Microbiology (GATE)

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

Aerotolerant anaerobes : Bacteria which have anaerobic growth, but continue in presence of oxygen

Correct answer.
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

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.

Mosses are bryophytes. They are not microbes.

Micromanipulator is used in single cell isolation technique for the isolation of microorganisms in pure culture. It is an equipment used to pick up a single cell and transferr to suitable medium.

Correct answer.
(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 sulfite agar-------inhibits gram-positive and most gram-negative bacteria, used to isolate Salmonella typhi.

Agar is more often used solidifying agent in culture media. It melts completely at the temperature of boiling water (97-100^oC) and solidifies when cooled to about 45^oC. It is chemically polysaccharide and is not attacked by bacteria and others microbes growing on it. Agar is obtained from seaweeds(Algae) called kelps.

Sterilization method is not a isolation method of microbes. A steam temperature of 121^oC is usually maintained for wet sterilization in autoclave at pressure 15 lbs/inch² (1.05 kg/sq.cm). Fifteen minutes of duration is sufficient for sterilization. Culture media are wet sterilized because they are either liquid or semi-solid gels containing water.

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

Gram Staining was developed by a Danish physician Hans Christian Gram in 1884. It helps to categorize bacteria in two groups, Gram Positive and Gram Negative. The smear of bacteria is prepared and stained with crystal violet. The smear is dipped in a mordant iodine solution which helps in strong adherence of the stain, and destaining is done with the help of ethanol or acetone.Gram Positive bacteria retain a purple colour of crystal violet, while Gram Negative bacteria lose purple colour. To stain Gram Negative bacteria, a counter stain safranin is used, so that they appear pinkish or reddish.

A steam temperature of 121^oC is usually maintained for wet sterilisation in autoclave at 15 lbs/inch². Culture media are wet sterilised because they are either liquid or semi-solid gels containing water.

Organisms which are strictly dependent on light for its energy source and on CO₂ for its carbon source are called obligate photoautotrophs.

Correct answer.
(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).

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