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Biomedical subjects

A C Wong

Publications and source records attributed to A C Wong.

At least 37 records · Page 2Linked to original sources
PubMed1995

Influence of culture conditions on biofilm formation by Escherichia coli O157:H7.

Biofilms of Escherichia coli O157:H7 were developed on stainless steel chips in trypticase soy broth (TSB), 1/5 dilution of TSB, 0.1% Bacto peptone (BP) and a minimal salts medium (MSM) supplemented with 0.04% of one of the following carbon sources: glucose, glycerol, lactose, mannose, succinic acid, sodium pyruvate or lactic acid. It was found that biofilms developed faster and a higher number of adherent cells (ca. 10(6) CFU/cm2) were recovered when the organisms were grown in the low nutrient media. Regardless of the carbon source, biofilms developed in MSM consisted of shorter bacterial cells and thicker extracellular matrix (ECM), with glucose as the best substrate for stable biofilm formation. Fewer bacteria in initial attachment, non-hydrophobicity of bacterial cells, lack of ECM formation and easy detachment of the biofilm bacteria may contribute to poor biofilm formation in TSB. ECM is probably important for the stability of biofilms; however, at 10 degrees C and under anaerobic conditions, ECM seems to be unnecessary.

Anaerobiosis↗
PubMed1995

Identification and purification of a new staphylococcal enterotoxin, H.

A staphylococcal enterotoxin which elicited an emetic response in monkeys but did not share antigenic determinants with any of the identified enterotoxins was identified and purified from Staphylococcus aureus FRI-569. The emetic activity of this new enterotoxin was neutralized only by antibodies specific to it and not by antibodies to enterotoxins A, B, C, D, and E or toxic shock syndrome toxin 1. Immunodiffusion assays did not detect cross-reactivity between this new and all the other identified enterotoxins. The purification procedure involved removal of the enterotoxin from culture supernatant fluids by batch adsorption with CG-50 resin, CM-Sepharose FL ion-exchange chromatography, and Sephacryl 100 HR and Bio-Gel P-30 gel filtration. The molecular weight of this enterotoxin, 27,300, determined by gel filtration on Sephacryl 100 HR agreed with the molecular weight, 28,500, determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The apparent migration of this enterotoxin determined by SDS-PAGE did not shift in the presence of a disulfide reducing agent, indicating that it is composed of a single-chain protein. The N-terminal amino acid sequence of the enterotoxin was determined to be Glu-Asp-Leu-His-Asp-Lys-Ser-Glu-Leu-Thr-Asp-Leu-Ala-Leu-Ala-Asn-Ala-Tyr- Gly- Gln-Tyr-Asn-His-Pro-Phe-Ile-Lys-Glu-Asn-Ile, which did not match the N-terminal sequences of any known proteins. The isoelectric point of the enterotoxin determined by isoelectric focusing was about 5.7.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1995

Enterotoxic activity of hemolysin BL from Bacillus cereus.

Bacillus cereus causes exotoxin-mediated diarrheal food poisoning. Hemolysin BL (HBL) is a well-characterized B. cereus toxin composed of three components (B, L1, and L2) that together possess hemolytic, cytotoxic, dermonecrotic, and vascular permeability activities. Here, we show that HBL causes fluid accumulation in ligated rabbit ileal loops at a dose of 5 micrograms of each component per loop. Maximal fluid responses occurred for combinations of all three components at > or = 25 micrograms of each component per loop. Individual components and binary combinations did not cause significant fluid accumulation at 25 micrograms of each component. Specific antisera to HBL components inhibited the fluid accumulation response of crude culture supernatant from B. cereus F837/76. These antisera were tested against an antiserum to a partially characterized multicomponent diarrheal toxin described previously by Thompson et al. (N. E. Thompson, M. J. Ketterhagen, M. S. Bergdoll, and E. J. Shantz, Infect. Immun. 43:887-894, 1984). Immunoblot and immunoprecipitation analyses indicate that HBL and that toxin are identical. These results confirm previous speculation that HBL is a tripartite enterotoxin that, as for all of its other known activities, requires all three components for maximal activity.

