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At least 19 recordsLinked to original sources
PubMed2026

Characterization of carABpyrB operon and role of pyrE in Francisella novicida biofilm.

Pyrimidine biosynthesis is essential for bacterial growth, but its role in regulating biofilm formation in Francisella (F.) novicida remains poorly defined. In this study, we experimentally defined the carABpyrB operon in F. novicida and investigated how disruption of the de novo pyrimidine biosynthesis pathway affects growth and biofilm formation under nutrient-restricted conditions. Reverse transcriptase PCR confirmed co-transcription of carA, carB, and pyrB, and promoter prediction identified two putative σ70-dependent promoter regions upstream of carA. Transposon mutants disrupted in carA, carB, and pyrB exhibited pronounced growth defects in Chamberlain's Defined Medium that were restored by uracil supplementation, confirming pyrimidine auxotrophy and functional disruption of de novo pyrimidine biosynthesis. We then extended this analysis to additional genes in the pyrimidine biosynthetic pathway and assessed biofilm formation in modified Mueller-Hinton broth, a nutrient-restricted condition. In this medium, carA, carB, pyrB, and pyrE mutants exhibited growth deficiencies; however, the pyrE mutant uniquely produced significantly more biofilm than the wild type. This phenotype remained evident even without growth normalization, with the pyrE mutant producing 3.3-fold more biofilm than wild type, despite impaired growth, and increased to 11.8-fold when normalized to growth. Quantitative PCR demonstrated that uracil supplementation represses carA, carB, and pyrB transcription, consistent with feedback regulation of the pathway. Together, these findings indicate that pyrimidine limitation is not simply a growth-limiting condition but can alter biofilm regulation, with pyrE disruption revealing a strong association between de novo pyrimidine biosynthesis and biofilm formation.

Biofilms↗
PubMed1977

Virulence factors of Francisella tularensis.

The mechanism causing viable Francisella tularensis to lose virulence in aerosols has been investigated. Fully virulent organisms were found to be encapsulated and avirulent organisms from aged aerosols, decapsulated. Capsules were also removed by suspension of F. tularensis in hypertonic sodium chloride. The resulting naked, but viable, organisms were predominantly avirulent for guinea-pigs challenged intraperitoneally. Capsular material and cell walls were found to contain large amounts of lipid, about 50 and 70% (w/w) respectively, and to differ in lipid and sugar composition. Isolated capsular material was not found to contain a lethal toxin for mice or guinea-pigs, or to induce an immunological response in these animals to fully virulent F. tularensis.

Aerosols↗
PubMed1977

Immunization against tularemia: analysis of the effectiveness of live Francisella tularensis vaccine in prevention of laboratory-acquired tularemia.

A retrospective analysis was made of cases of laboratory-acquired infections with Francisella tularensis among civilian employees at Fort Detrick, Maryland. The incidence and clinical presentation of tularemia during the decade 1950-1959, when the phenol-killed Foshay vaccine was used routinely for immunization of employees, were compared with similar data from the first decade (1960-1969) after the live tularemia vaccine had come into use. The incidence of typhoidal tularemia fell (from 5.70 to 0.27 cases per 1,000 at-risk employee-years; P less than 0.001), whereas the incidence of ulceroglandular tularemia remained unchanged (from 0.76 to 0.54 cases per 1,000 at-risk employee-years). Ulceroglandular tularemia in employees immunized with live vaccine was characterized by clinical signs and symptoms that were milder than those in employees vaccinated with the Foshay vaccine.

Bacterial Vaccines↗
PubMed1975

Phagocytosis of Francisella tularensis by Rhesus monkey peripheral leukocytes.

Phagocytosis of Francisella tularensis by rhesus monkey peripheral neutrophils (PMN, was assessed by autoradiography, electron microscopy, and biochemical techniques. PMN, in contrast to mononuclear phagocytes, were unable to phagocytize F. tularensis in vitro in the absence of immune serum. It is postulated that in the nonimmune host the innate inability of PMN to phagocytize F. tularensis deletes one of the possible mechanisms of host defense to bacterial infection and thus permits the early dissemination of F. tularensis to intracellular sites of specific target tissues.

Animals↗
PubMed1975

Temporal appearance of opsonizing antibody to Francisella tularensis: detection by a radiometabolic assay.

