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Slide Agglutination Test

Posted by Paul

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.

Serotypes

Posted by Paul

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.

Shigella

Posted by Paul

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.

Intestinal Pathogens

Posted by Paul

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.

Nikon Eclipse E200

Posted by Paul

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.

Bacterial Cell Wall

Posted by Paul

The bacterial cell wall contains a common and important component called peptidoglycan, which is only found in prokaryotes. Peptidoglycan is a polymer of alternating n-acetyl-glucosamine (NAG) and n-acetyl-muramic acid (NAM) which are linked by a covalent bond. Each NAM contains a chain of 4 amino acids. This amino acid chain crosslinks the adjacent polymers of amino sugars forming a lattice network around the exterior of the cell. It is this lattice that determines the shape of the cell (coccus, rod, or spiral). The lattice diversity results from a bridge being formed from different amino acids within the lattice. For example Staphylococcus may have the serine and glycine amino acid form a bridge as opposed to multimpl glycine residues. The cell wall of gram positive bacteria is made of up of 90% peptidoglycan. Most gram positive bacteria have teichoic acid in their cell wall as well. This is what creates the overall negative charge.

Ultraviolet Light

Posted by Paul

Ultraviolet light also referred to as UV light can be used as a germicidal agent to sterilize surfaces where sensitive microbiology techniques are being performed. UV light is nonionizing short wavelength radiation that falls between 4nm and 400nm in the visible spectrum. In general, the shorter the wavelength the more damaging it is to cells which makes UV light more damaging than visible light or infrared light. Most bacteria are killed by UV light. UV radiation at 260 nm is most damaging because at this wavelength DNA maximally absorbs UV light. When DNA absorbs UV light pyrimidine dimers form. A pyrimidine dimer is a covalent bond formed between two adjacent cytosine or thymine molecules in a DNA strand. These dimers distort the overall structure of the DNA strand and prevent DNA polymerase from moving past the dimer. Genes downstream from the dimer will not be transcribed and essential proteins will not be formed. The ability of the organism to function normally will be affected by the formation of one dimer.

Slime Mold

Posted by Paul

Slime molds are Eukaryotic, heterotrophic microorganisms that exist in cool, shady, and moist areas. They are often found on decaying logs, dead leaves, and other organic material. They ingest their food similar to an amoeba by phagocytosis. The vegetative cells lack cell walls however when fruiting bodies are formed, cell walls are present in these structures. Slime molds are in the division Gymnomycota in the Kingdom Myceteae. Slime molds have characteristics similar to protozoans and fungi and can be classified as either. The life cycle of the genus Physarum starts with the plasmodium. This is a multinucleate structure and moves over its food by flowing its cytoplasm similar to the way in which an amoeba moves. Most species feed on bacteria and other small organisms. The organism will change from its plasmoidal stage and form a sclerotia. The sclerotia is a hardened structure that forms when environmental conditions are not favorable. Sporangia can form under unfavorable conditions as well and they are fruiting structures. Sporangia can then give rise to pear shaped swarm cells.

Antibiotic Resistance

Posted by Paul

Antibiotic resistance is the ability of bacteria to develop immunity to antibiotics prescribed to treat infections. Antibiotic resistance is one of the world’s most pressing health problems and must be dealt with immediately. Antibiotics do not treat illnesses caused by viruses such as the flu, bronchitis, sore throats, and some ear infections and therefore should not be taken in such situations. The overprescription of antibiotics offers bacteria the opprotunity to produce future generations of bacteria that are not killed by antibiotics. Natural changes that occur in bacterial DNA may offer the bacteria an advantage when the microorganism encounters antibiotics. Antibiotics may also offer dangerous side effects. Antibiotics should only be prescribed for bacterial infections. MRSA or methicillin-resistant-staphylococcus aureus is a bacterium that has developed resistance to antibiotics such as penicillins and cephalosphorins. MRSA is prevalent in hospitals, prisons, and nursing homes where people have weakened immune systems. The amount of research dedicated to antibiotic resistance is disproportionate to the effect is has on our society and health system.

Norovirus

Posted by Paul

Noroviruses are viruses that are transmitted via fecally contaminated water and food, person to person contact, aerosolization of the virus, and contamination of surfaces. The virus flourishes in the winter because people spend less time inside and are closer to one another. Nororvirus outbreaks occur often in semi-closed communities such as long-term care facilities, hospitals, overnight camps, prisons, and cruises. Norovirus outbreaks occur throughout the year however over 80% of the outbreaks occur during November and April. When there are new strains of the virus new outbreaks tend to occur. Almost 67% of all norovirus outbreaks that occur in the U.S. occur in long-term care facilitites. These outbreaks are of great concern due to the large number of individuals with weakened immune systems. Outbreaks in this environment can last up to months. Norovirus is the leading cause of all food-borne illnesses in the United States. Nearly 50% of all cases in the U.S. from 2006 to 2011 were caused by the Norovirus. Cruise ships are also hot beds for norovirus activity. Due to the close living quarters, shared dining areas and rapid turnover of passengers the norovirus can pose a severe threat to one’s health. It is resistant to many common disinfectants which is why it is able to remain on surfaces throughout the ship.