Determination Of Bacterial Numbers Research Articles

Effects of betaine, organic acids and inulin as single feed additives or in combination on bacterial populations in the gastrointestinal tract of weaned pigs

A study was carried out to investigate whether blends of betaine, organic acids and inulin may improve their efficacy to modulate intestinal bacterial populations in weaned pigs compared with the single application of these additives. Moreover, potential postprandial diurnal variations in ileal bacterial numbers were determined in piglets fed the control diet. Twenty-four piglets in two consecutive experiments received a wheat-barley-soybean meal control diet (Con) or the Con diet supplemented with betaine (BET; 0.2%), an organic acid blend (AC; 0.4%) or inulin (IN; 0.2%) as single additives or in combination. Ileal bacterial numbers of total bacteria, lactobacilli, bifidobacteria (p < 0.05) and enterobacteria (p < 0.10) showed a postprandial diurnal variation, thus spot sampling of ileal digesta for the determination of bacterial numbers may not be representative. There were only small effects of BET, AC and IN on ileal and faecal bacterial populations. BET + AC increased total ileal bacterial numbers compared to the Con and AC treatments. BET reduced lactobacilli numbers in faeces, whereas BET + IN increased ileal numbers of bifidobacteria compared to AC and IN. There is evidence that BET, AC, IN and their combinations may affect proliferation of beneficial bacterial populations, although this has to be confirmed in further studies.

Murine pulmonary infection with Listeria monocytogenes: differential susceptibility of BALB/c, C57BL/6 and DBA/2 mice

Murine listeriosis is a paradigm to understand host pathogen interactions. Airway infections with Listeria monocytogenes, although representing a serious problem in early onset neonatal listeriosis, has not been investigated in detail in animal models so far. Here, the susceptibility of BALB/c, DBA/2 and C57BL/6 mice towards an intratracheal (i.t.) infection with virulent L. monocytogenes EGDe and the attenuated variant L. monocytogenes EGD hlyW491A(pERL3-CMVGFP) is reported. The course of infection was characterized by determination of bacterial numbers in the organs and assessment of the health condition of the mice. The distribution and cellular localization of Listeria in the airways was assessed by immunocytochemistry and confocal and electron microscopy. The differential susceptibility of inbred mouse strains to airway infections with L. monocytogenes could be assigned to the major virulence factor listeriolysin O. Resistant C57BL/6 mice were not affected by the two listerial strains. In contrast, BALB/c and DBA/2 mice showed differential susceptibility towards L. monocytogenes EGDe and attenuated bacteria, with all the mice being killed by the wild-type bacteria but rarely by the variant that secretes a listeriolysin of only 10% activity of that of the wild-type toxin. Thus, listeriolysin is a decisive factor for differential susceptibility against Listeria. After i.t. application, bacteria were predominantly localized in the peribronchiolar space and invaded alveolar macrophages but rarely lung epithelial cells. Dissemination from the lung into the deep organs started almost immediately after application, although a pulmonary bacterial reservoir remained during the first 4 days.

Influence of resin monomers on growth of oral streptococci.

Ethyleneglycol dimethacrylate monomers have been previously reported to stimulate the growth of certain caries-associated bacteria on the basis of turbidity measurements. To elucidate the detail of this effect, we examined the influence of resin monomers on the growth of Streptococcus sobrinus and Streptococcus sanguis by determination of bacterial numbers (colony-forming units), morphological observation, and chemical analysis. Although the absorbance values in the stationary phase of bacterial suspension were increased in the presence of ethyleneglycol monomers, no significant differences were observed for bacterial numbers throughout the incubation period. Scanning electron microscopy observation revealed the formation of sparse vesicular material surrounding bacterial cells when incubated with ethyleneglycol monomers, and these products were proved to be resin polymers. The results demonstrate that the apparent biomass increase during incubation with ethyleneglycol monomers is due not to promotion of bacterial multiplication, but to the polymerization of resin monomers to form vesicular structures attached to cells.

THE EFFECT OF DECOMPOSITION OF VARIOUS CROP PLANTS ON THE METABOLIC ACTIVITY OF THE SOIL MICROFLORA

Studies were undertaken to determine the changes in the soil microflora during the decomposition of plant residues. The methods used include the determination of bacterial numbers, dehydrogenase activity, and oxygen uptake with selected substrates (ethanol, amino acids, organic acids). Tests were conducted at varying intervals during a 66-day experimental period. Maximum activity was observed in all supplemented soils during the early stages of decomposition (5–10 days) followed by a rapid decline. During the first 10 days a correlation was found between numbers of microorganisms and the respiratory activity (oxygen uptake) of the soils. Analysis of the data from this period indicated that the increased metabolic activity of the soil was due partially to a preferential stimulation of the organisms and not to the effects of increased numbers alone. Nutritional grouping of bacteria isolated from the flax supplemented soil at 0 and after 6 days of decomposition indicated a shift in the microbial equilibrium, towards a higher proportion of bacteria with relatively simple nutritional requirements.