The burst in oxidative metabolism that is mediated through activation of the hexose monophosphate shunt and accompanies particle ingestion by polymorphonuclear leukocytes was used as the indicator in an in vitro radiometabolic assay for detection of specific opsonizing antibody to Francisella tularensis. Release of 14CO2 from radiolabeled glucose was increased significantly when specific immune serum added to suspensions of monkey polymorphonuclear leukocytes and F. tularensis. With this method, opsonizing antibodies to F. tularensis were detected in monkey serum 3 days after vaccination. Significantly increased opsonic activity in these monkeys preceded the appearance of, and persisted longer than, antibody activity as determined by conventional serological techniques. In addition, sera from 11 of 12 humans that were immunized 1 month to 13 years previously and had nondiagnostic agglutinating antibody titers demonstrated significant opsonizing activity.

Animals↗
PubMed1975

Biochemical and immunological properties of ribonucleic acid-rich extracts from Francisella tularensis.

Ribonucleic acid (RNA)-rich extracts derived from the attenuated strain of Francisella tularensis (strain LVS) protected Swiss mice against lethal challenge with F. tularensis strain 425 but not against strain SCHU S4. No killed preparation, including an RNA-rich extract from SCHU S4 itself, offered protection against strain SCHU S4 in contrast to the high level of protection offered against this strain by vaccination with live strain LVS. The protective activity observed against strain 425 was sensitive to ribonuclease but not to Pronase. Protective activity is not a general property of bacterial RNA, since RNA-rich extracts from Staphylococcus aureus offered no protection against tularemia, although disc gel electrophoresis showed similar kinds and amounts of RNA in preparations form F. tularensis and S. aureus. Furthermore, inability to localize activity to a specific region in sucrose gradients suggests a structural rather than an informational role for the RNA in such extracts. RNA-rich extracts from F. tularensis but not from S. aureus were efficient inducers of F. tularensis opsonins in mouse serum, suggesting one mechanism by which such extracts confer protection.

Animals↗
PubMed1978

Stimulation of subpopulations of human lymphocytes by a vaccine strain of Francisella tularensis.

When purified T lymphocytes from individuals vaccinated with a viable, attenuated strain of Francisella tularensis were incubated in vitro in the presence of heat-killed bacteria or a membrane preparation of the vaccine strain, they were stimulated to form blast cells and to synthesize deoxyribonucleic acid. The blast cells had the characteristics of T cells, being devoid of surface immunoglobulin and able to form rosettes with sheep erythrocytes. The stimulation occurred only when monocytes were present. A lymphocyte preparation enriched in B lymphocytes did not respond to the heat-killed bacteria or to the membrane preparation. In a stimulated mononuclear leukocyte preparation, about 70% of the blast cells formed rosettes with sheep erythrocytes, and 10 to 20% of them had surface immunoglobulin. The results show that there is an enlarged population of specifically committed T lymphocytes after tularemia vaccination. It is suggested that the lymphocyte stimulation test measures mainly T-lymphocyte reactivity when membranes or whole bacteria of F. tularensis LVS are used as antigen, and that the stimulation of human T lymphocytes by whole bacteria or bacterial membranes is completely monocyte or macrophage dependent. The present experimental procedure may provide a model for study of antigen-induced stimulation of human lymphocytes under controlled conditions. The technique used gave a reproducible, extremely purified preparation of T lymphocytes and a preparation of monocytes especially suitable for microcultures.

Antigens, Bacterial↗
PubMed1979

Cellular fatty acid composition of Francisella tularensis.

Several unusual fatty acids characterized strains of Francisella tularensis. Long-chain (C20-C26) acids and the hydroxy acids 2-hydroxy-decanoate, 3-hydroxy-hexadecanoate, and 3-hydroxy-octadecanoate appeared to be of special diagnostic value.

Decanoates↗
PubMed1977

Isolation of Francisella tularensis from infected frozen human blood.

