Biomedical subjects

K J Cheng

Publications and source records attributed to K J Cheng.

At least 19 recordsLinked to original sources

PubMed1995

Emerging patterns of HIV transmission: the value of alternative surveillance methods.

OBJECTIVE: To assess the current patterns of HIV transmission in Los Angeles County and determine if AIDS surveillance data accurately reflect these patterns. DESIGN: Records-based cohort study. METHODS: The demographic and HIV risk characteristics of persons considered to be recently infected with HIV (CD4+ count > 700 x 10(6)/l) were determined and compared with the characteristics of persons meeting the Centers for Disease Control and Prevention (CDC) 1993 AIDS case definition. Data were obtained for patients with HIV infection enrolled from four HIV outpatient clinics and analyzed between August 1991 and July 1993. RESULTS: The patient cohort included 1857 persons with HIV infection; 1096 (59.1%) met the CDC 1993 AIDS case definition and 134 (7.2%) had a CD4+ lymphocyte count > 700 x 10(6)/l. The median CD4+ count for the group presumed to be recently infected was 809 x 10(6)/l. Persons considered recently infected with HIV were more likely than those meeting the AIDS case definition to be female (26.1 and 14.5%, respectively; P < 0.001), black (28.4 and 18.2%, respectively; P = 0.001), or male homosexual injecting drug users (IDU; 6.7 and 3.4%, respectively; P = 0.05). After controlling for confounding variables by logistic regression, persons recently infected were more likely to be female [adjusted odds ratio (OR), 3.4; 95% confidence interval (CI), 1.8-6.5; P < 0.001], black (adjusted OR, 1.6; 95% CI, 1.1-2.5; P = 0.02) or male homosexual IDU (adjusted OR, 2.4; 95% CI, 1.1-5.2; P = 0.02) than persons with AIDS. CONCLUSIONS: Our results suggest that the HIV epidemic in Los Angeles County is currently advancing into different subpopulations and indicate that the current patterns of HIV transmission in the County are not fully reflected in standard AIDS surveillance activities. However, our data must be interpreted cautiously because of potential selection and misclassification biases. These findings illustrate the benefits of alternative surveillance mechanisms in detecting important changes in HIV transmission and defining groups at risk, especially in jurisdictions without HIV reporting.

Adolescent↗

PubMed1994

A conjugative transfer system for the rumen bacterium, Butyrivibrio fibrisolvens, based on Tn916-mediated transfer of the Staphylococcus aureus plasmid pUB110.

A limitation of genetic studies of the rumen bacterium, Butyrivibrio fibrisolvens, has been the availability of suitable vectors and transfer systems. Using the conjugative tetracycline resistant transposon, Tn916, the Staphylococcus aureus plasmid, pUB110, and the pUB110-based shuttle vector, pUBLRS, a conjugative transfer system was developed for B. fibrisolvens. B fibrisolvens donor strains H17c2 and H17c12, containing Tn916 and pUB110 or pUBLRS, respectively, were used in mating experiments with selected B. fibrisolvens strains. Kanamycin resistant transconjugants, containing pUB110, of strains 193, 194, and 195 were detected at a combined average frequency of 7.78 x 10(-7) per donor and 1.11 x 10(-5) per recipient. Transconjugants of strains 193 and 194, containing pUBLRS, were detected at an average frequency of 1.22 x 10(-6) per donor and 4.70 x 10(-8) per recipient. Southern hybridization analysis confirmed the presence of pUB110 and pUBLRS in transconjugants. Results indicated that Tn916 was necessary for mobilization of pUB110 as transconjugants were not detected when the transposon was absent from the donor strains. The ability to mobilize pUB110 and pUBLRS between B. fibrisolvens strains provides a conjugative transfer system that circumvents problems encountered with electroporation.

Animals↗

PubMed1994

Effect of condensed tannins from birdsfoot trefoil on endoglucanase activity and the digestion of cellulose filter paper by ruminal fungi.

