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Biomedical subjects

K J Cheng

Publications and source records attributed to K J Cheng.

At least 91 records · Page 5Linked to original sources
PubMed1981

Formation of bacterial microcolonies on feed particles in the rumen.

Examination of particulate feed that had been digested in vivo in the rumen, and of the leaves of specific legumes that had been digested in vitro by a mixed population of rumen bacteria, showed that very extensive glycocalyx-enclosed bacterial microcolonies developed on many of the available surfaces. Some of these adherent bacteria colonized a surface almost exclusively and attracted another specific type of bacteria as the second members of a distinct morphological consortium. The true extent of the exopolysaccharide glycocalyces of these adherent rumen bacteria was seen in cases where the fibers were attached at multiple points, and their role in microcolony formation and adhesion could be unequivocally ascribed.

Journal Article↗
PubMed1981

Selective isolation and characteristics of Bacteriodes succinogenes from the rumen of a cow.

Eleven isolates of Bacteriodes succinogenes were obtained from the rumen of a cow by an enrichment method with dewaxed cotton fibers as the selective substrate. All of the isolates degraded cotton fibers, but none formed clear zones in cellulose agar, having only a limited ability to degrade the type of cellulose powder used. One isolate, BL2, was studied in greater detail and was found to accumulate a glycogen-like polysaccharide when excess (0.5 to 1.0%) soluble carbohydrate was supplied in the nutrient medium. Although the pattern of growth and polysaccharide accumulation by strain BL2 changed during maintenance of the organism in the laboratory, the maximum amount of carbohydrate found in the cells was constant, at around 74% of the cell dry weight. The findings are discussed in relation to the methods of assessing the role of B. succinogenes in the rumen fermentation.

Animals↗
PubMed1981

A scanning electron microscopy study of the invasion of leaflets of a bloat-safe and a bloat-causing legume by rumen microorganisms.

A newly developed technique using ruthenium red to detect foci of bacterial digestion in mounts of whole leaflets that had been incubated with rumen bacteria was used to compare the digestion of alfalfa, a bloat-causing legume, and sainfoin, a bloat-safe legume. When whole leaflets were suspended in an artificial rumen medium and inoculated with rumen bacteria, massive bacterial adhesion and proliferation were noted at the stomata of alfalfa leaflets after 6 h of incubation, whereas only a few isolated bacteria adhered near the stomata of sainfoin leaflets After 22 h of incubation, the epidermal layers of alfalfa leaflets had peeled away in many areas, revealing an extensive bacterial invasion of the underlying mesophyll tissue in which large bacterial microcolonies had formed in intercellular spaces, and in intracellular spaces in several areas where plant cell walls had broken down. After 22 h of incubation, the surface of sainfoin leaflets resembled that of alfalfa leaflets at 6 h, with bacterial microcolonies adhering to the area surrounding the stomata, but without sloughing of the epidermis. Uninoculated control leaflets of both species showed no surface alteration but part of their normal bacterial flora had proliferated to form microcolonies on the surface after 22 h incubation. Dry matter loss due to leaching or bacterial digestion when whole leaflets of legumes were suspended in an artificial rumen medium, alone or with rumen bacteria, was significantly higher in the bloat-causing group. Values of leaching and of bacterial digestion were positively correlated. We conclude that reported differences in plant anatomy, and in cell wall chemistry, produce distinct rates or organic nutrient release from legume leaflets, and that these same differences produce an equally distinct susceptibility of leaflets to bacterial invasion, plant cell rupture, and the consequent release of intracellular plant components. The rate of release of organic nutrients from legume leaflets may be important in the etiology of foamy pasture bloat. This technique of in vitro digestion of whole leaflets followed by ruthenium red staining shows some promise of providing a rapid and qualitative test to distinguish, within a species, cultivars that may differ in their bloat-related characteristics.

Animal Feed↗
PubMed1981

Identification of rumen bacteria that anaerobically degrade aliphatic nitrotoxins.

Of 33 pure stains of rumen bacteria from the Lethbridge laboratory collection, 5 degraded both 3-nitropropanol (NPOH) and 3-nitropropionic acid (NPA) under anaerobic conditions, and another 5 strains degraded only NPA. The nitroacid was metabolized at a faster rate than the nitroalcohol by both pure cultures of rumen bacteria and mixed rumen microorganisms. Nitrite was detected during incubation of NPOH and of NPA with resting cells but not with growing cultures of active strains of rumen bacteria. Nitrite was metabolized much faster than the nitrotoxins by both pure cultures of rumen bacteria and mixed rumen microorganisms. The results suggest that the nitro moiety of NPA or NPOH is metabolized to inorganic nitrite and nitrite is reduced to ammonia by rumen microorganisms, thereby resulting in its detoxification.

