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    ملخصات للميكروبيولوجي/Summary Of Microbiology

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    ملخصات للميكروبيولوجي/Summary Of Microbiology

    مُساهمة من طرف admin في السبت يوليو 09, 2011 9:29 am

    Laboratory Techniques in Microbiology
    A number of techniques are routine in microbiology laboratories that enable microorganisms to be cultured, examined and identified.


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    An indispensable tool in any microbiology
    laboratory is the inoculating loop. The loop is a piece of wire that is
    looped at one end. By heating up the loop in an open flame, the loop
    can be sterilized before and after working with bacteria. Thus, contamination of the bacterial sample is minimized. The inoculating loop is part of what is known as aseptic (or sterile) technique.


    Another staple piece of equipment is called a petri plate. A petri
    plate is a sterile plastic dish with a lid that is used as a receptacle
    for solid growth media.


    In order to diagnose an infection or to conduct research using a
    microorganism, it is necessary to obtain the organism in a pure culture. The streak plate technique is useful in this regard. A sample of the bacterial population is added
    to one small region of the growth medium in a petri plate and spread in
    a back and forth motion across a sector of the plate using a sterile
    inoculating loop. The loop is sterilized again and used to drag a small
    portion of the culture across another sector of the plate. This acts to
    dilute the culture. Several more repeats yield individual colonies. A colony can be sampled and streaked onto another plate to ensure that a pure culture is obtained.


    Dilutions of bacteria can be added to a petri plate and warm growth medium added to the aliquot of culture. When the medium hardens, the bacteria grow inside of the agar.
    This is known as the pour plate technique, and is often used to
    determine the number of bacteria in a sample. Dilution of the original
    culture of bacteria is often necessary to reach a countable level.


    Bacterial numbers can also be determined by the number of tubes of media that support growth in a series of dilutions of the culture. The pattern of growth is used to determine what is termed the most probable number of bacteria in the original sample.


    As a bacterial population increases, the medium becomes cloudier and
    less light is able to pass through the culture. The optical density of
    the culture increases. A relationship between the optical density and
    the number of living bacteria determined by the viable count can be
    established.


    The growth sources for microorganisms such as bacteria can be in a liquid form
    or the solid agar form. The composition of a particular medium depends
    on the task at hand. Bacteria are often capable of growth on a wide
    variety of media, except for those bacteria whose nutrient or
    environmental requirements are extremely restricted. So-called
    non-selective media are useful to obtain a culture. For example, in water quality
    monitoring, a non-selective medium is used to obtain a total
    enumeration of the sample (called a heterotrophic plate count). When it
    is desirable to obtain a specific bacterial species, a selective medium
    can be used. Selective media support the growth of one or a few
    bacterial types while excluding the growth of other bacteria. For
    example, the growth of the bacterial genera Salmonella and Shigella are selectively encouraged by the use of Salmonella-Shigella agar. Many selective media exist.


    Liquid cultures of bacteria can be nonspecific or can use defined
    media. A batch culture is essentially a stopped flask that is about one
    third full of the culture. The culture is shaken to encourage the
    diffusion of oxygen from the overlying air into the liquid. Growth occurs until the nutrients are exhausted. Liquid cultures can be kept growing indefinitely by adding
    fresh medium and removed spent culture at controlled rates (a
    chemostat) or at rates that keep the optical density of the culture
    constant (a turbidostat). In a chemostat, the rate at which the bacteria
    grow depends on the rate at which the critical nutrient is added.


    Living bacteria can also be detected by direct observation using a light microscope,
    especially if the bacteria are capable of the directed movement that is
    termed motility. Also, living microorganisms are capable of being
    stained in certain distinctive ways by what are termed vital stains.
    Stains can also be used to highlight certain structures of bacteria, and
    even to distinguish certain bacteria from others. One example is the
    Gram's stain, which classifies bacteria into two camps, Gram positive
    and Gram negative. Another example is the Ziehl-Neelsen stain, which
    preferentially stains the cell wall of a type of bacteria called
    Mycobacteria.


    Techniques also help detect the presence of bacteria that have become
    altered in their structure or genetic composition. The technique of
    replica plating relies on the adhesion
    of microbes to the support and the transfer of the microbes to a series
    of growth media. The technique is analogous to the making of
    photocopies of an original document. The various media can be tailored
    to detect a bacteria that can grow in the presence of a factor, such as
    an antibiotic, that the bacteria from the original growth culture cannot tolerate.


    Various biochemical tests are utilized in a microbiology laboratory.
    The ability of a microbe to utilize a particular compound and the nature
    of the compound that is produced are important in the classification of
    microorganisms, and the diagnosis of infections. For example, coliform
    bacteria were traditionally identified by a series of biochemical
    reactions that formed a presumptive-confirmed-completed triad of tests.
    Now, media have been devised that specifically support the growth of
    coliform bacteria, and Escherichia coli in particular.


    Various laboratory tests are conducted in animals to obtain an idea of the behavior of microorganisms in vivo.
    One such test is the lethal dose 50 (LD50), which measures the amount
    of an organism or its toxic components that will kill 50 percent of the
    test population. The lower the material necessary to achieve the LD50,
    the more potent is the disease component of organism.