Animals↗
PubMed1995

Extracellular virulence factors in Bacillus cereus endophthalmitis: methods and implication of involvement of hemolysin BL.

Bacillus cereus is a common cause of highly fulminant posttraumatic and metastatic endophthalmitis. Exotoxins or enzymes likely contribute to the severity of the infection, but specific virulence factors have not been identified. We developed two methods for the identification of B. cereus ocular virulence factors. In an in vitro assay that allows screening of multiple samples, retinal toxicity was estimated by measuring the release of lactate dehydrogenase from retinal buttons treated with B. cereus toxins. The results from this assay were confirmed with a sterile endophthalmitis model in which the histopathologic effect of intravitreally injected toxins was assessed. We tested pure hemolysin BL (HBL), a tripartite dermonecrotic vascular permeability factor of B. cereus, and crude exotoxin (CET) preparations, consisting of concentrated, cell-free B. cereus culture supernatant. In the in vitro assay, both CET and HBL caused rapid release of lactate dehydrogenase and retinal disintegration. In vivo, the toxins caused endophthalmitis clinically characteristic of B. cereus within 4 h. Histological changes included rapid retinal necrosis and detachment, choroidal edema, detachment and disruption of the retinal pigment epithelium, and rapid infiltration of polymorphonuclear leukocytes. Neutralization of HBL in CET preparations inhibited toxicity in vitro by 54%, and pure HBL was less toxic than CET with equal HBL contents in both methods. The results suggest that B. cereus ocular virulence is multifactorial and that HBL contributes to virulence.

Animals↗
PubMed1994

Competitive exclusion of Salmonella enteritidis in chicks by treatment with a single culture plus dietary lactose.

Oral inoculation of lactose utilizing cecal bacteria plus 2.5% lactose treatments were tested in young chicks for protective efficacy against infection by Salmonella enteritidis. One-day-old chicks were treated with cecal bacteria upon arrival and challenged orally on day 3 with 10(4)-10(6) cfu S. enteritidis. A single culture identified as Escherichia coli O75:H10 was found significantly more protective than all other isolates tested. This isolate excreted a metabolite(s) in vitro that was inhibitory towards the growth of S. enteritidis. The results of this study indicate that discovery of protective strains can be facilitated by screening isolates in vitro for lactose utilization and growth inhibition of S. enteritidis before administration of treatment.

Administration, Oral↗
PubMed1994

Effect of trisodium phosphate on biofilm and planktonic cells of Campylobacter jejuni, Escherichia coli O157: H7, Listeria monocytogenes and Salmonella typhimurium.

Trisodium phosphate (TSP) has been approved by the United States Department of Agriculture as a post-chill antimicrobial treatment for raw poultry. This study examines the effectiveness of TSP against planktonic (suspended) and biofilm (attached) cells of Campylobacter jejuni, Escherichia coli O157:H7, Listeria monocytogenes and Salmonella typhimurium at room temperature (RT) and 10 degrees C. At either temperature E. coli O157:H7 was the most sensitive to TSP treatments; 10(6) cfu/ml of planktonic or 10(5) cfu/cm2 of biofilm cells were eliminated by a 30 s treatment with 1% TSP. Campylobacter jejuni was slightly less sensitive. Listeria monocytogenes was the most resistant to the effect of TSP, requiring exposure to 8% TSP for 10 min (RT) or 20 min (10 degrees C) to reduce biofilm bacteria by at least one log. Biofilm cells of S. typhimurium and Listeria monocytogenes were more resistant than planktonic cells. Salmonella typhimurium was more sensitive to treatments using TSP at 10 degrees C than at RT. In contrast, L. monocytogenes was more resistant to TSP at 10 degrees C. Trisodium phosphate appears to be an effective treatment for reducing populations of C. jejuni, E. coli O157:H7 and S. typhimurium. This product has the potential to be used for reduction of bacterial counts on other food products besides raw poultry or on food and non-food contact surfaces.