1-Propanol↗
PubMed1981

The role of bacterial surface structures in pathogenesis.

Modern research has revealed that the true surfaces of animal cells consist of polysaccharide chains that are linked to proteins hydrophobically anchored in the membrane and protrude to form a dense glycocalyx. It has become increasingly clear that most pathogenic bacteria must position themselves at the surface of their "target" cell in order to exert their toxic or otherwise deleterious effects. The true surface of most pathogenic bacteria has also been recently shown to consist of a protruding mass of polysaccharide chains--the bacterial glycocalyx--that is composed of teichoic acids in many gram-positive species and of acid polysaccharides in many gram-negative organisms. Through this bacterial glycocalyx certain cell surface proteins and organized protein structures (e.g., pili) are known to project, so that the bacterial surface is a mosaic of polysaccharides and proteins; both of these types of molecules have been implicated in instances of specific pathogenic adhesion. Besides their role in specific adhesion to target cells, these surface components interpose a highly charged, and often very extensive, barrier that can prevent the penetration of antibodies and antibiotics to their target sites in the bacterial cell. They may also frustrate mucociliary clearance, phagocytosis, and other clearance mechanisms of the host. We will discuss the chemical and physical nature of these bacterial surface components that mediate pathogenic adhesion and counteract host defense mechanisms sufficiently to allow infections to become established.

Bacteria↗
PubMed1980

Adherent bacterial populations on the bovine rumen wall: distribution patterns of adherent bacteria.

Fourteen tissue sites from the bovine reticulo-rumen were examined by scanning electron microscopy to determine the distribution patterns of bacterial populations adhering to the epithelium. Although diet variations did not appear to influence the total number of tissue-adherent bacteria present in adult Herefords, diet affected their distribution. It appeared that the distribution of the bacterial populations may be directly affected by the physical state of the digesta. The digesta may be mechanically removing adherent bacteria from the tissue surface by abrasive action. The total adherent population consisted of subpopulations with separate distribution patterns, and macropopulations of morphologically similar bacteria were occasionally observed at specific sites on the epithelial surface. Ureolytic organisms on the epithelium followed a distribution pattern considerably different from the general bacterial distribution.

Animals↗
PubMed1980

Digestion of epithelial tissue of the rumen wall by adherent bacteria in infused and conventionally fed sheep.

Comparisons were made, by light and electron microscopy, of the rumen epithelium of sheep fed conventionally and fed by infusion of volatile fatty acids and buffer into the rumen and casein into the abomasum. Similar bacterial colonization of the epithelium was observed in each case. The mitotic index of epithelial cells in infused sheep was high, as it was in barley-fed animals, while the mitotic index of cells from animals receiving roughage was low. The bacterial flora appeared to be actively digesting the epithelial cells. The fate of sloughed epithelial cells in the rumen fluid of sheep fed by infusion was also studied. The sloughed cells were rapidly digested, probably by their attached flora of facultatively anaerobic, highly proteolytic bacteria, leaving abundant highly keratinized remnants in rumen fluid. The importance of epithelial cell turnover and of proteolysis by partially facultative bacteria in the rumen is discussed.

Animal Feed↗
PubMed1980

Sequence of events in the digestion of fresh legume leaves by rumen bacteria.

When fresh whole leaves of six different species of forage legumes were suspended in an artificial rumen medium and inoculated with rumen bacteria, bacterial adhesion and proliferation were noted at the stomata, and penetration of the stomate by these bacteria was documented by electron microscopy. The invading bacteria adhered to surfaces within the intercellular space of the leaf and produced very extensive exopolysaccharide-enclosed microcolonies. After some of the legume leaf cell walls were disorganized and ruptured by bacterial digestion, these cells (notably, parenchyma and epidermal cells) were invaded by bacteria, with subsequent formation of intracellular microcolonies. However, other cells were neither ruptured nor colonized (notably, stomata guard cells and vascular tissue). At all stages of the digestion of intact legume leaves, the rumen bacteria grew in microcolonies composed of cells of single or mixed morphological types, and a particular ecological niche was often completely and consistently occupied by a very large microcolony of cells of single or mixed morphological types.

Journal Article↗
PubMed1980

The constitutive nature of alkaline phosphatase in rumen bacteria.

Alkaline phosphatase (APase) activity of Megasphaera elsdenii was enhanced by PO4 2- limitation in batch culture; however, six other species of rumen bacteria tested showed no increase in APase activity under these conditions. Alkaline phosphatase was produced by the mixed rumen microflora even though the inorganic phosphorus concentration was as high as 10mM. The APase activity of the bacterial fraction from rumen fluid was not increased during incubation in a phosphorus-free culture medium. Since bacteria may account for greater than 80% of the APase activity in the rumen, this would suggest that the bulk of the APase activity in the rumen is synthesized constitutively. The bacterium responsible for most of the APase activity probably is Bacteroides ruminicola.

