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F O Eko

Publications and source records attributed to F O Eko.

At least 19 recordsLinked to original sources
PubMed2000

Characterization and immunogenicity of Vibrio cholerae ghosts expressing toxin-coregulated pili.

Bacterial ghosts are attractive for use as non-living vaccines and as carriers of heterologous antigens of vaccine relevance. Ghosts were prepared from Vibrio cholerae strains of O1 or O139 serogroup after growth under culture conditions, which favor or repress the production of toxin-coregulated pili (TCP). Immunoblotting confirmed the TCP status of these V. cholerae ghosts (VCG), which retained the cellular morphology and envelope sub-component profile of viable bacteria. Rabbits were immunized with VCGs prepared from O139 bacteria with TCP-positive or TCP-negative phenotypes and the resulting sera assayed for antibodies to lipopolysaccharide (LPS) and to TCP. Regardless of the TCP status of the VCG preparations used for immunization, all animals produced antibodies to LPS as demonstrated in bactericidal assays. These antibodies were probably responsible for the capacity of the antisera to confer passive immunity to challenge with the homologous O139 strain in the infant mouse cholera model (IMCM). Only following immunization with TCP-positive VCG, however, were antibodies to TCP generated, as judged by the potential of antisera to mediate protection against a challenge strain of heterologous serogroup.

Animals↗
PubMed2000

Suppression of endogenous IL-10 gene expression in dendritic cells enhances antigen presentation for specific Th1 induction: potential for cellular vaccine development.

A new paradigm for designing vaccines against certain microbial pathogens, including Chlamydia trachomatis, is based on the induction of local mucosal Th1 response. IL-10 is an anti-inflammatory cytokine that exerts negative immunoregulatory influence on Th1 response. This study investigated whether biochemical modulation of endogenous IL-10 expression at the level of APCs is a practical strategy for enhancing the specific Th1 response against pathogens controlled by Th1 immunity. The results revealed that the high resistance of genetically engineered IL-10-/- (IL-10KO) mice to genital chlamydial infection is a function of the predilection of their APCs to rapidly and preferentially activate a high Th1 response. Thus, in microbiological analysis, IL-10KO mice suffered a shorter duration of infection, less microbial burden, and limited ascending infection than immunocompetent wild-type mice. Also, IL-10KO were resistant to reinfection after 8 wk of the primary infection. Cellular and molecular immunologic evaluation indicated that IL-10KO mice induced greater frequency of chlamydial-specific Th1 response following C. trachomatis infection. Moreover, IL-10KO APCs or antisense IL-10 oligonucleotide-treated wild-type APCs were potent activators of Th1 response from naive or immune T cells. Furthermore, both Ag-pulsed dendritic cells from IL-10KO mice and IL-10 antisense-treated dendritic cells from wild-type mice were efficient cellular vaccines in adoptive immunotherapeutic vaccination against genital chlamydial infection. These findings may furnish a novel immunotherapeutic strategy for boosting the Th1 response against T cell-controlled pathogens and tumors, using IL-10-deficient APCs as vaccine delivery agents.

Adjuvants, Immunologic↗
PubMed1999

Extended recombinant bacterial ghost system.

