Bacterial population

Resistance to antimicrobial agents is of concern as it is well known that bacterial resistance to antibiotics can develop. Many bacteria already derive some nonspecific resistance to biocides through morphological features such as thek cell wall. Bacterial populations present as part of a biofilm have achieved additional resistance owkig to the more complex and thicker nature of the biofilm. A system contaminated with a biofilm population can requke several orders of magnitude more chlorine to achieve control than unassociated bacteria of the same species. A second type of resistance is attributed to chemical deactivation of the biocide. This deactivation resistance to the strong oxidising biocides probably will not occur (27). 

Owing to the ubiquitous natural occurrence of vitamin K and its production by intestinal bacteria, vitamin K deficiencies are rare. However, they can be caused by certain antibiotics (qv) coupled with a reduced dietary intake. Newborn infants who do not possess the necessary intestinal bacterial population are at danger for vitamin K deficiency. As a result, vitamin K injections are routinely given to the newborn. 

Resistance to Tetracyclines. The tetracyclines stiU provide inexpensive and effective treatment for several microbial infections, but the emergence of acquired resistance to this class of antibiotic has limited their clinical usehilness. Studies to define the molecular basis of resistance are underway so that derivatives having improved antibacterial spectra and less susceptibiUty to bacterial resistance may be developed. Tetracyclines are antibiotics of choice for relatively few human infections encountered in daily clinical practice (104), largely as a result of the emergence of acquired tetracycline-resistance among clinically important bacteria (88,105,106). Acquired resistance occurs when resistant strains emerge from previously sensitive bacterial populations by acquisition of resistance genes which usually reside in plasmids and/or transposons (88,106,107). Furthermore, resistance deterrninants contained in transposons spread to, and become estabUshed in, diverse bacterial species (106). 

In all antiseptic testing, it is recognized that skin and mucous membranes to which products ate appHed cannot be disinfected or sterilized but it is possible to significantly reduce the population of transient and resident pathogenic bacterial flora. AH in vivo test methods requite a deterrnination of the bacteria on the skin before and after treatment. Because of the normal variation in bacterial population of the skin of different people, a number of people must be tested in order to make a statistical analysis of the results. Different parts of the body are used for different tests. In aH of the tests the details of the protocol ate extremely important and must be strictly adhered to in order to obtain reproducible results. 

Bacterial Population Count. Commercially available test media following API specifications are available for field testing. The two test sera available for inoculation by sample solutions are ... 

The term aggressive is often used to imply some approximately quantitative estimate of the likelihood of corrosion and depends on measuring factors such as soil water (resistivity), pH, redox potential, salt concentrations and bacterial populations in order to establish criteria for the prediction of corrosion rates . Similar measurements for predicting corrosion... 

Because physiological deterioration is generally accompanied by an increase in bacterial population, as pointed out by Nielsen, Wolford, and Campbell (33), estimation of bacterial numbers might serve as the basis of a test for condition. Obviously, the plate count method is not adaptable because of the time limitations imposed. Direct microscopic count would be much more appropriate, especially if a positive field count were substituted for cell count as suggested by Wolford (39). 

An even simpler and perhaps more effective approach to the problem might be application of the resazurin test as applied in the milk industry for indirect estimation of bacterial population. Proctor and Greenlie (34) have suggested this application, and Wolford (38) has worked with it in a limited way. The test is based upon a color change involved in the reduction of the dye. The time required for reduction decreases with increase in bacterial numbers. Intensive investigation of this method and its application with respect to increasing its sensitivity, and correlation of reaction rates with bacterial population and quality characteristics of the product, might be of considerable value. 

Misleading interpretation might result if bacterial population estimation were applied to material held under refrigerated conditions. Under such conditions bacterial development is materially held in check, while physiological deterioration still continues to... 

Great care, skill and understanding are required to determine the state of a bacterial population whether growing, stationary or dying. 