The ruminal fungi Neocallimastix frontalis RE1, Neocallimastix patriciarum 27, Piromyces communis 22, and Orpinomyces joyonii 19-2 were examined for their ability to digest filter paper in the presence of condensed tannins from birdsfoot trefoil (Lotus corniculatus L.). For all four fungi, inhibition of endoglucanases was evident at 100 micrograms condensed tannins.mL-1 with nearly complete inhibition at 300 micrograms condensed tannins.mL-1. At 100 and 200 micrograms condensed tannins.mL-1, the endoglucanase activity of N. frontalis RE1 was greater (P < 0.01) than that of the other three fungal species. Exposure to 100 micrograms condensed tannins.mL-1 did not affect the ability of N. frontalis RE1 or N. patriciarum 27 to digest filter paper, and although digestion was reduced, N. frontalis RE1 and P. communis 22 solubilized more than 20% of the filter paper at 500 micrograms condensed tannins.mL-1. In contrast, O. joyonii 19-2 was virtually unable to digest filter paper at 300 micrograms condensed tannins.L-1. Mycelia of fungi grown with condensed tannins were covered by filamentous material, which may have arisen from the formation of condensed tannin-protein complexes. Less than 86% of the condensed tannins (as measured by the H2SO4 method) were recovered after 120 h of incubation with N. frontalis RE1, P. communis 22, and N. patriciarum 27. The need for detailed studies to examine the ability of ruminal fungi to metabolize condensed tannins is evident.

Animals↗

PubMed1994

Production of 2-aminobutyrate by Megasphaera elsdenii.

Production of the amino acid 2-aminobutyrate was studied in four strains of Megasphaera elsdenii grown on a lactate-based growth medium containing Bacto-casamino acids and yeast extract. Supplementation with threonine increased the production of 2-aminobutyrate in three of the four strains, but no substantial increase in production was noted with serine, methionine, or aspartate, all of which are potential sources for the precursor of 2-aminobutyrate, 2-oxobutyrate. L-Cycloserine, an inhibitor of alanine transaminases, decreased both alanine and 2-aminobutyrate production, suggesting that 2-aminobutyrate synthesis may share the same metabolic pathway as alanine synthesis or that 2-oxobutyrate can act as a substrate for alanine transaminases. Decreases in the production of 2-aminobutyrate were associated with a reduction in the catabolism of branched-chain amino acids in two of the four strains.

Amino Acids↗

PubMed1994

Microbial attachment and feed digestion in the rumen.

Direct microscopic examination of the rumen and its contents shows microbial populations largely attached to feed particles in the digesta. Most feeds contain a surface layer that is resistant to attachment and therefore to digestion. Infiltration of these recalcitrant epidermal layers through damage sites or through focused enzymatic attack is essential for initiation of the digestive process. Proliferation of primary colonizing cells produces glycocalyx-enclosed microcolonies. Secondary colonizers from the ruminal fluid associate with microcolonies, resulting in the formation of multispecies microbial biofilms. These metabolically related organisms associate with their preferred substrates and produce the myriad of enzymes necessary for the digestion of chemically and structurally complex plant tissues. Upon accessing the internal, enzyme-susceptible tissues, microbial "digestive consortia" attach to a variety of nutrients, including protein, cellulose, and starch and digest insoluble feed materials from the inside out. Substances that prevent microbial attachment or promote detachment (e.g., condensed tannins, methylcellulose) can completely inhibit cellulose digestion. As the microbial consortium matures and adapts to a particular type of feed, it becomes inherently stable and its participant microorganisms are notoriously difficult to manipulate due to the impenetrable nature of biofilms. Properties of feed that place constraints on microbial attachment and biofilm formation can have a profound effect on both the rate and extent of feed digestion in the rumen. Developments in feed processing (i.e., chemical and physical), plant breeding, and genetic engineering (both of ruminal microorganisms and plants) that overcome these constraints through the promotion of microbial attachment and biofilm formation could substantially benefit ruminant production.

Animal Feed↗

PubMed1994

Effects of mastication on digestion of whole cereal grains by cattle.