Microbial Population in the Rhizosphere of Yellow Poplar Seedlings

Living and dead microorganisms such as fungi, bacteria, and actinomycetes exert a profound influence upon the genetical development of soil profiles. Indirectly, through physical, chemical and microbiological decomposition, they may also affect the growth of forest trees. Although the quantity, or numerical content of organisms in any given soil are only relative indices of forest soil fertility, they offer valuable clues to potential plant growth and other site factors. Lohnis and Fred (1923) concluded that a determination of bacterial numbers in the soil is worthless as an attempt in interpreting soil phenomena. Later investigators, Waksman (1927) and Waksman and Starkey (1931) have clearly shown that numerical counts are important as well as indicative, when used in conjunction. with other edaphic and climatic factors. Shipman (1947), on studies of soil organisms in both natural and planted forests, has demonstrated that forest site quality is indirectly related to soil organism populations. An intimate relationship was found between the num-ber of microbes in the surface layers and age of the site. While the qualitative distribution of soil microorganisms remains much the same, there are very marked differences in the quantitative relationships of any given soil, as shown by Waksman and Starkey (1931). Considerable work has been done concerning the abundance of microorganisms in the root zone of cultivated plants. Hiltner (1904) introduced the term to designate that portion of the soil which is influenced by the immediate plant root system, or soil adjacent or adhering to the roots. He found, as have others, Hoffman (1915), Rakitzkaia (1926), Smith (1928) and Starkey (1929), that the rhizosphere soil supported greater microbial activity than soil more distant from the roots. It has been shown by Smith (1928) that the maximum effect or activity of organisms on the roots of leguminous plants cccurs in an advanced stage of seedling development, particularly in the flowering stage. Others have presented evidence that different plants exert varying influences, on the activity of soil organisms. However, there is practically no information concerning the influence of higher plants, such as forest tree seedlings, on soil microorganisms in the seedling stage of plant development. The present study was carried out to investigate the quantitative distribution of certain classes of soil organisms which may be present on the root system of yellow poplar (Liriodendron tulipifera L.) seedlings. The objectives were 1) development of a technique whereby soil organisms can be simultaneously isolated from both the rhizosphere and soil distant from the

Quantitative Distribution, Forest Soil Microorganisms in a Yellow Poplar Plantation

Since living microbes such as fungi, bacteria, and actinomycetes exert a profound influence upon the genetical development of soil profiles, they also exert an indirect effect upon the growth of forest trees. This is accomplished by altering the physical, chemical, and microbiological characteristics of the soil profile. Although the quantity, or numbers of organisms in any given soil, are only relative indices of forest soil fertility, these quantitative counts may offer clues as to the effect of other site factors. Lohnis and Fred (1923) came to the conclusion that a determination of bacterial numbers in the soil is worthless as an attempt in interpreting soil phenomena. However, later investigators (Waksman, 1927; Waksman and Starkey, 1931) have clearly shown that studies oln the numbers of organisms are important as well as indicative, when used in conjunction with other edaphic and climatic factors. In comparing numbers of bacteria, no single variable such as season of the year can be considered alone without reference to moisture content, acidity, and other factors, as shown by Waksman (1927). Studies of soil organisms in both natural and planted forest stands by Shipman (1947) have demonstrated that forest site quality is indirectly related to soil organism populations. Soil, whether in a natural state or once in cultivation, cannot be considered uniform in its spatial distribution of soil microorganisms. While the qualitative distri-bution of soil organisms remains much the same, there are very marked differences in the quantitative relationships of a given soil area (Waksman and Starkey, 1931). It is important to study these numerical variations, as expressed by horizon differentiation, whether visible natural horizons are present or not. In evaluating existing forest sites for actual or potential growth, or in appraising the value of any land to produce a crop, one cannot ignore the soil inhabitants and their effect upon the final crop. This microbial effect may be direct, as in the case of soil pathogens, or it may be indirect by altering the physical and chemical characteristics of the crop substrate. A field and laboratory study was undertaken to determine the total numbers, horizonal distribution, and seasonal fluctuation of certain forest soil organisms under a combination of environmental factors.

Determination of bacterial numbers on tableware by means of direct plating.

Determination of bacterial numbers on tableware by means of direct plating.

Determination of Bacterial Numbers on Tableware by Means of Direct Plating

Determination of Bacterial Numbers on Tableware by Means of Direct Plating

The influence of the method of sampling on the accuracy of the determination of bacterial numbers in the soil

Tests were made to determine the influence of the sampling and the preparatory treatment of the samples on the counting of bacteria in the soil. These proved that the present methods are very inaccurate and give rise to considerable variance in parallel determinations, to the extent even of rendering the effect of a perfected counting procedure quite negligible.

Local Lesions in Tobacco Mosaic

1. Five Nicotiana species were found to develop necrotic lesions wherever virus of the common field type of tobacco mosaic successfully entered leaf tissues. These species were N. rustica, N. langsdorffii, N. sanderae, N. acuminata, and N. glutinosa. 2. The local lesions developing in N. rustica can be used to measure accurately the potency of tobacco mosaic virus. 3. The local lesions in N. glutinosa are exceptional in the rapidity of their development. They sometimes begin to appear thirty hours after inoculation. In four or five days they are well developed. Large numbers of them may be distinguished on a single plant. This allows comparisons to be made between virus samples, since the number of lesions developing depends on the virus concentration of the inoculum. 4. A standardized method for using N. glutinosa as a test plant for measuring the concentration of mosaic virus gives as rapid and as accurate results as the determination of bacterial numbers by plating methods.