Animals↗
PubMed1994

Identification and analysis of the antigens detected by two commercial Bacillus cereus diarrheal enterotoxin immunoassay kits.

The usefulness of two commercial immunoassays for the detection of diarrheal enterotoxin of Bacillus cereus is unclear because the identity of the enterotoxin(s) has not been proven and the kits detect different proteins. We found that the Bacillus cereus Enterotoxin-Reversed Passive Latex Agglutination kit (Oxoid) detects the L2 component from hemolysin BL, and the Bacillus Diarrhoeal Enterotoxin Visual Immunoassay (Tecra) detects two apparently nontoxic proteins.

Agglutination Tests↗
PubMed1994

Inhibition of Campylobacter jejuni colonization in chicks by defined competitive exclusion bacteria.

Campylobacter enteritis in humans has been linked to consumption of chicken. Reducing Campylobacter jejuni colonization in chickens can potentially reduce Campylobacter infections in humans. In this study, the reduction of C. jejuni colonization in chicks by oral administration of defined competitive exclusion (CE) cultures, 2.5% dietary carbohydrates, or CE cultures and carbohydrates was examined. Prevention, elimination, or direct challenge of Campylobacter infection was simulated by administering treatments before, after, or at the same time as that of the Campylobacter inoculation. Additionally, the effect of maintaining high levels of protective bacteria was evaluated by administering CE cultures on days 1 and 4 (booster treatment). All treatments reduced C. jejuni colonization. Protection by aerobically grown CE cultures was not statistically different from that by anaerobically grown CE cultures. A combination of Citrobacter diversus 22, Klebsiella pneumoniae 23, and Escherichia coli 25 (CE 3) was the most effective CE treatment. Maintaining high numbers of CE isolates by administering CE boosters did not increase protection. The greatest reduction of Campylobacter colonization was observed in schemes to prevent or eliminate C. jejuni infection. C. jejuni was not detected in the ceca of birds receiving the prevention treatment, CE 3 with mannose, representing a 62% reduction in the colonization rate. The protection factor (PF), a value combining the colonization rate and the level of infection, for CE 3 with mannose was high (> 13.2). Fructo-oligosaccharides alone strongly prevented Campylobacter colonization. Only 8% of the chicks in this group were colonized, with a PF of > 14.3.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1994

Identification of hemolysin BL-producing Bacillus cereus isolates by a discontinuous hemolytic pattern in blood agar.

Bacillus cereus causes distinct exotoxin-mediated diarrheal and emetic food poisoning syndromes and a variety of nongastrointestinal infections. Evidence is accumulating that hemolysin BL is a major B. cereus virulence factor. We describe two methods for detection of hemolysin BL in crude samples and on primary culture media. In the first method, the highly unusual discontinuous hemolysis pattern that is characteristic of pure hemolysin BL was produced in sheep and calf blood agar around wells filled with crude culture supernatant from hemolysin BL-producing strains. In the second method, the pattern was formed surrounding colonies of hemolysin BL-producing strains grown on media consisting of nutrient agar, 0.15 M NaCl, 2% calf serum, and sheep or calf blood. Hemolysin BL production was detected with these methods in 41 of 62 (66%) previously identified B. cereus isolates and in 46 of 136 (34%) presumptive B. cereus isolates from soil. All nine isolates tested that were associated with diarrhea or nongastrointestinal illness were positive for hemolysin BL. The methods presented here are specific, simple, inexpensive, and applicable to the screening of large numbers of samples or isolates.

Agar↗
PubMed1994

Improved purification and characterization of hemolysin BL, a hemolytic dermonecrotic vascular permeability factor from Bacillus cereus.