A study was conducted to evaluate the effects of mastication on the physical breakdown and ruminal digestion of whole cereal grains by cattle. Three Hereford cows (initial BW 557 kg; SD, 17) surgically fitted with ruminal and esophageal fistulas were fed 5.5 kg/d (as-fed basis) of whole barley, corn, or wheat in an experiment designed as a 3 x 3 Latin square. Eating time and chews per kilogram of DM were greater (P < .10) for corn than for barley or wheat. Whole corn was substantially damaged after ingestive mastication, and the majority of kernels were broken into small pieces. Many barley and wheat kernels showed signs of dentition, but most kernels remained intact. Less saliva (P < .10) was added to whole wheat than to barley or corn during ingestive mastication. Cattle fed whole barley spent twice (P < .10) as long ruminating per kilogram of DM as those fed corn, with intermediate times for wheat. Less than 30% of the DM disappeared from unmasticated whole grains during 96 h of ruminal incubation. Ingestive mastication increased DM digestion to 53, 69, and 66% for barley, corn, and wheat, respectively. Mastication alters the kinetics of ruminal digestion of unprocessed cereal grains. Combined with the inherent protein and starch digestibilities of the grain, mastication affects the type and extent of processing required to optimize the utilization of cereal grains by cattle. Unlike barley and wheat, corn kernels are extensively damaged during ingestive mastication, reducing the need for physical processing.

Ammonia↗

PubMed1993

Comparison of amylolytic and proteolytic activities of ruminal fungi grown on cereal grains.

Strains of the ruminal fungi Neocallimastix patriciarum, Orpinomyces joyonii, and Piromyces communis were grown on cellobiose and on cereal grains and then examined for proteolytic and amylolytic activities. On cellobiose all three fungi displayed similar activities, with the exception of little amylolytic activity in the cell-associated fraction of N. patriciarum. Growth on the cereal grains barley, corn, and wheat showed differences in proteolytic and amylolytic activities amongst the ruminal fungi and between the cereal grains. The data suggest that while these fungi are capable of fermenting the cereal grains the mode of enzymatic attack varies both with the particular fungus and the type of cereal grain.

Amylases↗

PubMed1993

Effect of the protein matrix on the digestion of cereal grains by ruminal microorganisms.

Experiments were conducted to investigate the role of the protein matrix in the digestion of barley and corn by ruminal microorganisms. Grains, ground and collected on sieves as two particle fractions .25 to .89 mm (small particles) and 2.00 to 3.00 mm (large particles), as well as isolated barley and corn starch granules, were incubated with ruminal inocula. For both grains, digestion of starch in small particles was greater (P < .001) than that of large particles. At 16 and 24 h starch digestion was greater (P < .01) in barley than in corn, for small and large particles. Digestion of barley starch granules did not differ (P > .05) from that of corn starch granules at any incubation time. A 4-h preincubation of small-particle corn and barley with protease increased (P < .001) microbial digestion of starch in corn at 16 h but did not affect digestion of barley. When four ruminally cannulated steers were fed diets containing 80% barley, corn, or wheat or 100% alfalfa hay in a 4 x 4 Latin square experiment, amylolytic activity of ruminal inoculum was higher for steers fed grains than for those fed alfalfa. However, when standardized for total viable counts of bacteria, ruminal amylolytic activity did not differ (P > .05) among diet treatments, but proteolytic activity of ruminal inoculum for steers fed alfalfa was higher (P < .01) than that for steers fed cereal grains. Activity of serine proteases in ruminal inoculum was higher (P < .05) for steers fed alfalfa than for steers fed grains.(ABSTRACT TRUNCATED AT 250 WORDS)

Amylases↗

PubMed1992

Cloning and expression of an amylase gene from Streptococcus bovis in Escherichia coli.

