Biomedical subjects

G Cassell

Publications and source records attributed to G Cassell.

9 recordsLinked to original sources

PubMed2001

Elevated cytokine and chemokine levels and prolonged pulmonary airflow resistance in a murine Mycoplasma pneumoniae pneumonia model: a microbiologic, histologic, immunologic, and respiratory plethysmographic profile.

Because Mycoplasma pneumoniae is hypothesized to play an important role in reactive airway disease/asthma, a comprehensive murine model of M. pneumoniae lower respiratory infection was established. BALB/c mice were intranasally inoculated once with M. pneumoniae and sacrificed at 0 to 42 days postinoculation. All mice became infected and developed histologic evidence of acute pulmonary inflammation, which cleared by 28 days postinoculation. By contrast, M. pneumoniae persisted in the respiratory tract for the entire 42 days studied. Tumor necrosis factor alpha, gamma interferon, interleukin-6 (IL-6), KC (functional IL-8), MIP-1alpha, and MCP-1/JE concentrations were significantly elevated in bronchoalveolar lavage samples, whereas IL-4 and IL-10 concentrations were not significantly elevated. Pulmonary airflow resistance, as measured by plethysmography, was detected 1 day postinoculation and persisted even after pulmonary inflammation had resolved at day 28. Serum anti-M. pneumoniae immunoglobulin G titers were positive in all mice by 35 days. This mouse model provides a means to investigate the immunopathogenesis of M. pneumoniae infection and its possible role in reactive airway disease/asthma.

Airway Resistance↗

PubMed2000

Dissection of bacteriophage lambda site-specific recombination using synthetic peptide combinatorial libraries.

A wide variety of tools have been used to dissect biochemical pathways, inhibitors being chief among them. Combinatorial approaches have made the search for inhibitors much more efficient. We have applied such an approach to identify hexapeptides which inhibit different steps in a site-specific recombination reaction mediated by the bacteriophage lambda integrase protein. Integrase's mechanism is still incompletely understood, in large part because several pathway intermediates remain hard to isolate. Integrase-catalyzed recombination is very efficient, but if blocked, it is highly reversible to substrates; this combination makes some intermediates exceedingly transient. We have used synthetic peptide combinatorial libraries to screen for hexapeptides that affect the recombination pathway at different stages, and have identified two families of peptides: one probably blocks DNA cleavage, the other may stabilize the Holliday junction intermediates. These peptides do not resemble parts of integrase or any of the other helper functions in the pathway. The deconvolution of hexapeptide libraries based both on inhibition of an enzymatic reaction as well as on accumulation of reaction intermediates is a novel approach to finding useful tools for dissecting a biochemical pathway.

Alanine↗

PubMed2000

Peptide inhibitors of DNA cleavage by tyrosine recombinases and topoisomerases.

The study of biochemical pathways requires the isolation and characterization of each and every intermediate in the pathway. For the site-specific recombination reactions catalyzed by the bacteriophage lambda tyrosine recombinase integrase (Int), this has been difficult because of the high level of efficiency of the reaction, the highly reversible nature of certain reaction steps, and the lack of requirements for high-energy cofactors or metals. By screening synthetic peptide combinatorial libraries, we have identified two related hexapeptides, KWWCRW and KWWWRW, that block the strand-cleavage activity of Int but not the assembly of higher-order intermediates. Although the peptides bind DNA, their inhibitory activity appears to be more specifically targeted to the Int-substrate complex, insofar as inhibition is resistant to high levels of non-specific competitor DNA and the peptides have higher levels of affinity for the Int-DNA substrate complex than for DNA alone. The peptides inhibit the four pathways of Int-mediated recombination with different potencies, suggesting that the interactions of the Int enzyme with its DNA substrates differs among pathways. The KWWCRW and KWWWRW peptides also inhibit vaccinia virus topoisomerase, a type IB enzyme, which is mechanistically and structurally related to Int. The peptides differentially affect the forward and reverse DNA transesterification steps of the vaccinia topoisomerase. They block formation of the covalent vaccinia topoisomerase-DNA intermediate, but have no apparent effect on DNA religation by preformed covalent complexes. The peptides also inhibit Escherichia coli topoisomerase I, a type IA enzyme. Finally, the peptides inhibit the bacteriophage T4 type II topoisomerase and several restriction enzymes with 2000-fold lower potency than they inhibit integrase in the bent-L pathway.

Amino Acid Sequence↗

PubMed1999

The geometry of a synaptic intermediate in a pathway of bacteriophage lambda site-specific recombination.

Bacteriophage lambda uses site-specific recombination to move its DNA into and out of the Escherichia coli genome. The recombination event is mediated by the phage-encoded integrase (Int) at short DNA sequences known as attachment ( att ) sites. Int catalyzes recombination via at least four distinct pathways, distinguishable by their requirements for accessory proteins and by the sequence of their substrates. The simplest recombination reaction catalyzed by Int does not require any accessory proteins and takes place between two attL sites. This reaction proceeds through an intermediate known as the straight-L bimolecular complex (SL-BMC), a stable complex which contains two attL sites synapsed by Int. We have investigated the orientation of the two substrates in the SL-BMC with respect to each other using two independent direct methods, a ligation assay and visualization by atomic force microscopy (AFM). Both show that the two DNA substrates in the complex are arranged in a tetrahedral or nearly square planar alignment skewed towards parallel. The DNA molecules in the complex are bent.

Attachment Sites, Microbiological↗

PubMed1998

Preventing the misuse of microorganisms: the role of the American Society for Microbiology in protecting against biological weapons.

