Biochemical Information and Courses from MediaLab, Inc.
These are the MediaLab courses that cover Biochemical and links to relevant pages within the course.
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The growth observed on the anaerobic blood agar plate after 48 hours incubation (see upper image), revealed a spreading colony. The spreading nature of the colony is better observed in the lower image. No growth was observed on subcultures incubated aerobically indicating that this isolate is truly an anaerobe (although aerotolerance studies would be needed for confirmation). The spreading nature of the colony and the lack of hemolysis are highly suggestive of Clostridium septicum. However, biochemical confirmation is necessary.
|Clostridium septicum RapID ANA|
The definitive identification of C. septicum can be made using a profile of biochemical reactions, as is contained in the RapID ANA strip seen in the image. The upper set of tubules are reactions before addition of reagents; the bottom set of reactions after reagents are added. The upper set of letter codes is used to read the reactions before addition of reagents; the lower set of labels indicate the tests to read following addition of reagents. Of all the reactions included, only ONPG and NAG in the upper set are positive. The biotype number derived from this profile of reactions, 014000 codes for Clostridium septicum, thus confirming the identification.
Ladhani S. Joannou CL. Lochrie DP. Evans RW. Poston SM.: Clinical, microbial, and biochemical aspects of the exfoliative toxins causing staphylococcal scalded-skin syndrome. Clinical Microbiology Reviews. 12:224-242, 1999 The exfoliative (epidermolytic) toxins of Staphylococcus aureus are the causative agents of the staphylococcal scalded-skin syndrome (SSSS), a blistering skin disorder that predominantly affects children. Clinical features of SSSS vary along a spectrum, ranging from a few localized blisters to generalized exfoliation covering almost the entire body. The toxins act specifically at the zona granulosa of the epidermis to produce the characteristic exfoliation, although the mechanism by which this is achieved is still poorly understood. Despite the availability of antibiotics, SSSS carries a significant mortality rate, particularly among neonates with secondary complications of epidermal loss and among adults with underlying diseases.
|S. anginosus ("milleri") Biochemicals|
The combination of decarboxylation of arginine (red color in the 2nd tube from left compared to the yellow color of the control to its left), the hydrolysis of esculin (black pigment in the esculin agar tube) and the reduction of nitrates to nitrites (red color in last tube on the right) are biochemical characteristics confirmatory for S. anginosus ("milleri").
Although not performed that often, the following tests are useful in separating E. corrodens from other closely related members of the HACEK group: KIA showing an alk/alk reaction; Glucose fermentation (-); Reduction of nitrates to nitrites (+); Production of indole (-); Ornithine decarboxylase (+) The positive nitrate reduction reaction eliminates Cardiobacterium hominis, Kingella kingae and other Kingella species. The positive ornithine decarboxylase reaction eliminates Kingella denitrificans (which also denitrifies nitrate to nitrogen gas, a reaction negative for E. corrodens). Eikenella corrodens is asaccharolytic, whereas most other closely related species produce acid from one or more carbohydrates.
|Size and Number|
Although lipoproteins of a particular class are generally within a given size range, there are many biochemical processes that interact with lipoproteins to alter their size, density, and lipid composition. When low-density lipoprotein (LDL) becomes smaller and denser, it is more likely to interact with the arterial wall, leading to deposition of cholesterol and initiating or worsening atherosclerosis. Research has shown that high numbers of smaller, denser LDL are more atherogenic than larger, lighter LDL particles. Small, dense LDL particles are associated with more than a three-fold increase in the risk of coronary heart disease.
|Introduction to the Fundamentals of Coagulation, continued|
When a vessel wall is damaged, blood flow out of the vessel is arrested by way of a complex series of interrelated physiological and biochemical processes. There are a wide variety of factors that influence the effectiveness of hemostatic processes including the following: Type of, and degree of, vessel damageAbility of vasoconstriction to occurAvailability of platelets & their functionalityAvailability of clotting factors & their functionalityAbsence of inhibitors and anticoagulantsThe image on the right illustrates vessel size as related to time required for clotting to occur, amount of coagulation products used (platelets and clotting factors), and size of the corresponding bleed.