An amylase gene was identified in a Streptococcus bovis 033 lambda gtWES lambda B genomic library. Using a starch overlay and a Congo red-iodine staining procedure, amylase positive clones could be identified by zones of clearing. Ten amylase positive clones were identified using this procedure. The clone chosen for further study, lambda SBA105, contained an insert of approximately 7.5 kb. The insert was mapped, and subcloning localized the amylase gene to a region of approximately 3.1 kb. Cloning of the 3.1 kb amylase fragment into pUC18 in both orientations revealed that the amylase gene was transcribed from its own promoter. Amylase activity was expressed by the Escherichia coli subclones and was found to be largely associated with the cytoplasmic fraction. Southern hybridization of genomic DNA from the amylolytic strains, S. bovis 033, S. bovis 077, Butyrivibrio fibrisolvens 194 and 195 revealed a single hybridizing band in S. bovis 033 DNA only. This indicates that the amylase gene from S. bovis may differ from the amylases of these other amylolytic bacteria.

Amylases↗

PubMed1991

Prevention of fungal colonization and digestion of cellulose by the addition of methylcellulose.

When the attachment of cellulolytic rumen fungi to cellulose is blocked by the addition of methylcellulose, cellulose digestion is entirely inhibited. Even after these fungi have colonized and penetrated the cellulosic fibers of filter paper, the addition of methylcellulose effectively halts cellulose digestion. This effect of methylcellulose is accompanied by the complete inhibition of fungal attachment to cellulose fibers; the addition of methylcellulose does not affect the growth of these organisms on soluble substrates. We conclude that fungal cellulose digestion, like bacterial cellulose digestion, requires the spatial juxtaposition of the cellulolytic organism and its insoluble substrate. The simultaneous inhibition of both attachment and digestion by the same inhibitor suggests that these two processes are functionally linked in the fungi.

Animals↗

PubMed1991

Cloning of a xylanase gene from Fibrobacter succinogenes 135 and its expression in Escherichia coli.

A genomic library consisting of 4- to 7-kb EcoRI DNA fragments from Fibrobacter succinogenes 135 was constructed using a phage vector, lambda gtWES lambda B, and Escherichia coli ED8654 as the host bacterium. Two positive plaques, designated lambda FSX101 and lambda FSX102, were identified. The inserts were 10.5 and 9.8 kb, respectively. A 2.3-kb EcoRI fragment that was subcloned from lambda FSX101 into pBR322 also showed xylanase activity. Southern blot analysis showed that the cloned EcoRI fragment containing the xylanase gene had originated from F. succinogenes 135. The cloned endo-(1,4)-beta-D-xylanase gene (pFSX02) was expressed constitutively in E. coli HB101 when grown on LB and on M9 medium containing either glucose or glycerol as the carbon source. Most of the beta-D-xylanase activity was located in the periplasmic space. Zymogram activity stains of nondenaturing polyacrylamide gels and isoelectric focusing gels showed that several xylanase isoenzymes were present in the periplasmic fraction of the E. coli clone FSX02 and they probably were due to posttranslational modification of a single gene product. Comparison of the FSX02 xylanase and the xylanase from the extracellular culture fluids of F. succinogenes 135 and S85 for their ability to degrade oat spelt xylan showed that, for equal units of beta-D-xylanase activity, hydrolysis by the cloned gene product was more complete. However, unlike the unfractionated mixture of xylanases from F. succinogenes 135 and S85, the enzyme from E. coli FSX02 was unable to release arabinose from oat spelt xylan.

Animals↗

PubMed1991

Selection of a sterilization method for the study of cereal grain digestion.

