Safranin is used as secondary stain (counterstain) in Gram staining technique. Carbol fuchsin is sometimes substituted for safranin as counterstain, since it  more intensely stains anaerobic bacteria.

The Gram stain technique distinguishes between Gram-positive and Gram-negative bacteria by colouring these cells purple or pink. Gram positive bacteria stains purple due to the presence of a thick layer of peptidoglycan in their cell walls, which retains the crystal violet these cells during the decolouring process. Gram negative bacteria stains pink, which is attributed to a thinner peptidoglycan wall, which does not retain the crystal violet during the decolouring process.

Mannitol salt agar is both a selective and differential media used for the isolation of pathogenic Staphylococci from mixed cultures. MacConkey’s Agar is both a selective and differential media. It is selective for Gram-negative bacteria and can differentiate those bacteria that have the ability to ferment lactose.

Auramine-rhodamine stain is a histological technique used to visualize acid-fast bacilli using fluorescence microscopy. Kinyoun stain is a method of staining acid-fast microbes, specifically Mycobacterium and Nocardia. Ziehl-Neelsen stain is used to identify the acid-fast bacteria mainly Mycobacterium.

The reagents used in Ziehl–Neelsen staining method are carbol fuchsin (primary stain), acid alcohol, and methylene blue (counterstain). The Kinyoun staining method uses carbol fuchsin as a primary stain, followed by decolourization with an acid-alcohol solution and methylene blue as a counterstain.

Methyl red test detects production of acids formed during metabolism using mixed acid fermentation. The pH indicator Methyl Red is added to one tube and a red colour appears at pH's lower than 4.2, indicating a positive test (mixed acid fermentation is used). The solution remaining yellow (pH = 6.2 or above) indicates a negative test, meaning the butanediol fermentation is used.

Blood agar is both differential and enriched medium. The blood that is incorporated into this medium is an enrichment ingredient for the cultivation of fastidious organisms such as the Streptococcus species. Chocolate agar is enriched culture media commonly used for primary isolation of Haemophilus species from clinical specimens.

Proteus mirabilis and Proteus vulgaris can be differentiated by an indole test. Proteus vulgaris tests positive for indole test while Proteus mirabilis test negative for indole test.

Alcaligenes faecalis, Enterobacter aerogenes, Klebsiella pneumoniae: All are Gram-negative bacteria.

Catalase Test: The catalase test is done by placing a drop of hydrogen peroxide on a microscope slide. If the bacteria possess catalase, when a small amount of bacterial isolate is added to hydrogen peroxide, bubbles of oxygen are observed. If the mixture produces bubbles or froth, the organism is said to be 'catalase-positive' otherwise it is 'catalase-negative’. Enterobacter, Klebsiella, Nocardia, and Staphylococcus: All are catalase-positive bacteria.

Catalase test is used to detect the presence of the enzyme catalase in bacteria. Catalase serves to neutralize the bactericidal effects of hydrogen peroxide. It is a primary test used in the differentiation of Staphylococci and Streptococci. Staphylococcus aureus tests positive while Streptococcus pyogenes tests negative for catalase test.

Chocolate agar: Enriched media Phenylethyl alcohol agar: Selective media.

Hektoen Enteric Agar is a selective and differential agar for the isolation and cultivation of gram-negative enteric microorganisms, especially Salmonella and Shigella. MacConkey Agar is a selective and differential medium designed to isolate and differentiate Gram-negative enterics based on their ability to ferment lactose.

All are true statements. First TEM was built by Max Knoll and Ernst Ruska in 1931. TEMs are capable of imaging at a significantly higher resolution than light microscopes, owing to the small de Broglie wavelength of electrons. In TEM electrons are accelerated by an electric potential and focused by electrostatic and electromagnetic lenses onto the sample.

Voges–Proskauer test is used to detect acetoin in bacterial broth culture. The test is performed by adding alpha-naphthol and potassium hydroxide to the Voges-Proskauer broth,  which has been inoculated with bacteria. A cherry red colour indicates a positive result, while a yellow-brown color indicates a negative result. Both Enterobacter aerogenes and Klebsiella pneumoniae give positive Voges–Proskauer test.