Controlled expression of cloned PhiX174 gene E in Gram-negative bacteria results in lysis of the bacteria by formation of an E-specific transmembrane tunnel structure built through the cell envelope complex. Bacterial ghosts from a variety of bacteria are used as non-living candidate vaccines. In the recombinant ghost system, foreign proteins are attached on the inside of the inner membrane as fusions with specific anchor sequences. Ghosts have a sealed periplasmic space and the export of proteins into this space vastly extends the capacity of ghosts or recombinant ghosts to function as carriers of foreign antigens. In addition, S-layer proteins forming shell-like self assembly structures can be expressed in candidate vaccine strains prior to E-mediated lysis. Such recombinant S-layer proteins carrying foreign epitopes further extend the possibilities of ghosts as carriers of foreign epitopes. As ghosts have inherent adjuvant properties, they can be used as adjuvants in combination with subunit vaccines. Subunits or other ligands can also be coupled to matrixes like dextran which are used to fill the internal lumen of ghosts. Oral, aerogenic or parenteral immunization of experimental animals with recombinant ghosts induced specific humoral and cellular immune responses against bacterial and target components including protective mucosal immunity. The most relevant advantage of recombinant bacterial ghosts as immunogens is that no inactivation procedures that denature relevant immunogenic determinants are employed in this production. This fact explains the superior quality of ghosts when compared to other inactivated vaccines. The endotoxic component of the outer membrane does not limit the use of ghosts as vaccine candidates but triggers the release of several potent immunoregulatory cytokines. As carriers, there is no limitation in the size of foreign antigens that can be inserted in the membrane and the capacity of all spaces including the membranes, peri-plasma and internal lumen of the ghosts can be fully utilized. This extended recombinant ghost system represents a new strategy for adjuvant free combination vaccines.

Adjuvants, Immunologic↗
PubMed1999

New strategies for combination vaccines based on the extended recombinant bacterial ghost system.

Controlled expression of cloned PhiX174 gene E in Gram-negative bacteria results in lysis of the bacteria by formation of an E-specific transmembrane tunnel structure built through the cell envelope complex. Bacterial ghosts have been produced from a great variety of bacteria and are used as non-living candidate vaccines. In the recombinant ghost system, foreign proteins are attached on the inside of the inner membrane as fusions with specific anchor sequences. Ghosts have a sealed periplasmic space and the export of proteins into this space vastly extents the capacity of ghosts or recombinant ghosts to function as carriers of foreign antigens, immunomodulators or other substances. In addition, S-layer proteins forming shell-like self assembly structures can be expressed in bacterial candidate vaccine strains prior to E-mediated lysis. Such recombinant S-layer proteins carrying inserts of foreign epitopes of up to 600 amino acids within the flexible surface loop areas of the S-layer further extend the possibilities of ghosts as carriers of foreign epitopes. As ghosts do not need the addition of adjuvants to induce immunity in experimental animals they can also be used as carriers or targeting vehicles or as adjuvants in combination with subunit vaccines. Matrixes like dextran which can be used to fill the internal lumen of ghosts can be substituted with various ligands to bind the subunit or other materials of interest. Oral, aerogenic or parenteral immunization of experimental animals with recombinant ghosts induced specific humoral and cellular immune responses against bacterial and target components including protective mucosal immunity. The most relevant advantage of ghosts and recombinant bacterial ghosts as immunogens is that no inactivation procedures that denature relevant immunogenic determinants are employed in the production of ghosts. This fact explains the superior quality of ghosts when compared to other inactivated vaccines. As carriers of foreign antigens there is no limitation in the size of foreign antigens to be inserted and the capacity of all spaces including the membranes, periplasma and internal lumen of the ghosts can be fully utilized. Using the different building blocks and combining them into the recombinant ghost system represents a new strategy for adjuvant free combination vaccines.

Adjuvants, Immunologic↗
PubMed1999

Faecal excretion of Vibrio cholerae during convalescence of cholera patients in Calabar, Nigeria.

The pattern of faecal excretion of Vibrio cholerae was studied over a duration of eight months among 13 cholera convalescents by two-weekly surveillance cultures. Stools and rectal swabs were cultured on Thiosulphate citrate bile salts sucrose (TCBS) agar for the recovery of vibrio pathogens. Clinical phase and convalescent phase V. cholerae strains were compared for antibiogram profiles. The population of vibrios recovered from faecal inocula was usually scanty (<10(3) vibrios/g). All clinical isolates except three were concordant with convalescent phase strains. Sensitivity to tetracycline was uniform for concordant V. cholerae strains, with minimum inhibitory concentration (MIC) ranging from 0.54-4.0 microg/ml. Nine (69.2%) of the convalescents had positive faecal cultures for periods ranging from two weeks to more than seven months. Two adults whose excretions lasted several months also tested positive for human immuno-deficiency virus (HIV) infections. The significance of stool surveillance cultures for identifying asymptomatic infections among convalescents who may need chemotherapy to abolish excretion is emphasised. However, it could not be established with certainty if vibrios excreted during convalescence were from enteric colonization by the causative strains, or re-infections with the common strains in circulation.