Alkaline Phosphatase↗
PubMed1980

The formation of microcolonies by rumen bacteria.

When rumen fluid is fixed for electron microscopy, without centrifugation, a large amount of material sediments spontaneously and ruthenium red staining shows this material to be partially composed of bacterial microcolonies in which morphologically similar sister cells are enclosed in an extensive fibrous exopolysaccharide glycocalyx. The exopolysaccharide matrix condenses, to variable degrees, during the dehydration steps of specimen preparation for electron microscopy but some fibers are stabilized by their attachment to solid surfaces at multiple points and the extent of this matrix can be deduced from morphological data. Even after condensation, the glycocalyces of rumen bacteria occupy more space than the cells themselves and they completely surround most cells with a fibrous matrix, whose chemical composition dictates an ion-exchange function, that must be assumed to be protective against some bacteriophage and antibacterial agents.

Animals↗
PubMed1980

In vitro digestion of bloat-safe and bloat-causing legumes by rumen microorganisms: gas and foam production.

Leaves of three bloat-safe legumes -- birdsfoot trefoil (Lotus corniculatus L.), sainfoin (Onobrychis viciaefolia Scop.), and cicer milkvetch (Astralagus cicer L.) -- and of three bloat-causing legumes -- alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), and white clover (Trifolium repens L.) -- were incubated with strained rumen fluid or with mixed rumen fluid and solids. Gas released was measured during the early period (0 to 22 h) of this in vitro digestion. Gas volume was greater with a 1:1 (wt/vol) mixture of solid and fluid rumen contents than with rumen fluid alone. It was greater with whole and chewed leaves from the bloat-causing legumes than with whole leaves from the bloat-safe legumes. However, when leaves were homogenized, volumes of gas from bloat-causing and bloat-safe legumes were similar. More gas was released from homogenized leaves than from the same weight of whole leaves. The amount of foam produced on chewed herbage and homogenized leaves of bloat-causing legumes was greater than on those of bloat-safe legumes. These results are consistent with the rate of disintegration and digestion of legumes by rumen bacteria being an important determinant in pasture bloat. Measurement of gas produced early in in vitro digestion may provide a useful bioassay for evaluating the bloat-causing potential of legumes in breeding selections if variability of the method can be reduced.

Animals↗
PubMed1979

An independent microbial flora of the epithelium and its role in the ecomicrobiology of the rumen.

IT has been suggested that the bacterial flora of the rumen should be considered as three distinct, interacting populations-the bacteria of rumen fluid (the population which has been studied most extensively), the bacteria associated with food particles, and the bacteria adhering to the epithelial wall of the organ(1). Until now, studies of the 'epithelial' population have been restricted to examination of postmortem samples of wall tissue and its attached bacterial flora(2-5). A recently developed technique(6) for feeding young sheep for long periods solely by infusion of protein and other essential nutrients into the abomasum, and of volatile fatty acids and bicarbonate buffer into the rumen, has provided us with an opportunity to study in isolation the role of the bacterial population of the wall in the ecomicrobiology of the rumen in the living animal. Our studies show that this population can exist independently of the other two populations, that it is primarily responsible for urea digestion in the rumen and that it initiates breakdown of dead epithelial tissue. Furthermore, our results point to an inverse relationship between ammonia concentration and ureolytic activity in rumen fluid, which may account for the control which ammonia exerts over flux of urea across the rumen wall(7-9).

Journal Article↗
PubMed1979

The mechanism of passage of endogenous urea through the rumen wall and the role of ureolytic epithelial bacteria in the urea flux.

1. The rumen urea concentration in gnotobiotic lambs lacking ureolytic bacteria was equal to that of blood. 2. Bacterial urease (EC 3.5.1.5) activity in sheep fed by intraruminal and intra-abomasal infusion was inversely related to rumen ammonia concentration. 3. A model is proposed for the facilitation and control of urea flux by wall-found ureolytic bacteria.

Ammonia↗
PubMed1979

Colonization of a portion of the bovine tongue by unusual filamentous bacteria.

Tongue samples from cattle on varied diets and ranging in age from 2 months to adult were studied by transmission and scanning electron microscopy to observe the in situ distribution and adhesion patterns of two readily identifiable genera of filamentous bacterial. The two, both members of the Simonsiellaceae, adhere to the epithelium by means of fibers which are produced on one side of the bacterial filaments and subsequently display a sidedness in their manner of adhesion to epithelial surfaces. Other bacterial populations found on the tongue were normally members of chains and seldom present as single cells. This suggests that filamentous or chain-forming bacteria may have a selective advantage over single bacteria in their ability to colonize and remain attached to the epithelium of the tongue.

Animals↗