Francisella tularensis was isolated from human blood that was frozen for 3 months before it was examined. Before he became ill, the patient operated a "bush-hog" in an area thickly populated with rabbits. His illness was undiagnosed and untreated before his death. Portions of blood and tissue homogenates from necropsy were injected intraperitoneally into mice and inoculated onto glucose-cysteine-blood agar plates. F. tularensis did not grow from the culture plates, but mice inoculated with the blood died in 48 to 72 h. Fluorescent-antibody stains of mouse liver and spleen impression smears showed clumps of cells or amorphous masses of brightly staining envelope material around the cells. Tissue impressions of liver, spleen, and heart blood inoculated onto glucose-cysteine-blood agar yielded pure cultures of F. tularensis.

Agglutination Tests↗
PubMed1975

Chronic shedding tularemia nephritis in rodents: possible relation to occurrence of Francisella tularensis in lotic waters.

Contamination of streams by Francisella tularensis, a fastidious pathogen, was discovered by Miller in Russia. Subsequently that contamination was found to be the source of extensive human outbreaks, and to occur as well in North America. Circumstantial evidence supports a hypothesis that infected voles are responsible for the contamination, but when freshly isolated F. tularensis palaearctica is inoculated parenterally, only acute illness and death result whereas long-term contamination of streams would seem to demand a more chronic process. Laboratory studies have demonstrated that voles have an apparent predilection to tularemic nephritis when partially immunized before parenteral infection, but also when naive voles are infected orally. Associated chronic bacteriuria would seem to fulfill requirements for protracted contamination of watersheds.

Animals↗
PubMed1979

Resistance to tick-borne Francisella tularensis by tick-sensitized rabbits: allergic klendusity.

Mammals become hypersensitive to ticks that feed upon them. That hypersensitivity was thought responsible for an observation that a large number of Francisella tularensis-infected Dermacentor variabilis failed to infect a rabbit previously exposed to ticks of that species. In a series of tests of that hypothesis, rabbits sensitized to ticks were often significantly more resistant than control animals to tick-borne tularemia. The conditions that determine the klendusity are thought to be variable and complex but the phenomenon must be of importance in the epidemiology of some arthropod-borne agents.

Animals↗
PubMed1978

Enigmatic resistance of sheep (Ovis aries) to infection by virulent Francisella tularensis.

Tularemia in range sheep is an occasional cause of severe economic loss from mortality and unthriftiness as well as a hazard to persons in contact with the animals. Epizootics are unpredictable and explosive, therefore, prophylaxis is more practical than therapy. Live vaccine of proven value in man and in beavers was inoculated into mature ewes and elicited antibodies without harm to the sheep. However, challenge of immunity was not possible because virulent Francisella tularensis in large doses did not cause significant mortality in healthy, well managed, unimmunized sheep. Evidence suggests that a complex of stresses such as inclement weather, lambing and concomitant ectoparasitism render sheep more susceptible to tularemia.

Animals↗
PubMed1978

Changes in whole blood and serum components of grivet monkeys with experimental respiratory Francisella tularensis infection.

Grivet monkeys infected with virulent Francisella tularensis Strain Schu S4 showed significant early changes in serum levels of trace metals, triglycerides and activities of alkaline phosphatase, lactate dehydrogenase and alpha-hydroxybutyrate dehydrogenase. Free amino acid levels decreased slightly and there was a marked increase in the phenylalanine: tyrosine ratio. Serum lysozyme activity and seromucoid levels also increased. Kanamycin therapy produced remission of overt signs but the changes in blood constituents were less readily affected. Immunization with the live vaccine strain of F. tularensis induced transient responses similar to those resulting from Schut S4 infection. Immunized monkeys subsequently challenged with the virulent Schu S4 strain showed no clinical signs or marked changes in blood constituents.

Animals↗
PubMed1977

Changes in whole blood and serum components during Francisella tularensis and rabbit pox infections of rabbits.

Rabbits infected with virulent Francisella tularensis strain Schu S4 or rabbit pox virus (Utrecht strain) showed significant early changes in serum levels of trace metals, neutral fat and alkaline phosphatase activity. With F. tularensis infections a marked early leukopenia and a decrease in serum amino acids were also observed; the effect on amino acid levels was less pronounced in rabbit pox infections. In both diseases these changes preceded the appearance of acute phase globulins in the serum. Vaccination with the live vaccine strain of F. tularensis slightly increased survival times but did not delay the onset of metabolic changes in rabbits subsequently infected with the virulent Schu S4 strain.

Alkaline Phosphatase↗