Experiments were initiated to select a sterilization method(s) that minimizes alterations in the digestive properties of cereal grains and, thus, would be suitable for the study of cereal grain digestion by pure cultures of ruminal bacteria. The following five treatments were examined: unsterilized (U), autoclaving with buffer (AB), autoclaving without buffer (AD), ethylene oxide (E), and gamma irradiation (I). Solubility of DM, starch, and CP was determined by soaking grain in buffer for 1 h followed by filtration through Whatman #54 filter paper. Ground corn and wheat from each treatment were placed in vials with a 1:1 mixture of Bryant's medium and ruminal inoculum. Vials were incubated for 4, 8, 12, 24, and 48 h and analyzed for starch content. Bacterial growth was not evident in sterilized, uninoculated samples. The AD treatment decreased the disappearance of CP in wheat and corn, whereas AB caused an increase in the disappearance of DM, CP, and starch in wheat (P less than .001) compared with U. Rates of microbial starch digestion for corn were 1.3, 1.5, 3.3, 14.7, and 3.5%/h and for wheat were 1.3, 3.4, 4.6, 17.1, and 4.6%/h for AD, E, I, AB, and U, respectively. Contrasts indicated that AD and AB differed (P less than .001) from U for both corn and wheat. It is likely that gelatinization of cereal starch enhanced microbial starch digestion in AB and the formation of Maillard products reduced starch digestion in AD. Corn and wheat sterilized with E or I had digestive properties that closely resembled those of U grain, and either sterilization method was suitable for studying cereal grain digestion.

Animals↗

PubMed1991

Results of angioscopy-assisted intraoperative transluminal angioplasty of the iliac and femoral artery.

Angioscopy as a guide for intraoperative transluminal angioplasty was used in the treatment of 36 arterial occlusive lesions in 32 patients, thirty males and two females with mean age of 67.72 +/- 5.95 years (range from 57 to 75 years). Of these, 19 involved the iliac artery and 17 the femoropopliteal artery. All the intraluminal lesions of the artery were successfully visualized. Patency rate for iliac transluminal angioplasty was 95% at the first year and 85% at the second and third years. For femoropopliteal transluminal angioplasty it was 80% at the sixth month and 72% one to three years after. The results in our series were satisfactory when angioscopy was used as an adjunct to assist intraoperative transluminal angioplasty so that the operation could be done more safely and more time-saving with no significant clinical complications. In view of these encouraging results, we will recommend angioscopy as a specific ancillary technique in certain cases of peripheral vascular disease during concomitant vascular surgery, but long term investigation is necessary.

Aged↗

PubMed1991

Plasma prostanoids in neonatal extracorporeal membrane oxygenation. Influence of meconium aspiration.

Thromboxane B2 may be a mediator of neonatal persistent pulmonary hypertension. Elevated levels of plasma thromboxane and prostacyclin have been described previously in hypoxic newborn infants with neonatal pulmonary hypertension. We measured serial plasma levels of thromboxane B2 and 6-keto-prostaglandin F1 alpha (stable metabolite of prostacyclin) in 21 newborn infants with severe respiratory failure and pulmonary hypertension who required extracorporeal membrane oxygenation support. We sought to study (1) the evolution of plasma prostanoids in pulmonary hypertensive infants treated with extracorporeal membrane oxygenation and (2) whether different pulmonary hypertensive diagnostic subgroups have distinctive prostanoid profiles. Our data indicated that infants with meconium aspiration had significantly lower levels of plasma thromboxane B2 and 6-keto-prostaglandin F1 alpha while receiving extracorporeal membrane oxygenation than did infants with persistent pulmonary hypertension but no meconium aspiration. Levels of all infants decreased progressively as extracorporeal membrane oxygenation support continued.

6-Ketoprostaglandin F1 alpha↗

PubMed1990

Antigenic nature of the chloride-stimulated cellobiosidase and other cellulases of Fibrobacter succinogenes subsp. succinogenes S85 and related fresh isolates.