The American Society for Microbiology's (ASM) involvement with issues surrounding biological weapons began during World War II and continues to the present time. The Public and Scientific Affairs Board (PSAB) of the ASM has played an important role in monitoring and responding to legislative and regulatory issues involving biological weapons. As this review makes apparent, there is no consensus of opinion among scientists on their role in biological defense research, or is it likely that there will ever be complete agreement. There is consensus that steps should be taken to prevent biological warfare and that openness of scientific research and global surveillance of disease outbreaks can significantly increase transparency for detecting development of biological weapons. The ASM recommends increased attention to and efforts directed toward global surveillance of disease outbreaks, not only to aid public health organizations in improving human health, but also to establish baseline data against which unusual disease outbreaks can be assessed. Issues of how best to increase global security and to achieve a scientifically based verification protocol of the Biological Weapons Convention are important and continue to be addressed by the ASM.

Biological Warfare↗

PubMed1998

Mycoplasma pneumoniae pneumonia in a mouse model.

To investigate the pathogenesis of acute Mycoplasma pneumoniae infection, BALB/c mice were anesthetized with metofane, and M. pneumoniae was introduced intranasally on days 0, 1, and 2. Mice were sacrificed on days 0-15. A histopathologic scoring system defined inflammatory changes in the lungs on a scale of 0-26 (least to most severe). Broth cultures were positive for all nasal passage and bronchoalveolar lavage (BAL) specimens. Histopathologic scores ranged from 0 to 21. The mean log10 (cfu/mL) were 4.1-6.4 on days 1-10 and >/=1.7 on days 13-15 for nasal passage and BAL specimens. Serum polymerase chain reaction was negative. ELISA for serum IgM and immunoblots for M. pneumoniae antibody were positive in 21 (62%) of 34 and 33 (97%) of 34 infected animals, respectively, at days 8-15. ELISA for IgG antibody was negative. This mouse pneumonia model can be used to study the immunologic and therapeutic responses to acute M. pneumoniae infection.

Animals↗

PubMed1991

Role of Chlamydia pneumoniae in acute chest syndrome of sickle cell disease.

Children with sickle cell disease and acute chest syndrome were investigated for infection with Chlamydia pneumoniae and Mycoplasma pneumoniae. Of 30 patients who had 32 episodes of acute chest syndrome, four (13%) had C. pneumoniae isolated from the nasopharynx; two of these also had serologic evidence of acute infection, and one had positive nasopharyngeal isolates on two subsequent occasions during the course of 1 year with stable, elevated titers of anti-C. pneumoniae IgG, suggesting chronic infection. Two patients with negative cultures had serologic evidence of infection with C. pneumoniae. None of 32 cultures for M. pneumoniae were positive, and although anti-M. pneumoniae IgM developed in two patients, one of these patients had evidence of C. pneumoniae infection (positive culture and seroconversion). We conclude that C. pneumoniae infection is prevalent in our sickle cell population with acute chest syndrome. Until further studies clarify the pathophysiologic significance of C. pneumoniae infection, we believe that early inclusion of erythromycin as antimicrobial therapy for acute chest syndrome seems reasonable.

Adolescent↗

PubMed1990

Extragenital Mycoplasma hominis infections in adults.

PURPOSE: To heighten awareness of the role of Mycoplasma hominis as an extragenital pathogen in adults. PATIENTS AND METHODS AND RESULTS: Patients ranged in age from 14 to 76 years. Thirteen patients were immunosuppressed, including nine organ transplant recipients; three were receiving steroids, and two had an underlying malignancy. The remainder were immunocompetent. Thirteen patients had prior surgery at or near the site of infection. M. hominis was isolated from normally sterile sites such as blood or cerebrospinal, pleural, abdominal and joint fluids, and bone. Non-sterile sites of isolation included surgical wounds and pulmonary secretions. The organism was detected in anaerobic cultures of clinical specimens sent to the laboratory for routine bacteriologic culture. Gram stains of fluids or wound drainage revealed neutrophils but no bacteria. Anti-mycoplasmal therapy was effective in eradicating the organism in 13 of 15 patients who were treated. Of those in whom treatment failed, one patient had an antibiotic-resistant isolate and the other had M. hominis isolated from the lung at postmortem after just 2 days of therapy. CONCLUSION: Our experience suggests that significant infections due to M. hominis, although uncommon, are not rare, and methods to isolate and identify this organism should be available for general adult medical and surgical populations.

Adolescent↗

PubMed1987

Infant pneumonitis associated with cytomegalovirus, Chlamydia, Pneumocystis, and Ureaplasma: follow-up.

A total of 205 infants who were hospitalized when younger than 3 months of age for pneumonitis were followed longitudinally. Of these patients, 145 (70%) had evidence of infection with one or more pathogens. The most common etiologic agents were Chlamydia trachomatis 61/193 (36%), respiratory syncytial virus 33/142 (23%), cytomegalovirus 42/203 (20%), Pneumocystis carinii 30/171 (17%), and Ureaplasma urealyticum 21/125 (16%). The initial clinical presentation was characterized by cough, rales, normal temperature, and diffuse obstructive airways disease by chest roentgenogram. Regardless of etiology, significant association occurred for cough and cytomegalovirus, apnea and Pneumocystis, and conjunctivitis and Chlamydia. Longitudinal follow-up demonstrates a mortality of 7/205 (3.4%). Morbidity was manifest as recurrent wheezing episodes in 86/187 (46%) patients, persistently abnormal chest roentgenographic findings for at least 12 months in 17/109 (15%) patients, and abnormal pulmonary functions in 15/25 (60%) patients. These abnormalities occurred irrespective of prematurity, atopy, or the initial etiologic agent associated with the pneumonitis. These data add further evidence that respiratory infections during infancy may well be predecessors of obstructive airways disease in later life.

Chlamydia Infections↗