Biomedical subjects
Publications and source records attributed to L G Rubin.
An 11 year old girl developed progressive upper gastrointestinal ulceration and recurrent episodes of intravenous catheter associated polymicrobial septicaemia. Evaluation failed to establish a cause. After exclusion of the parents and careful surveillance of the patient she improved, supporting the diagnosis of suspected child abuse (a form of Meadow's syndrome).
The potential role of extravascular and intravascular replication was studied in initiation of sustained bacteremia in experimental infection due to Haemophilus influenzae type b. When organs and fluid from rats were cultured after intranasal inoculation of the rats with H. influenzae type b, the organism was not recovered from any putative extravascular focus before development of bacteremia. To evaluate the potential contribution of intravascular replication in initiation of bacteremia due to H. influenzae type b, we obtained serial blood cultures after intravenous or intranasal inoculation. Bacterial counts increased exponentially immediately after intravenous and 12-18 hr after intranasal inoculation. Using the same model system, we observed bacteremia due to Streptococcus pneumoniae after intraperitoneal but not intravenous inoculation. After intraperitoneal inoculation, the magnitude of bacteremia in individual rats did not regularly increase exponentially over time. These findings are consistent with extravascular replication leading to bacteremia due to S. pneumoniae and efficient intravascular replication leading to sustained bacteremia due to H. influenzae type b.
A virulent strain of Haemophilus influenzae type b was used to construct a lambda library of chromosomal DNA in Charon 4, amplified in Escherichia coli. From this library a recombinant (I-69) phage was isolated that contained a 10.2-kilobase-pair fragment of DNA eliciting H. influenzae transformants whose colonies had a distinctive opaque phenotype. Compared with their H. influenzae parent strains the opaque I-69 transformants had two defined cell wall alterations: one in the lipopolysaccharide (greater mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis) and one in the outer membrane proteins. The I-69 transformant of virulent type b strain Rd-/b+ had stable expression of type b capsule. In contrast to strain Rd-/b+, the Rd-/b+/I-69 transformant was serum sensitive in vitro and avirulent in vivo in rats. Thus the potential of H. influenzae type b organisms to cause invasive infection can be substantially attenuated by altering the expression of one or more genes that affect the cell wall composition.
Studies on the pathogenesis of Haemophilus influenzae b infection have used bacteria grown in vitro which are relatively serum-sensitive (using serum devoid of anticapsular antibody) compared to organisms taken from infected hosts. We compared the virulence of relatively serum-sensitive and serum-factor induced serum-resistant H. influenzae b by inoculating rats with organisms having one or the other phenotype. The serum-resistant phenotype was more virulent following intraperitoneal or intravenous inoculation; however, there was no difference in the incidence of colonization or bacteraemia following intranasal inoculation. Furthermore, organisms colonizing the pharynx of rats had the serum-resistant phenotype. Thus, different phenotypes of the same strain of H. influenzae b differed in virulence following parenteral, but not intranasal, inoculation of bacteria. This could be explained by a change from serum-sensitive to serum-resistant phenotype shortly after entering the nasopharynx. The phenotype of micro-organisms grown in vitro may differ from organisms in infected individuals and these differences may be of critical importance in studies of immunity to infection and the pathogenesis of infection.
The isolator 1.5 Microbial Tube (E. I. du Pont de Nemours & Co., Inc., Wilmington, Del.) is a new blood culture system for detection of bacteremia in children which involves lysis of blood cells and direct plating of blood lysate on agar media. Haemophilus influenzae type b is a major pediatric pathogen and may be associated with low-density bacteremia (less than or equal to 50 CFU per ml), yet the clinical data on the efficacy of this system for recovery of H. influenzae b are limited. We used a rat model of H. influenzae b bacteremia and fresh, whole human blood inoculated in vitro with H. influenzae b to compare the 1.5 Microbial Tube and conventional Trypticase soy broth (BBL Microbiology Systems, Cockeysville, Md.) for the detection of low-density H. influenzae b bacteremia. There was a significantly lower recovery of H. influenzae b from blood of bacteremic rats and from in vitro-inoculated human blood by using the 1.5 Microbial Tube than by using Trypticase soy broth. Studies on the mechanism of this lower recovery suggested that the contents of the 1.5 Microbial Tube are toxic to H. influenzae b in the presence of human blood. Additional clinical data are necessary before the 1.5 Microbial Tube can be recommended for detection of low-density H. influenzae b bacteremia.
The successful development and implementation of rational strategies for the prevention of bacterial meningitis should be facilitated by acquiring a more detailed knowledge of its pathophysiology. We have used a biologically relevant rat model of meningitis in conjunction with classical microbial genetics and recombinant DNA technology to investigate the molecular basis of Haemophilus influenzae pathogenicity. These studies aim to define how specific bacterial genes mediate the potential of H. influenzae to colonize the nasopharynx, disseminate within the blood stream and invade the central nervous system. By identifying the state or stages in the pathogenic sequence for which the determinant is critical, this approach should also provide insight into the relevant host defense mechanisms which determine resistance or susceptibility. An understanding of the genetic basis of H. influenzae pathogenicity may develop basic knowledge relevant to the treatment and prevention of bacterial meningitis.
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Possible route(s) by which encapsulated bacteria invade the blood from the nasopharynx include (i) the direct invasion of submucosal blood vessels and (ii) clearance via lymphatics to regional nodes followed by bloodstream invasion. These possibilities were investigated in rats after intranasal inoculation with 10(5) Haemophilus influenzae type b. Within 24 h of inoculation, 10 of 42 rats with sterile blood cultures had similar numbers of H. influenzae b recovered from both cervical (local) and periiliac (distant) lymph nodes, which suggested early bacteremic spread. When virtually continuous blood cultures were obtained for 30 min after inoculation with 10(8) H. influenzae b, early transient bacteremia was documented in four of eight rats. Also, we found no significant difference in bacteremia among rats whose cervical lymph nodes had been removed surgically compared with sham-operated rats. These findings favor the hypothesis of a rapid, perhaps direct invasion of pharyngeal blood vessels as an initial determinant of the systemic spread of H. influenzae b.
