Microbiology Methods and Techniques

Rickettsias, chlamydias (obligate intracellular pathogens) and Treponema pallidum do not grow in artificial media. Mycobacterium leprae is grown in armadillos because of its low temperature.

Oxyrase is a bacterial respiratory enzyme that can be put in media; it combines O₂ with H⁺ to remove O₂ by forming H₂O and turns the petri dish into a mini-anaerobic chamber. Anaerobic chambers with air locks are filled with inert gas.

Microbes can be preserved for long periods of time by deep-freezing or lyophilisation (freeze-drying). Deep freezing is done quickly, from -50° down to -95°C. Lyophilisation is a quick freeze in which a vacuum pump removes water in a process called sublimation.

Noble Agar is obtained by cutting agar gel into cubes and passing distilled water upward thru the tiny cubes to wash out salts and other small molecules, which diffuse out of the agar.

Aerotolerant anaerobes: Bacteria, which have anaerobic growth, but continues in the presence of oxygen.

Sodium Thioglycolate combines with dissolved O₂ to deplete O₂ in media.Oxyrase is a bacterial respiratory enzyme that can be put in media; it combines O₂ with H+ to remove O₂ by forming H₂O and turns the petri dish into a mini-anaerobic chamber.

The treatment of cells, generally with a mild surfactant, which dissolves cell membranes in order to allow larger dye molecules to enter inside the cell in cell staining techniques.

Bacteria have nearly the same refractive index as water, therefore, when they are observed under a microscope they are opaque or nearly invisible to the naked eye. So, different types of staining methods are used to make the cells and their internal structures more visible under the light microscope.

This is the true statement: Basic dye stains bacteria and Acidic dye stains background.

(a) Sabouraud glucose agar - inhibits most bacteria and is used to isolate fungi, (b) Blood agar - used to identify organisms that lyse red blood cells (Streptococcus pyogenes, )(c) Bismuth sulphite agar - inhibits gram-positive and most gram-negative bacteria, used to isolate Salmonella typhi.

Both option 3 and 4 are correct because fluorescent stains, type- 33258 and 33342, are Hoechst Stains and these are used to stain DNA in living cells.

Tissues which take up stains are called chromatic. Chromosomes were so named because of their ability to absorb a violet stain.

DAPI is a fluorescent nuclear stain, excited by ultraviolet light and showing strong blue fluorescence when bound to DNA . DAPI binds with A=T rich repeats of chromosomes. DAPI is also not visible with regular transmission microscopy. It may be used in living or fixed cells. DAPI-stained cells are especially appropriate for cell counting.

  (a) Psychrophiles (Cold Loving) can grow at 0° C, but optimum is about 15° C.  (b) Psychrotrophs can grow at 0° C also, but optimum is 20 - 30° C – important in food spoilage.  (c) Mesophiles(Moderate temperature loving) grow best at moderate around 37° C – many pathogens fall in this category.   (d) Thermophiles (Heat Loving) have a growth optimum at around 60° C.   (e) Hyperthermophiles have growth optima of 80° C or higher (archaea).

Correct answer: Levine's formulation is also known as Eosin Methylene Blue (EMB). EMB contains the following ingredients: peptone, Lactose, Dipotassium phosphate, Eosin Y (dye), Methylene blue (dye) and Agar.