Adolescent↗
PubMed1997

Bacterial ghosts as multifunctional vaccine particles.

Expression of cloned PhiX174 gene E in Gram-negative bacteria results in lysis of the bacteria by formation of an E-specific transmembrane tunnel structure built through the cell envelope complex. Bacterial ghosts have been produced from a variety of bacteria including Escherichia coli. Salmonella typhimurium, Salmonella enteritidis, Vibrio cholerae, Klebsiella pneumoniae, Actinobacillus pleuropneumoniae, Haemophilus influenzae, Pasteurella haemolytica, Pasteurella multocida, and Helicobacter pylori. Such ghosts are used as non-living candidate vaccines and represent an alternative to heat or chemically inactivated bacteria. In recombinant ghosts, foreign proteins can be inserted into the inner membrane prior to E-mediated lysis via specific N-, or C-, or N- and C-terminal anchor sequences. The export of proteins into the periplasmic space or the expression of recombinant S-layer proteins vastly extents the capacity of ghosts or recombinant ghosts as carriers of foreign epitopes or proteins. Oral, aerogenic or parenteral applications of (recombinant) ghosts in experimental animals induced specific humoral and cellular immune responses against bacterial and target components including protective mucosal immunity. The most relevant advantage of ghosts and recombinant bacterial ghosts as immunogens is that no inactivation procedures that denature relevant immunogenic determinants are employed in the production of ghosts used as vaccines or as carriers of relevant antigens. The inserted target antigens into the inner membrane or into S-layer proteins are not limited in size.

Adjuvants, Immunologic↗
PubMed1996

Bacterial ghosts: non-living candidate vaccines.

Expression of cloned PhiX174 gene E in bacteria results in lysis of bacteria. It is unique among phage lysis systems as it introduces a transmembrane tunnel structure through the cell envelope complex of Gram-negative bacteria. The resulting bacterial ghosts have intact envelope structures devoid of cytoplasmic contents. E-mediated lysis has been achieved in a variety of Gram-negative bacteria including Escherichia coli, Salmonella typhimurium, Vibrio cholerae, Klebsiella pneumoniae, and Actinobacillus pleuropneumoniae. Such ghosts, derived from human or animal pathogens, have been proposed as non-living candidate vaccines and represent an alternative to heat or chemically inactivated bacteria. In 'recombinant ghosts', foreign proteins (e.g., viral proteins) are inserted into the inner membrane via specific N-, or C-, or N- and C-terminal anchor sequences prior to lysis. Relevant advantages of (recombinant) bacterial ghosts as immunogens include: (i) inactivation procedures that denature relevant immunogenic determinants are not employed in the production of ghosts used as vaccines or as carriers of relevant antigens; (ii) the recombinant proteins are inserted into a highly immune stimulatory environment; (iii) there is no size limitation of the foreign protein moieties: multiple antigenic determinants can be presented simultaneously; (iv) bacterial ghosts can be produced inexpensively in large quantities; (v) (recombinant) ghosts are stable for long periods of time and do not require the cold chain storage system. Intraperitoneal, subcutaneous or intramuscular applications of recombinant ghosts in experimental animals induced specific humoral and cellular immune responses against bacterial and viral components. Initial aerosol vaccinations of swine with ghosts from Actinobacillus pleuropneumoniae showed that protective immunity can be established by this route of application and that the well-preserved surface structures of ghosts obtained by E-mediated lysis are able to target the mucosal immune system.