A serum antibody response has not been previously demonstrated after infection with Clostridium botulinum. We developed an enzyme immunoassay for measuring serum antibody to C. botulinum toxins A, B, and E. This assay system detected a specific immunoglobulin G and immunoglobulin M antibody response to C. botulinum toxin in two patients with infant botulism.
Documented ampicillin treatment failures of systemic Haemophilus influenzae type b infections have been associated with synthesis of a TEM-1 beta-lactamase. A patient with H. influenzae type b meningitis in whom ampicillin treatment failed is described; the isolate was beta-lactamase-negative according to the cell suspension chromogenic cephalosporin assay. The false-negative result occurred in a strain which elaborated a novel, plasmid-mediated beta-lactamase with characteristics which distinguish it from TEM-1 beta-lactamase. Clinically important ampicillin resistance in H. influenzae type b occurs by mechanisms other than by synthesis of TEM-1 beta-lactamase. Diagnostic microbiology laboratories should perform antibiotic susceptibility tests in addition to tests for beta-lactamase production.
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C56 is known to appear in the fluid phase when zymosan is incubated at 37 degrees C with certain acute phase 'reactor' sera. In the present study, C56 was detected bound to the zymosan particle prior to its appearance free in solution. In reactor sera C56 was formed and released with kinetics similar to that of the generation and decay of a C56-binding site formed when zymosan was incubated with normal serum. Bound and fluid phase C56 was detected only in reactor sera, and was generated only by agents known preferentially to activate the properdin pathway. Elution of C56 from zymosan in hypertonic salt solutions proved to be a convenient step in the partial purification of large amounts of this haemolytically active bimolecular complex.
Disseminated adenovirus infection with fatal hepatic necrosis has been reported in 16 patients, 15 of whom had immunocompromising conditions. Herein we report three patients with AIDS and fatally disseminated adenovirus infection with hepatic necrosis. The median age of these 16 patients was 4.7 years, and their illness was characterized by fever (13 of 16 patients), coagulopathy (10 of 16), lower respiratory tract disease (10 of 16), and gastrointestinal hemorrhage (five of 16) in addition to clinical evidence of hepatitis. The adenoviruses isolated were the commonly found serotypes 1, 2, 3, 5, and 7 for 13 of the 15 cases for which this determination was available. With the high frequency of adenovirus infection in humans and the increasing prevalence of human immunodeficiency virus infection in children, it seems likely that this syndrome will continue to be seen.
There are at least two possible explanations for the observation that inoculation with a single microorganism is generally insufficient to cause infection while inoculation with many organisms may regularly result in infection in a susceptible host. Microorganisms may act cooperatively, with the occurrence of infection resulting from their joint action. Alternatively, each organism of the infecting inoculum may independently possess the potential to cause infection, and, with an inoculum size approximating the 50% infectious dose, infection may result from the survival and multiplication of a single organism. Several lines of experimental data involving several bacterial species strongly support the independent-action, or "single-organism," hypothesis of the pathogenesis of colonization and infection. Available data also support the independent-action hypothesis in the pathogenesis of experimental viral infections. This hypothesis provides an explanation for the occurrence of sporadic episodes of infection.
The traditional treatment of subperiosteal orbital abscess consists of surgical drainage and antibiotic therapy. We successfully treated with antibiotics alone nine children (age range 26 months to 12 years) with clinical signs and symptoms of orbital cellulitis and computerized tomographic (CT) evidence of subperiosteal abscess and contiguous ethmoid sinusitis. Two additional patients successfully treated with nonsurgical therapy were identified retrospectively. All patients were admitted to the pediatric service with normal vision. Their visual function was assessed twice daily during the early stages of their illness. All patients improved with intravenous antibiotic therapy. One additional patient required surgical drainage for persistent pain after 1 week of slow but steady clinical improvement. All other patients were clinically cured with medical therapy alone. Five of the medical "cures" had posttreatment CT, which documented the resolution. No patient had a recurrence. We conclude that orbital subperiosteal abscess, like some other abscesses located elsewhere, may be amenable to non-surgical treatment, or that these patients may have had a phlegmon rather than an abscess and the currently accepted CT criteria for diagnosis of a subperiosteal abscess may require modification. We recommend that children with a subperiosteal abscess from contiguous ethmoidal sinusitis who have no evidence of compromised optic nerve function be given a trial of intravenous antibiotic therapy prior to consideration of surgical drainage.
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It has recently been recognized that neonates may develop pneumonia as a result of Legionella pneumophila. The objective of this study is to characterize the epidemiology, risk factors, diagnosis, clinical features, and outcome of neonatal legionellosis. Review of the literature revealed nine cases of neonatal Legionella infection. Five neonates were term infants and four were preterm. Eight had potential risk factors such as prematurity, congenital heart disease, bronchopulmonary dysplasia, or corticosteroid therapy. Diagnosis was proven by culture in all cases. The main presentation was acute respiratory distress requiring mechanical ventilation. In six infants, the infection had a fatal outcome, including five who were not treated with erythromycin. All the cases were nosocomial, and environmental Legionella was documented in five cases. As has been noted in adults and children with Legionella, early recognition and institution of appropriate therapy are the most important determinants of the prognosis.