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Lecture 4

MCB 3020 Lecture 4: Microbiology lecture 4

3 Pages

Microbiology and Cell Science
Course Code
MCB 3020
Abdolkarim Asghari

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8/31/2017 Microbiology Lecture Four—Exam 1 • Basic dyes (positive) stick to surface of cells • Simple stain uses one stain to show morphology, size and arrangement • Types of dyes that may be used: o Positive staining: uses basic dye that binds to the specimen, CV o Negative Staining: uses acidic dye that binds to background, India ink • Examples of differential staining procedures: o Gram stain (most common) o Acid-fast stain (ex: for mycobacteria, Because need harsher stain) o Structural stains (ex: capsule, flagella, spores) • If kept gram color, then gram positive. If lost original color, gram negative. Purple/blue= positive, Pink= negative • Simple stains—everything same color, Crystal violet, methylene blue • Differential stains—acid fast, gram, endospore stain, India ink, Flagellar • Most important feature of stain (acid fast), is testing of TB • Gram stain shapes: o Rods (bacillus), coccus (circle), vibrio (shape of smile), coccobacillus (kinda square), spirochete (spiral shaped), Spirillum (wavy) • Bacillus and clostridium= has gram positive stain • Clostridium causes gangrene, anthrax Fluorescence Microscopy: • Used as a diagnosis of dangerous diseases o Dark-field microscopy—colors background and sees shadow of organism o Phase Contrast Microscopy—uses density of different components of cell. With different density, bends light differently • Antibody= protein that’s produced after finding an infection • Fluorescent dye binds to antibody; used as diagnostic tool • Electron microscopy (doesn’t use light source but uses electron beam as light source): o TEM— details of inside cell. Uses sharp tip to cut through cell o SEM—surface details • Confocal scanning laser microscopy: o Uses computer integration of images from many different focal planes (angles) to generate 3-D pictures. VERY SHARP IMAGES! o (REMEMBER) Fluorescent dye attached to antibodies are used in conjunction with laser light source to produce sharp images • Characterization of light and electron microscopy o Magnification o Resolution o Illumination source • Need electron microscopy to see viruses • Lower wave length= higher resolution (what clarity is) Recap • Simple stains—employs basic dye to impart a color to a cell. Easy way to increase the contrast between otherwise colorless cells and a transparent background • Differential stains—distinguishes one group of microorganisms from another • Gram stain—used to separate bacteria into two major groups, Gram-positive and Gram- negative. The staining characteristics of these groups reflect a fundamental difference in chemical structure of their cell walls. This by far most widely used staining procedure • Acid-fast stain—used to detect members of genus Mycobacterium in a specimen. Due to the lipid composition of their cell walls, these organisms do not readily take up stains • Special stains—stains specific structures inside or outside cell: o Capsule stain—because viscous capsule does not readily take up stains, it stands out against a stained background. This is an example of a negative skin stain o Endospore stain—S
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