Principles and diagnostic application of the Hotis test:
(A) The Hotis test was developed by Hotis and Miller (1936) specifically to detect and differentiate the primary contagious mastitis pathogens, distinguishing Streptococcus agalactiae from Staphylococcus aureus in aseptically collected milk samples. The milk is mixed with bromocresol purple (0.5%) and incubated at 37 deg C for 24-48 hours. Streptococcus agalactiae ferments lactose, producing characteristic canary-yellow colonies or buttons along the side and bottom of the tube with an acid (yellow) column, whereas Staphylococcus aureus produces rust-colored or brown colonies/deposits with digest formation.
(B), (C), and (D) are not the primary differential target pair designed for the test.

Analysis of lysozyme distribution in milk and antibacterial susceptibility:
Statement (I) is incorrect: In bovine (cow) milk, lysozyme is present only in minuscule trace amounts (approximately $0.013\text{ to }0.07\text{ mg/100 ml}$), whereas human breast milk contains extraordinarily high concentrations of lysozyme (approximately $30\text{ to }40\text{ mg/100 ml}$, roughly 3,000 times higher than cow milk), conferring critical mucosal immunity to breastfed infants.
Statement (II) is correct: Lysozyme (muramidase) enzymatically hydrolyzes the $\beta(1\to 4)$ glycosidic bonds between N-acetylmuramic acid and N-acetylglucosamine in bacterial peptidoglycan. In Gram-positive bacteria, the thick peptidoglycan cell wall is directly exposed. In Gram-negative bacteria, the complex outer membrane rich in lipopolysaccharides (LPS) acts as a physical barrier preventing lysozyme from reaching the periplasmic peptidoglycan layer, rendering Gram-negative bacteria inherently far more resistant.

Characteristics of redox indicators in dairy microbiological testing:

• Methylene blue is a classic leucoform dye; when reduced by active bacterial dehydrogenase systems, the blue colored dye accepts hydrogen to form colorless leuco-methylene blue.
• Resazurin is also a leucoform indicator, sequentially reducing from blue to pink resorufin, and finally to colorless dihydroresorufin (leuco-resorufin).
• 2,3,5-Triphenyltetrazolium chloride (TTC / Tetrazolium) is a non-leucoform redox dye. Unlike leuco dyes which lose color upon reduction, colorless soluble tetrazolium salts are enzymatically reduced by cellular dehydrogenase systems of starter cultures (such as Streptococcus thermophilus) into a brightly colored, insoluble red precipitate called triphenylformazan. Inhibition of color development indicates the presence of antibiotic residues.
• Nigrosine is a negative structural staining dye, not a redox starter indicator.

Diagnostic criteria defining Lactic Acid Bacteria (LAB):
Lactic acid bacteria (encompassing genera such as Lactococcus, Streptococcus, Lactobacillus, Leuconostoc, and Pediococcus) are defined phylogenetically and physiologically by key universal traits:

• They are strictly Gram-positive (possessing a thick peptidoglycan cell wall with no outer membrane).
• They are catalase-negative (lacking heme-dependent catalase enzyme, relying on peroxidases or pseudocatalase to handle peroxides).
• They are non-spore-forming, fermentative rods or cocci that produce lactic acid as the major metabolic end-product of carbohydrate fermentation.