The microbiology section aims at studying yu ailments and diseases from the isolation of suspected causative organisms. The processes involved in the isolation of these organisms include; culturing, staining, microscopy and sensitivity tests. Samples collected for examination include; stool, blood, sputum, urine, vaginal swab, wound swab and wound biopsy. Bacterial Culturing and sensitivity
Cultures are carried out to isolate suspected organisms from a sample. There are different types of culture such as; blood culture, sputum culture, urine culture, wound swab and biopsy culture. Sputum culture: Required sputum should be collected after a deep cough and it is usually thick and purulent. It is important to ensure that the specimen is truly sputum and not saliva. Urine culture: since most urinary tract infections are caused by gram-negative bacilli, identification and sensitivity testing are of primary importance. Usually, identification of bacteria and determination of their sensitivity to specific antimicrobial drugs are done after the initial gram stain analysis. Most frequently, the identification of a specific organism must be accompanied by a sensitivity study. Also due to the changing patterns of resistance in other bacteria to antibacterial agents, sensitivity studies are essential. Clinically, the agar diffusion method is commonly used. The organism can be reported as being sensitive, intermediate or resistant to an antibiotic. Sensitivity depends on the growth characteristics of the organism and diffusion characteristics of the antibiotic. Some common antibiotics used include; GRAM POSITIVE
Bacterial morphology may be examined in two ways;
1. By observing the living, unstained organism, as in demonstrating bacterial motility. 2. By observing dead cells stained with dyes.
Living bacteria are almost colorless and do not present sufficient contrast with water in which they are suspended to be clearly visible. Staining the organisms makes them contrast in color with their surroundings, so they are readily visible. Thus the main advantage of staining is that it provides the contrast between microorganisms and their background, permitting differentiation among various morphological types.
Gram staining this staining method permits the classification of bacteria into two basic groups; Gram positive and Gram negative Bacteria Principle of gram staining
After staining with crystal violet and Lugol’s iodine, the morphology can be visualized. The blue stain depicts gram positive because the peptidoglycan in the cell wall of gram positive bacteria takes up the crystal violet and is resistant to decolorization with acetone, while a red stain depicts gram negative because the lipopolysaccharide on the cell wall of gram negative bacteria retains the color of the counter stain(safranin). Materials
crystal violet (primary stain), Lugol's iodine (mordant), Acetone (decolorizer), Safranin (counter stain), distilled water and clean glass slides. Procedure
Prepare a smear, allow to dry and fix with gentle heat.
Flood with crystal violet for thirty seconds and then rinse. Flood with Lugol’s iodine for thirty seconds and rinse.
Decolorize briskly with acetone under running water.
Counter stain with safranin for thirty seconds and rinse with water. Allow to dry and view slides under the microscope.
Acid-Fast Bacilli Ziehl-Neelsen Stain: This is a procedure used to stain a group of bacteria that does not readily take up stains. For example, Mycobacterium spp responsible for tuberculosis, hence this procedure is used in the diagnosis of tuberculosis. Principle
The lipid capsule of acid-fast bacilli takes up carbol fuschin and...
Please join StudyMode to read the full document