Polyclonal and monoclonal antibodies to the Cl-stimulated cellobiosidase of Fibrobacter succinogenes subsp. succinogenes S85 reacted with numerous proteins of both higher and lower molecular weights from F. succinogenes subsp. succinogenes S85, but not with Escherichia coli proteins, and only one protein each from Butyrivibrio fibrisolvens and Ruminococcus albus. Different profiles were observed for Western blots (immunoblots) of peptide digests of both the purified enzyme from F. succinogenes and immunoreactive proteins of higher and lower molecular weights, demonstrating that they were different proteins. Therefore, F. succinogenes appeared to produce numerous proteins with one or more common antigenic determinants. However, with the exception of Cl-stimulated cellobiosidase, none were cellulases that have been characterized. An affinity-purified polyclonal antibody to Cl-stimulated cellobiosidase reacted with numerous proteins in cells of each of three fresh isolates of F. succinogenes subsp. succinogenes and one of F. succinogenes subsp. elongata when analyzed by Western blotting. Antibodies to periplasmic cellodextrinase, endoglucanase 2 (EG2), and EG3, when reacted in Western blots with the various cellulases, including Cl-stimulated cellobiosidase, revealed limited antigenic similarity among the different proteins and none with either B. fibrisolvens or R. albus proteins. The periplasmic cellodextrinase antibody reacted with an antigen with a size corresponding to cellodextrinase in each of the three F. succinogenes subsp. succinogenes isolates but not with any antigens from the F. succinogenes subsp. elongata isolate. The anti-EG2 antibody reacted with single antigens in each of the four isolates, while the anti-EG3 antibody reacted with only one of the four isolates.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteroides↗

PubMed1990

Is there a role for lactobacilli in prevention of urogenital and intestinal infections?

This review describes the importance of microbial adhesion in the ecology of the urogenital and intestinal tracts and the influence of host and microbial factors in bacterial interference. In a recent revival of interest in bacterial interference, lactobacillus administration has been studied as a means of treating and preventing disease. Although evidence is conflicting, Lactobacillus acidophilus appears to be involved in beneficial antagonistic and cooperative reactions that interfere with establishment of pathogens in the gastrointestinal tract. The mechanisms of action are believed to involve competitive exclusion and production of inhibitory substances, including bacteriocins. These characteristics, as well as demonstrated adherence abilities in vitro, led to selection of certain Lactobacillus strains for clinical studies of cystitis. Weekly intravaginal Lactobacillus therapy reduced the recurrence rate of uncomplicated lower urinary tract infections in women. Use of Lactobacillus strains resistant to Nonoxynol-9, a spermicide that kills members of the protective normal vaginal flora, may have potential for use in women with recurrent cystitis using this contraceptive agent. In veterinary studies, bacterial interference by administration of probiotics has also been beneficial in disease prevention in animals. Carefully selected bacterial mixtures integrate with the gastrointestinal flora of the animals and can confer disease resistance and improve physiological function. Additional human and animal trials are needed to determine the practical, long-term usefulness of bacterial interference as a protective mechanism against infectious diseases.

Bacterial Physiological Phenomena↗

PubMed1990

Isolation and characterization of cellulolytic anaerobic fungi and associated mycoplasmas from the rumen of a steer fed a roughage diet.

The isolation of 12 strains of cellulolytic fungi from the rumen of a roughage-fed steer is described. These represented three different genera, including one new genus and species (Orpinomyces bovis). The organisms were indistinguishable on the basis of fermentation products from cellulose, and their fermentation patterns were very similar to those of rumen fungi isolated in other countries. Mycoplasmas were found to be associated with 7 of the 12 isolates. The ecological role of the association of the mycoplasmas with rumen fungi is still unknown.

Anaerobiosis↗

PubMed1990

Esterase activity of pure cultures of rumen bacteria as expressed by the hydrolysis of p-nitrophenylpalmitate.

Seventy-four strains of rumen bacteria comprising 20 genera were tested for the ability to hydrolyze p-nitrophenylpalmitate (PNPP-C16). This ability was detectable in all cultures tested, but the level of activity was quite variable. Known lipolytic strains of these bacteria showed generally low levels of activity in this assay, which suggests that the hydrolysis of this artificial substrate indicates a general esterase activity and not a lipase activity, as reported in the literature. The highest activity was found to occur in strains known to be feed-particle-associated digesters of starch, pectin and cellulose. In fractionated rumen contents, p-nitrophenylpalmitase activity was largely associated with feed particles. Although the in vivo role of the enzymes that hydrolyze PNPP-C16 remains obscure, it appears that they are primarily of microbial origin, and may be important in hydrolyzing ester bond-containing compounds from plant material.

Animals↗