Animals↗
PubMed1995

Aeromonads in acute diarrhoea and asymptomatic infections in Nigerian children.

Stool samples of 616 asymptomatic and 296 diarrhoeic school children were compared for the recovery rate of Aeromonas spp. on ampicillin (10 micrograms/ml) sheep blood agar. Culture filtrates of isolates were tested for haemolysin production with 1% freshly washed rabbit erythrocytes. Stools of 9 (3.0%) diarrhoeic children yielded five strains of A. hydrophila and four of A. veronii (two each of biotypes sobria and veronii), compared to 12 (1.9%) (p > 0.01) asymptomatic children who harbored seven A. hydrophila and five A. caviae strains. Isolates from-diarrhoeic stools were exclusively from children < or = 5 years, while all infected asymptomatic children were > or = 6 years. Culture filtrates of all nine diarrhoeic strains were uniformly enterotoxigenic (intestinal weight ratio > 0.083) and produced haemolysin titres > 128. These phenotypes where variable in carriage strains of A. hydrophila but were not detected in A. caviae. The recovery of A. hydrophila, and A. veronii biotypes from diarrhoeic stools of children < or = 5 years may suggest their involvement in diarrhoea causation in the absence of other diarrhoeagenic agents.

Acute Disease↗
PubMed1994

Production of Vibrio cholerae ghosts (VCG) by expression of a cloned phage lysis gene: potential for vaccine development.

The protein E-specific lysis mechanism of the Escherichia coli-specific bacteriophage PhiX174 was employed to produce Vibrio cholerae ghosts (VCG). VCG consist of both rounded and collapsed cells that have lost their cytoplasmic contents through an E-specific hole in the cell envelope. These ghosts are proposed as non-living material for immunization against cholera. A specific membrane anchor sequence was used to insert the human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) fusion protein into the cell envelope of V. cholerae. The identity of the expression products was confirmed by Western blot analysis employing an RT-specific monoclonal antibody. HIV-1 RT was chosen as a model for the purpose of evaluating heterologous gene expression in V. cholerae and the carrier potential of VCG. Intraperitoneal immunization of mice was used to evaluate the immunogenic potential of VCG. Preliminary results showed significant seroconversions to intact whole-cell vibrio antigens in mice immunized with VCG or a heat-killed whole-cell vibrio preparation.

Animals↗
PubMed1994

Immunogenicity of Vibrio cholerae ghosts following intraperitoneal immunization of mice.

The immunogenic potential of Vibrio cholerae ghosts (VCG) in comparison with heat-killed whole-cell vibrios (WCV) was evaluated after intraperitoneal immunization of adult mice. Swiss white mice received four doses of VCG or WCV intraperitoneally, consisting of 500 micrograms of lyophilized material in 200 microliters of phosphate-buffered saline (PBS), pH 7.4. The control group received 200 microliters of PBS. Serum samples were collected from all mice on the day of immunization and on days 14, 24, 35 and 62 postimmunization. Sera were examined for vibriocidal antibodies by the microtitre and tube-dilution methods and Vibrio-specific serum IgG antibodies were assessed by ELISA. IgG antibodies to intact WCV were detected in sera from all animals immunized with VCG or WCV. The response was specific and of high magnitude. Significantly higher antibody responses were obtained when sera from both VCG- and WCV-immunized mice were titrated against VCG. The immunogenicity of VCG in evoking serum IgG responses was higher than that of WCV. However, the immunogenicity of the two antigen preparations was comparable in terms of seroconversion for vibriocidal antibodies. These results demonstrate that VCG administered intraperitoneally evoke Vibrio-specific serum IgG responses as well as vibriocidal antibody activity in mice.

Animals↗
PubMed1994

Epidemiology and spectrum of vibrio diarrheas in the lower cross river basin of Nigeria.