|Secondary Hemostasis: Fibrin Formation via the Coagulation Cascade|
The formation of fibrin involves three interconnected biochemical pathways; the intrinsic, extrinsic, and common pathways. These pathways allow for the interaction of coagulation factors via a finely tuned sequence of chemical processes, where the factors themselves control the activity of the pathway. Most coagulation factors are stimulated and activated by the preceding factor, hence the term, "coagulation cascade. Since factor activation requires the activation of a preceding factor, a deficiency in the functionality or availability of any factor would seriously impact the effectiveness of the coagulation process. Factor deficiencies do occur, however, and often lead to impaired vascular repair and depressed hemostatic activity. The image to the right shows a fibrin clot containing red cells (red) and platelets (blue). The fibrin strands, which are created through the process of secondary hemostasis via the coagulation cascade, are shown in yellow.
|Secondary Hemostasis: The Intrinsic Pathway|
Exposure to contact substances, such as collagen, can activate the intrinsic pathway. The exposed collagen is the location where a complex forms between:High molecular weight kininogen (HMWK)Prekallikrein (also known as Fletcher Factor), which activates to kallikreinFactor XII (Hageman Factor) Together, this three-biochemical-complex, adhered to the collagen binding site, catalyzes the conversion of factor XII to its activated form, XIIa, thereby triggering the intrinsic pathway. The intrinsic pathway is circled in red in the image below.
|A definitive diagnosis of malaria can be made by:||View Page|
|Secondary Disorders of Iron Overload|
In addition to hereditary hemochromatosis (HH), there are other conditions of iron overload that must be considered in a differential diagnosis. Disorders such as sickle cell disease, thalassemia, sideroblastic anemia, congenital dyserythropoietic anemia, and liver disease may also cause iron overload. Transfusion-dependant patients and persons who abuse iron-containing vitamin supplements are also at risk. These conditions are usually described as secondary iron overload, in contrast to the primary iron overload of HH.Patient history, clinical signs and symptoms, biochemical and hematologic laboratory analyses, and possibly results of a liver biopsy may be needed to establish a diagnosis of a condition causing secondary iron overload. DNA tests for common HFE mutations are very likely the most important diagnostic tool for identifying HH as the cause of iron overload. In some patients, both secondary causes and HH may be contributing to iron overload. Differentiating the secondary causes of iron overload from HH is heavily dependent on the results of laboratory assays, but a complete discussion is beyond the scope of this course.
DNA tests for HFE mutations associated with hereditary hemochromatosis (HH) are available in some clinical laboratories and reference laboratories. Testing for the presence of the C282Y is essential, although most labs also test for H63D and S65C mutations. Molecular testing is most appropriate for confirmatory testing of symptomatic individuals with altered iron studies (increased TS and SF), in pre-symptomatic individuals (increased TS, normal SF and liver function tests), and in family members of individuals diagnosed with HH. The use of genetic tests alone for routine screening of asymptomatic persons is not recommended for several reasons. A positive test indicating the presence of HFE mutations does not guarantee that an individual will develop clinically significant iron overload or predict severity of symptoms. A negative result (no HFE mutations present) does not rule out a diagnosis of iron overload because of genetic heterogeneity. Compared to biochemical analyses for iron, molecular assays are expensive. Finally, molecular testing may result in the diagnosis of a genetic disease, thus opening up the possibility for discrimination in health insurance coverage. Using molecular methods, DNA is extracted from leukocytes in whole blood samples or from buccal cells and analyzed for specific HFE mutations using polymerase chain reaction (PCR) with melt curve analysis. Currently there are no FDA-cleared products for HFE testing, and testing laboratories are using "home brew" reagents. This situation is expected to change as manufacturers submit products for FDA approval.
|Round Cells in Semen|
Round cells in semen are of two types: immature sperm (germ cells) and white blood cells (WBCs). These cells can be differentiated by examining a stained smear at 1000X magnification. A more precise identification can be achieved by detecting peroxidase activity. The presence of immature germ cells could indicate testicular damage; increased numbers of WBCs may indicate inflammation of the accessory glands.
In previous exercises we have examined the formed elements of the urine sediment including casts, cells, crystals, and miscellaneous structures. If the urine sediment contains only a few elements, identification may be simple. However, a sediment may contain an overwhelming number of elements. If this is the case, there are biochemical tests to aid in differentiation of structures.