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A disease casued by microorganisms (such as bacteria, viruses) that enter the body and multiply in the tissues at the expesne of the host is said to be an infectious disease. Infectious diseases that are transmissible to other people are called communicable. The transfer of communicable infectious diseases between individuals can be accomplished by direct contact such as handshaking, kissing, and sexual contact. They can also be spread indirectly through food, water, objects and animals. Epidemiology is the study of how, when, where, what, and who are involved in the spread of disease in human populations. Epidemiologists determine the classification of the disease. If the number of newly reported cases in a given period of time in a specific area is excessive, an epidemic is in progress. If the disease spreads to one or more continents, a pandemic is in progress.
Between 1900 and 1940 a lot of research was performed to uncover the presence of other antigens in human red blood cells. In 1940, Landsteiner and Wiener reported that rabbit sera containing antibodies against the red blood cells of rhesus monkey would agglutinate the red blood cells of 5% of white humans. This antigen in humans which was first designated as the Rh factor, was found to exist as six antigens: C, c, D, d, E, and e. Of these six antigens, the D factor is responsible for the Rh-positive condition and is found in 85% of Whites, 94% of Blacks, and 99% of Asians. Typing blood for the rh factor can also be performed by both tube and slide methods but there are differences between the two techniques. The red blood cells must not be diluted in saline because they will not agglutinate and the test must be performed at 37 C for the tube test and 45 C for the slide test.
The procedure for blood typing was developed by Karl Landsteiner around 1900. He determined that human blood groups can be separated into four groups on the basis of two antigens that are present on the surface of red blood cells. These antigens are designated as A and B. The four groups are A, B, AB, and O. The last group, type O, which is characterized by the absence of A or B antigens, is the most common type in the U.S. (45% of the population). Type A is next in frequency at about 39%, type B is 12% and type AB 4%. Blood typing is performed with antisera containing high titers of anti-A and anti-B antibodies. The test can be performed in a tube where a drop of each kind of anti-serum is added to the separate samples of saline suspensions of blood cells.
A differential white blood cell count or differential WBC count can be used to determine which infectious disease is present in an individual. In 1883 Elie Metchnikoff puplished the phagocytic theory of immunity. He postulated that large cells in the tissue fluid and blood of animals were the first line of defense against foreign bodies. He stated that the larger cells were macrophages and the smaller ones were microphages. Neutrophils make up roughly 50-70% of the cells in blood, lymphocytes make up 20-30%, monocytes 2-6%, eosinophils 1-5% and basophils less than 1%. A normal white blood cell count is between 5,000 and 10,000 white blood cells per cubic millimeter. High white blood cell counts are referred to as leukocytosis. When counts fall below 5,000 leukopenia is said to exist.
Methicillin resistant Staphylococcus aureus is a bacterial infection caused by S. aureus that is extremely resistant to some antibiotics. Recently an elementary school in Chicago was shut down because several students were diagnosed with MRSA. S. aureus normally lives on the skin and in the nasal passages. The bacteria can cause infection if it enters through a cut, sore, or breathing tube. The infection can be minor such as a pimple or more serious involving the heart, lung or blood. Serious staph infections are more common in people with weak immune systems and people in hospitals and long-term care facilities. There are two types of MRSA infections: community associated and healthcare associated. Healthcare associated infections occur in people who have recently been hospitalized or had surgery in the past year. Community associated infections occur in healthy people who have shared items such as athletic equipment and razors and children in daycare facilities.
The slide agglutination test determines whether or not a specific protein exists within a species. Many manufacturers of reagents for slide agglutination tests utilize polystyrene latex particles as carriers for the antibody molecules. By conjugating reactive antibodies to these particles, an agglutination reaction results that occurs rapidly and is much easier to see than ordinary precipitin-type reactions that are used to demonstrate the presence of a soluble antigen. The test reagent is a suspension of yellow latex particles sensitized with antibodies for coagulase and protein A. Reagents are used to provide negative and positive controls. Disposable cards with eight black circles printed on them for performing the test. The black background of the card provides good contrast for the agglutination reaction that occurs.
Organisms of different species differ not only in their morphology and physiology but also in the characteristics that make up their molecular structure resulting in different serotypes. The proteins, polysaccharides, nucleic acids, and lipids define the molcular structure of an organism. Some of the macromolecules such as proteins, lipoproteins, and nucleoproteins can act as antigens because when these molecules are introduced into an animal, they cause the formation of antibodies. In order to produce antibodies, the substance must be foreign to the host organism. The antigenic structure of each species of bacteria is unique to that species similar to our fingerprints. These unique characteristics allow each species of bacteria to be differentiated from the next.
The Shigella are divided into four species: Shigella dysenteriae, Shigella boydii, Shigella Flexeri, and Shigella sonnei. Like the Salmonella, the four species are divided into a number of different serotypes. Serotypes are strains that have similar biochemical characteristics but differ in their antigenic composition. Various lines of evidence, including genetic analysis, suggests that the Shigella may be pathogenic variants or pathovars of Escherichia coli. Shigella affect only primate hosts and have a narrower range than E. coli. Shigella is of great medical importance due to its ability to cause gastroenteritis, bacillary dysentery, foodborne illness, and diarrhea in humans.
The intestinal pathogens of the most medical importance are the salmonella and shigella and pathogenic strains of Escherichia coli. They cause gastroenteritis, bacillary dysentery, foodborne illness, and diarrhea in humans. Right now the taxonomic differences of salmonella are being revised. In the first edition of Bergey’s Manual of Systematic Bacteriology, Salmonella is divided into two species, S. choleraesuis and S. bongori. S. choleraesuis is divided further into six subspecies based on different taxonomic and nucleic acid differences. If you base the classification system on antigenic differences the Salmonella can be divided into 2500 different serovars or serotypes, most of them belong to S. choleraesuis. A serovar is a strain that has similar biochemical characteristics but differ in their antigenic composition. It is important to identify serovars in order to determine the identity of the pathogen causing outbreaks of Salmonella infections.
The Nikon Eclipse E200 compound microscope offers superior optics and high quality construction. This is one of the most widely used microscopes in veterinary clinics and doctor’s offices. Nikon’s Chromatic abberation-free infinity (CFI60) system provides an expandable platform for more advanced microscopy techniques that involve the use of CCD cameras and laser microscopy systems. This optical system also offers crisp clear images allowing users to increase the efficiency with which they view their samples. Its durable construction and price point makes it a perfect fit for biology courses at the college level. College courses put a lot of wear and tear on microscopes forcing durability to be a high priority microscope requirement. The E200 also provides a cost effective solution for more advanced techniques such as darkfield, phase contrast, fluorescence and simple polarizing. The Nikon E200 has proven to be a solid microscope solution in a wide range of environments from college level courses, medical laboratories, doctor’s offices and research laboratories.