In 1991 a cholera epidemic occurred in Nigeria. The features of this cholera outbreak in a single hospital in Cross River, Nigeria, were examined. Microbiologic techniques included the use of thiosulphate citrate bile-salts sucrose (TCBS) medium for culture of all stool specimens. Vibrio isolates from diarrheic patients included V. cholerae-O1 (75), V. cholerae non-O1 (10) and V. parahaemolyticus (21). The illnesses were diverse, ranging from mild to severe, and in most instances requiring hospitalization, rehydration as well as antibiotic treatment. Eighty patients were hospitalized and six died mainly from hypovolemic shock and acute renal failure arising from excessive fluid loss. The low vibrio-associated mortality observed in this outbreak may have been influenced by the proximity and easy transit access to the health care facilities offered by the teaching hospital. This contrasts with the high mortality figures reported by Health Centers in the rural areas during the same period. Some features of vibrio diarrheas were comparable with those of other enteric pathogens. Poorly developed water and sewage disposal systems, contact with sea water, consumption of fishery products and leftover foods were the main risk factors identified.

Adolescent↗
PubMed1992

Features of cholera and Vibrio parahaemolyticus diarrhoea endemicity in Calabar, Nigeria.

The clinical and epidemiological features of acute vibrio diarrhoeal disease were studied in 881 patients seen at the University of Calabar Teaching Hospital (UCTH), Calabar, Nigeria, between January and December 1989. Stools and rectal swabs of patients and randomly-selected control subjects were microscopically and culturally examined for the presence of enteric pathogens. Households of vibrio diarrhoea cases and matched controls were visited for ecologic studies. Of a total of 108 (12.3%) culturally-confirmed bacterial diarrhoeas, 47 (43.5%) were due to Escherichia coli, 33 (30.6%) to Vibrio cholerae-01 (classical and El Tor biotypes) and V. parahaemolyticus, while shigellae and salmonellae accounted for 29 (26.9%) and 9 (8.3%) cases, respectively. Most cholera case households clustered within the ancient neighbourhood of the inner city, characterized by poorly developed water and sewage disposal systems. A preponderance of vibrio diarrhoea patients were children < or = 10 years. Adult cases involved mostly females. The only case of diarrhoea-related death involved an eight-month old child with kwashiorkor and V. parahaemolyticus infection. Incidence of vibrio diarrhoeas was seasonal, with most cases occurring during the dry season followed by subsidence at the onset of rainy season. Bimodal peaks of vibrio diarrhoeal episodes observed over the period appeared to coincide with periods of acute water scarcity, high temperature, increased fishing activities and trade traffic on the Calabar River estuary. Of the environments sampled, only clam shells from a case household and river sediments yielded vibrio pathogens on culture. Ecological factors that are capable of stabilizing a focus of vibrio diarrhoea endemicity in this area are highlighted.

Adolescent↗
PubMed1992

Haemagglutinating and buccal epithelial cell adherence activities of Vibrio parahaemolyticus: correlation with virulence.

Clinical and environmental isolates of Vibrio parahaemolyticus were examined for their ability to agglutinate human and rabbit erythrocyte and to adhere to human buccal epithelial (HBE) cells in the presence or absence of mannose. All strains produced cell-associated haemagglutinins (HGs) after 3 h at 37 degrees C. Mannose-sensitive haemagglutination (MSHA) appeared to be a significant marker for differentiating between clinical and environmental isolates; 75% of clinical and 11% of environmental isolates exhibited MSHA with rabbit erythrocytes. All strains showed mannose-resistant adhesion (MRA) to HBE cells whose pattern had no relationship to the epidemiological source of the isolates. Adherence to HBE cells correlated with haemagglutination (HA) capability of environmental but not clinical isolates. This suggests that although intestinal adherence may be an essential step in vibrio colonization, it may not be a sufficient prerequisite for the subsequent expression of pathogenicity in Vibrio parahaemolyticus.

Animals↗
PubMed1991

Occurrence of Plesiomonas shigelloides--associated diarrhoea in Calabar, Nigeria.