Disinfectant. This term implies a substance with bactericidal action. Clearly, if an environment is to be made free fiom the ability to reinfect, its bacterial population must be destroyed. A detailed description of the meaning of the terms disinfectant and disinfection is provided in Chapter 10. 

In brief, the experimental technique is to create abacterial population in a close chamber, obtain a quantitative assessment of the viable airborne bacterial population by means of a suitable sampling device, submit the population to the disinfeetant action, whether ultraviolet tight, chemical vapour or aerosol, and then determine the airborne population at suitable intervals. 

The size of the bacterial population increased, although there was no effect on the second-order rates of transformation of a number of compounds including phenol, and the agrochemicals propyl 2,4-dichlorophenoxyacetate, methyl parathion and methoxychlor (Paris... 

Steen WC, TW Collette (1989) Microbial degradation of seven amides by suspended bacterial populations. Appl Environ Microbiol 55 2545-2549. 

In a few cases, proanthocyanidins act by inhibiting adhesion of bacterial populations to human cells. Clinical, epidemiological and mechanistic studies supported the role of cranberry in maintaining the health of the urinary tract thorough the prevention of adhesion of P-fimbriated uropathogenic E. coli... 

API Serial Dilution Method. The API serial dilution method is the most widely used method for the detection of microorganisms. Field test methods for estimating bacterial populations have been standardized. A standard method dealing with the dose-response (time-kill) testing for evaluating biocides has been established. Sampling methods are of special importance because effective sampling is essential to any successful analysis. 

Experiments have shown that bacterial cells may penetrate a solid porous medium with at least 140-mD permeability and that a bacterial population may be established in such a medium if suitable substrates are supplied. Enhanced... 

D. L. Jones, A. M. Prabowo, and L, V, Kochian, Kinetics of malate tran.sport and decomposition in acid soils and isolated bacterial populations the effect of microorganisms on root exudation of malate under A1 stress. Plant Soil /((2 239 (1996). 

H. J. Miller, G. Henken, and J. A. Van Veen. Variation and composition of bacterial populations in the rhizosphere of maize, wheat and grass cultivars, Canadian Journal of Microbiology 35 656 (1989). 

In conclusion, there are no absolute reasons in nature that would indicate a convenience for every species to embark on the risks and costs of a profound morphophysiological remodeling, at either the root or stem level, and to face the odds of hosting and feeding invasive bacterial populations. In many instances... 

A. M. Semenov, A. H. C. van Bruggen, and V. V. Zelenev, Moving waves of bacterial populations and total organic carbon along roots of wheat. Microh. Ecol. 37 116 (1999). 

Infections acquired from an external source are referred to as exogenous infections. These infections may occur as a result of human-to-human transmission, contact with exogenous bacterial populations in the environment, and animal contact. Resistant pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus spp. 

Antimicrobials also can be classified as possessing bactericidal or bacteriostatic activity in vitro. Bactericidal antibiotics generally kill at least 99.9% (3 log reduction) of a bacterial population, whereas bacteriostatic antibiotics possess antimicrobial activity but reduce bacterial load by less than 3 logs. Clinically, bactericidal antibiotics may be necessary to achieve success in infections such as endocarditis or meningitis. A full discussion of the application of antimicrobial pharmacodynamics is beyond the scope of this chapter, but excellent sources of information are available.15... 

Multidrug resistant tuberculosis (TB) The presence of at least 1% of Mycobacterium strains in a bacterial population or culture that are resistant to at least isoniazid and rifampin. 

Early rhizosphere establishment is demonstrated in 2-3 day-old wheat plants when there is a shift towards a population of amino acid requiring bacteria (19). Maximum activity and numbers of rhizosphere microorganisms correlated with maximum vegetative plant development (20-22). Once established, the rhizosphere remains qualitatively similar, but quantitatively increases from seedling stage to maturity (23). After maturity the bacterial population reverts to a population similar to that in non-rhizospheric soils. 

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