Bacillus cereus causes diarrheal and emetic food poisoning syndromes as well as a variety of mild to severe infections. A dermonecrotic vascular permeability (VP) factor has been implicated as a virulence factor in these illnesses. Hemolysin BL was previously identified as a unique tripartite hemolysin possessing VP activity. In this study, a high-yield purification scheme, which allowed quantitative characterization of hemolysin BL activity and determination of the molecular weight, pI, and N-terminal sequence of each component, was developed. Milligram quantities of the B, L1, and L2 components were highly purified by a combination of anion-exchange and hydroxylapatite chromatographies. The combined components had VP activity at low doses and were necrotic at higher doses. The toxin exhibited an unusual dose-response zone phenomenon in turbidometric hemolysis assays. Activity increased at doses up to 200 ng/ml, then decreased at doses up to 350 ng/ml, and was constant at doses up to at least 2,500 ng/ml. This behavior may provide an explanation for the unusual discontinuous pattern typical of hemolysin BL in gel diffusion assays. At high concentrations of one or two components, the presence of low amounts of the complementary component(s) resulted in full hemolytic activity. Erythrocytes were protected from lysis by Zn2+ at micromolar concentrations but not by Ca2+ and Mg2+ at concentrations up to 25 mM. These data provide guidelines for future work on this toxin and indicate that hemolysin BL is the dermonecrotic VP factor implicated as a B. cereus virulence factor.

Amino Acid Sequence↗
PubMed1990

Biosynthetic human growth hormone in the treatment of growth hormone deficiency.

A total of 309 previously untreated children with growth hormone deficiency (GHD) (219 boys, 90 girls; mean age 8.4 +/- 3.9 years, range 1.5-19 years) were treated for up to 3 years in an ongoing trial designed to examine the long-term efficacy and safety of biosynthetic somatropin (rhGH). The children were treated with rhGH, 0.06 mg/kg (0.16 IU/kg) three times weekly. In the prepubertal children, the mean height velocity increased during the first year from 3.8 +/- 1.8 cm/year to 8.9 +/- 2.2 cm/year (n = 188). During the second and third years, their height velocities were 7.1 +/- 1.1 (n = 147) and 6.3 +/- 1.2 cm/year (n = 64), respectively. The height velocity SDS increased from -2.5 +/- 1.9 before treatment to 3.1 +/- 2.6 during the first year of treatment in the prepubertal children. The mean pretreatment height velocity in those with idiopathic GHD (3.8 +/- 1.6 cm/year) did not differ from that in children with organic GHD (3.8 +/- 2.3 cm/year). In addition, the height velocities during the first year of therapy did not differ significantly with respect to the aetiology of GHD. For the children who entered puberty during the study, the mean height velocity increased from 3.0 +/- 1.7 cm/year before treatment to 8.4 +/- 2.3 cm/year during the first year of rhGH therapy. In the first year, the height velocity of children with a bone age of less than 5 years (9.4 +/- 2.3 cm/year) was significantly greater than that in children with a bone age of 5-10 years (8.4 +/- 1.8 cm/year) or greater than 10 years (7.8 +/- 2.2 cm/year: p = 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1990

Effect of environmental conditions on production of toxic shock syndrome toxin 1 by Staphylococcus aureus.

The kinetics of toxic shock syndrome toxin 1 (TSST-1) production by Staphylococcus aureus was studied in a fermentor in which aeration rate, atmospheric composition, pH, and temperature were controlled. The toxin was synthesized at a maximal rate during the exponential phase. High bacterial populations were not necessarily accompanied by high TSST-1 yields. Aerobiosis increased TSST-1 production, but excessive aeration had an adverse effect. Addition of CO2 enhanced TSST-1 yield by increasing toxin production rate and efficiency. Cultures with no pH control made more TSST-1 than those maintained at pH 5.5 to 7.5. Maximum TSST-1 yields were obtained when cultures were supplied with air (20 cm3/min) and CO2 (5 cm3/min) via a sintered glass sparger.

Bacterial Toxins↗
PubMed1989

Investigation by improved syringe method of effect of tampons on production in vitro of toxic shock syndrome toxin 1 by Staphylococcus aureus.

