, and C revealed no differences when treated with BamHI, HaeIII, XbaI, and XhoI. LGV III DNA, when cleaved with EcoRI and HhaI, had a major band migrating faster than the other two LGV serovars. Serovar D had a different pattern from all other strains tested when cleaved with BamHI, EcoRI, HhaI, HincI, and XhoI. When treated with SacI and HgaI, LGV II displayed a unique band not seen in the other LGV serovars. Differences in strains could be attributed to both chromosomal and plasmid DNA.

Effect of methylamine and monodansylcadaverine on the susceptibility of McCoy cells to Chlamydia trachomatis infection

We used inhibitors of receptor-mediated endocytosis to study the mechanisms of infectivity, especially the uptake mechanism, of Chlamydia trachomatis for cultured cells. The effect of methylamine and monodansylcadaverine on the different stages of the chlamydial growth cycle in McCoy cells was examined. There was a dose-related decrease in the number of chlamydial inclusions in the presence of these agents. Monodansylcadaverine also decreased the chlamydia-dependent uptake of radioactive amino acids. The agents did not affect the attachment of chlamydiae to the cells, but they increased the protease-removable fraction of cell-bound chlamydiae. The amines reduced the number of inclusions when added at different times during the first 24 h of infection. However, this effect was influenced by host cell density, so that the effect of the amines at the early infectious phase was nullified in confluent monolayers, whereas, during later phases, the effect was comparatively independent of host cell density. This indicates that the amines have different modes of action at different infectious stages. The effect of the amines was reversible, and they had no effect on the infectivity of pretreated chlamydial elementary bodies. These experiments suggest that methylamine and monodansylcadaverine inhibit both the internalization of chlamydiae into McCoy cells and their intracellular development. These results are consistent with the hypothesis that chlamydiae utilize a constitutive cellular process, such as receptor-mediated endocytosis, to enter cells.

Physicochemical surface properties of elementary bodies from different serotypes of chlamydia trachomatis and their interaction with mouse fibroblasts

Aqueous biphasic partitioning, hydrophobic interaction chromatography, and ion-exchange chromatography were used to characterize the surface properties of Renografin-purified elementary bodies of Chlamydia trachomatis serotypes E and L1. The two serotypes differed with respect to liability to hydrophobic interaction and negative surface charge. Furthermore, the mutual relative magnitude of these parameters differed between the two serotypes, depending on the chromatographic technique used. This indicates that these chromatographic techniques register different aspects of charge and hydrophobicity on the chlamydial surface. DEAE-dextran and dextran sulfate affected association of, penetration, and intracellular development of C. trachomatis in mouse fibroblasts (McCoy cells). DEAE-dextran affected the association of C. trachomatis serotype E with McCoy cells mainly by charge-dependent forces, whereas both DEAE-dextran and dextran sulfate influenced the association of C. trachomatis serotype L1 mainly by charge-independent forces. These results indicate that the numerous biological differences between lymphogranuloma venereum and non-lymphogranuloma venereum strains of C. trachomatis may be assigned to differences in surface properties between the two strains.

Effect of cycloheximide on the infective yield of a genital strain of Chlamydia trachomatis in McCoy cells

The yield of infectious progeny of a genital strain of Chlamydia trachomatis in cycloheximide-treated McCoy cell cultures was 11-fold lower than that in untreated monolayers.

Amino acid requirements of a Chlamydia trachomatis genital strain in McCoy cell cultures

Amino acid requirements of a Chlamydia trachomatis were defined in McCoy cell monolayer cultures, depleted of their nutrient reserves by maintenance in Earle balanced salt solution for at least 2 days, and then treated at infection with 1 microgram of cycloheximide per ml, an inhibitor of host cell protein and deoxyribonucleic acid synthesis. Serum-free Waymouth MB 752/1 medium lacking one amino acid or a group of related amino acids was added to depleted cultures before infection. Eight of the amino acids normally present in MB 752/1 were essential for chlamydial growth, six were advantageous for growth, and five were nonessential.

Modifications of the envelope of Chlamydia psittaci during its developmental cycle: freeze-fracture study of complementary replicas

Examination of complementary replicas obtained by freeze-fracture of Chlamydia psittaci revealed, at the level of the plasma membrane, a progressive differentiation of "crate-like formations," which likely correspond to transmembranal pores. Recognition of "early" and "late" stages observed in the intermediate bodies permitted detailed study of the developmental cycle of this chlamydia.