General Bacteriology

• Staining of Chlamydia Species:
• In the Castaneda staining method (utilizing buffered methylene blue followed by safranin counterstain), the small, obligate intracellular elementary bodies of Chlamydia and Rickettsia stain intensely blue, contrasting against a reddish/pink cellular background.
• Comparison with Other Specialized Stains:
• Macchiavello's Stain: Elementary bodies stain bright red against a blue/green cytoplasmic background.
• Modified Ziehl-Neelsen (Stamp's) Stain: Elementary bodies stain red against a green (malachite green) or blue background.
• Gram Stain: Gram staining is ineffective for routine clinical detection of Chlamydia due to their minute size ($0.3\ \mu\text{m}$) and unique cell envelope lacking peptidoglycan.

Correct option: (3) Castaneda method of staining

• Etiology of 'New Duck Disease': New Duck Disease (infectious serositis / anatipestifer septicemia) is a contagious, devastating infection of young ducklings (1 to 8 weeks old) caused by Riemerella anatipestifer (formerly classified as Pasteurella anatipestifer).
• Clinical Signs & Pathology: Characterized clinically by ataxia, ocular and nasal discharge, sneezing, tremors ('head shaking'), and severe post-mortem lesions of fibrinous polyserositis (fibrinous pericarditis, perihepatitis, airsacculitis, and purulent meningitis).
• Taxonomic Reclassification: Originally placed in genus Pasteurella, the organism was transferred to the genus Riemerella within the family Flavobacteriaceae based on 16S rRNA sequencing and DNA-DNA hybridization.

Correct option: (2) Pasteurella anatipestifer