    Medical Training and Careers in Microbiology
    The world of microbiology overlaps the world of medicine. As a
    result, trained microbiologists find a diversity of career paths and
    opportunity in medicine.


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    Research in medical microbiology can involve clinical or basic science. Clinical microbiology
    focuses on the microbiological basis of various diseases and how to
    alleviate the suffering caused by the infectious microorganism. Basic
    medical research is concerned more with the molecular events associated
    with infectious diseases or illnesses.


    Both medical training and microbiology contain many different areas
    of study. Medical microbiology is likewise an area of many specialties. A
    medical bacteriologist can study how bacteria can infect humans
    and cause disease, and how these disease processes can be dealt with. A
    medical mycologist can study pathogenic (disease-causing) fungi, molds and yeast to find out how they cause disease. A parasitologist is concerned with how parasitic microorganisms
    (those that require a host in order to live) cause disease. A medical
    virologist can study the diseases attributed to infection by a virus,
    such as the hemorrhagic fever caused by the Ebola virus.


    The paths to these varied disciplines of study are also varied. One
    route that a student can take to incorporate both research training and
    medical education is the combined M.D.-PhD. program. In several years of
    rigorous study, students become physician-scientists. Often, graduates
    develop a clinical practice combined with basic research. The experience
    gained at the bedside can provide research ideas. Conversely,
    laboratory techniques can be brought to bear on unraveling the basis of
    human disease. The M.D.-PhD. training exemplifies what is known as the
    transdisciplinary approach. Incorporating different approaches to an
    issue can suggest treatment or research strategies that might otherwise
    not be evident if an issue were addressed from only one perspective.


    The training for a career in
    the area of medicine and medical microbiology begins in high school.
    Courses in the sciences lay the foundation for the more in-depth
    training that will follow in university or technical institution. With
    undergraduate level training, career paths can include research assistant,
    providing key technical support to a research team, quality assurance
    in the food, industrial or environmental microbiology areas, and medical
    technology.


    Medical microbiology training at the undergraduate and graduate
    levels, in the absence of simultaneous medical training, can also lead
    to a career as a clinical microbiologist. Such scientists are employed
    in universities, hospitals and in the public sector. For example, the
    United Kingdom has an extensive Public Health Laboratory Service. The
    PHLS employs clinical microbiologists in reference laboratories, to
    develop or augment test methods, and as epidemiologists. The latter are involved
    in determining the underlying causes of disease outbreaks and in
    uncovering potential microbiological health threats. Training in medical
    microbiology can be at the Baccalaureate level, and in research that
    leads to a Masters or a Doctoral degree. The latter is usually undertaken if the aim is to do original and independent research, teach undergraduate and graduate students, or to assume an executive position.


    Medical technologists are involved in carrying out the myriad of
    microbiological tests that are performed on samples such as urine, blood
    and other body fluids to distinguish pathogenic microorganisms from the
    normal flora of the body. This can be very much akin to detective work, involving the testing of samples by various means to resolve he identity of an organism based on the various biochemical behaviors.
    Increasingly, such work is done in conjunction with automated
    equipment. Medical technologists must be skilled at scheduling tests
    efficiently, independently and as part of a team. Training as a medical technologist is typically at a community college or technical institution and usually requires two years.


    As in the other disciplines of medical microbiology, medical technology is a specialized field. Histopathology is the examination of body cells or tissues to detect or rule out disease. This speciality involves knowledge of light and electron microscopic examination
    of samples. Cytology is the study of cells for abnormalities that might
    be indicative of infection or other malady, such as cancer. Medical immunology
    studies the response of the host to infection. A medical immunologist
    is skilled at identifying those immune cells that active in combating an
    infection. Medical technology also encompasses the area of clinical biochemistry,
    where cells and body fluids are analyzed for the presence of components
    related to disease. Of course the study of microorganism involvement in
    disease requires medical technologists who are specialized
    microbiologists and virologists, as two examples.


    Medical microbiologists also can find a rewarding career path in
    industry. Specifically, the knowledge of the susceptibility or
    resistance of microorganisms to antimicrobial drugs is crucial to the
    development of new drugs. Work can be at the research and development
    level, in the manufacture of drugs, in the regulation and licensing of
    new antimicrobial agents, and even in the sale of drugs. For example,
    the sale of a product can be facilitated by the interaction of the sales
    associate and physician client on an equal footing in terms of
    knowledge of antimicrobial therapy or disease processes.


    Following the acquisition of a graduate or medical degree,
    specialization in a chosen area can involve years of post-graduate or
    medical residence. The road to a university lab or the operating room
    requires dedication and over a decade of intensive study.


    Careers in medical science and medical microbiology need not be
    focused at the patient bedside or at the lab bench. Increasingly, the
    medical and infectious disease fields are benefiting from the advice of consultants
    and those who are able to direct programs. Medical or microbiological
    training combined with experience or training in areas such as law or
    business administration present an attractive career combination.

      الوقت/التاريخ الآن هو الخميس ديسمبر 14, 2017 6:24 am