Twenty-seven types of commercial tampons from five manufacturers were tested in a sealed-syringe method to determine their effect on the growth of Staphylococcus aureus and the production of toxic shock syndrome toxin 1. In this improvement of the syringe method, the available air is limited to that which is contained within the sealed syringe containing the tampon. The culture medium was buffered, and blood and CO2 were included in the incubation to better simulate the vaginal environment during menstruation. Variables of tampon weight, composition, air volume, and absorbency were examined for their effect on the production of toxic shock syndrome toxin 1. Generally, with the exception of brand E, toxin production in the presence of tampons was equal to or lower than that in a sealed control syringe containing air but no tampon.

Analysis of Variance↗
PubMed1988

Restriction fragment length polymorphism in the interzeta hypervariable region for prenatal diagnosis of non-deletion alpha thalassemia.

A Bam HI restriction fragment length polymorphism in the interzeta hypervariable region (IZ HVR) of the zeta-alpha gene cluster was used for the prenatal diagnosis of a pregnancy at risk for Hb H hydrops fetalis. The parents had zeta-alpha thalassemia 1 and non-deletion alpha thalassemia, respectively, and a previous hydrops was missed using the conventional method of gene detection. In this prenatal diagnosis, linkage to IZ HVR was used to exclude non-deletion alpha thalassemia, and the numbers of zeta and alpha genes in the fetus were quantitated to predict the exact genotype. Confirmation was made by analysis of cord blood at delivery.

Amniocentesis↗
PubMed1988

Restriction fragment length polymorphisms associated with factor VIII:C gene in Chinese.

Twenty-six unrelated hemophilia A and 70 unrelated normal chromosomes in 184 subjects were studied to determine the frequencies of intragenic and intergenic restriction fragment length polymorphisms associated with the factor VIII:C gene. The incidences for positive BclI and BglI polymorphic sites in the Chinese were 82% and 100%, respectively. Both were higher than in other ethnic groups, while the incidence for XbaI polymorphism was 57%, which is similar to that reported in Caucasians. Using the St14.1 probe, two polymorphic TaqI allelic systems in the DXS52 region were detectable, with heterozygous rates of 0.712 (for system I, alleles 1 to 8) and 0.495 (for system II, alpha and beta alleles), respectively. Thus, using a combination of four polymorphisms, it would be possible to offer carrier detection or prenatal diagnosis in 96% of Chinese females at risk.

China↗
PubMed1988

A simple method for the treatment of the inverted nipple.

We introduce a simple method for correcting the inverted nipple in which there is preservation of the lactiferous duct, less surgical invasion, and negligible scar formation. Our method consists of two parts: releasing fibrous tissue around the lactiferous ducts, and keeping the nipple in the everted position with a bolster suture and milk suction pump.

Adolescent↗
PubMed1987

Primary culture of squamous head and neck cancer with and without 3T3 fibroblasts and effect of clinical tumor characteristics on growth in vitro.

Twenty-one tumors from patients with squamous cell carcinoma of the head and neck (SCC H/N) were cultured with and without 3T3 fibroblasts in order to determine whether, on the basis of improved tissue culture medium, 3T3 cells could be deleted without altering growth and cloning efficiency. Thirty-five additional primary SCC H/N specimens, cultured in the presence of 3T3 fibroblasts, were studied to assess the effect of tumor differentiation, site of primary tumor, and site of specimen procurement on growth. The authors conclude that 3T3 cells remain essential for optimal growth and cloning efficiency. Also, 3T3 cells improved the number of successful cultures by 33% to 100% depending on the plating density, and cloning efficiency was improved by 50% in the presence of 3T3 cells. Growth did not correlate with tumor differentiation or site of origin of the tumor specimen. Culture of specimens from the primary site resulted in growth significantly more frequently than culture of specimens obtained from metastatic neck nodes.

Carcinoma, Squamous Cell↗