The prevalence, clinical profiles and virulence factors of Plesiomonas shigelloides were determined in patients attending the University of Calabar Teaching Hospital, Microbiology Laboratory. P. shigelloides was isolated from 12 (1.4%) of 880 patients with diarrhoea and from none of the controls (P less than 0.05). Isolates were mostly from febrile children less than or equal to 10 years with most of the infections occurring during the rainy months. Although our findings suggest the significance of Plesiomonas in acute diarrhoea in this environment, our isolates did not seem to show any of the proxy indicators of virulence usually associated with other enteric pathogens.

Adolescent↗
PubMed1991

Antimicrobial resistance trends of shigellae isolates from Calabar, Nigeria.

During a 3-year study (January 1986-December 1988), stools of 2200 diarrhoeal or dysenteric patients were examined by culturing and 108 (4.9%) were found positive for shigellae. Shigella flexneri was the commonest species isolated (54.6%), followed by Sh. dysenteriae (24.1%). Patients aged less than or equal to 15 years accounted for 51.4% of cases. Shigellae over the 3 years showed high and sometimes rising resistance to ampicillin, chloramphenicol, streptomycin and cotrimoxazole and complete resistance to tetracyclines and sulphonamides. Sh. sonnei strains isolated in 1986 and 1987 were almost invariably sensitive to all antimicrobial agents except ampicillin, while in 1988 strains were resistant to all. The isolation rate was higher (74.1%) during the dry season than in the rainy season (25.9%) (P less than 0.01). Low standards of community and personal hygiene and improper sewage disposal are the prevailing epidemiological factors identified.

Adolescent↗
PubMed1990

Comparative study of the prevalence and clinical profiles of diarrheas due to Aeromonas and other enteric pathogens.

The prevalence of Aeromonas spp. and other enteric pathogens in stool specimens from diarrheic and non-diarrheic patients was studied over a 12 month period (January to December, 1986). Except for the absence of fever, all the clinical features in Aeromonas diarrhea were comparable to those associated with other diarrheagenic agents. These features included abdominal pain (30%), vomiting (24.5%), fever (31.5%), dehydration (9.5%) and hematochezia (19.5%). Aeromonas spp. were more frequently isolated from patients with gastroenteritis (2.5%) than from control patients (1.0%) (P less than 0.05). Isolates were recovered more often during the dry months (66.7%), than during the wet months (33.3%). Among the enteric pathogens isolated, Aeromonas spp. (2.5%) ranked next to Esch. coli (14.5%) and Shigella spp. (6.3%) in prevalence. Other bacterial isolates included Plesiomonas shigelloides (1.5%) Vibrio spp. (1.0%), Yersinia enterocolitica (1.0%) and Salmonella spp. (1.8%).

Adolescent↗
PubMed1989

Characterization and significance of Aeromonas spp. isolated from diarrhoeic stools in Nigeria.

During a 12-month study period (January-December 1986), 12 Aeromonas strains (eight A. hydrophila and four A. sobria) were isolated from the 400 diarrhoeic and 200 non-diarrhoeic stools examined. Isolates were characterized for frequency of phenotypic properties associated with virulence using the suckling mouse test for enterotoxin assay; haemolysis of rabbit erythrocytes for haemolysin production, and haemagglutination of human group A cells (HA) for presence of colonization factor antigens (CFA). All seven A. hydrophila and three A. sobria strains isolated from diarrhoeic stools produced enterotoxin. All, except one A. sobria strain from a diarrhoeic stool, produced haemolysin in titres greater than 4. Fifty per cent of strains from diarrhoeic stools and 100% of strains from non-diarrhoeic stools were HA positive. All HA reactions were sensitive to mannose and galactose. The frequency of enterotoxin-producing aeromonads was significantly higher (P less than 0.05) in diarrhoeic patients than in non-diarrhoeic controls. There was no significant difference (P greater than 0.05) in the frequency of haemolysin and HA production between diarrhoeic and non-diarrhoeic strains.

Aeromonas↗