Bacteria Questions and Answers

Answer: D

Correct answer: all of the above

The spore is built in layers: an inner membrane round the core, a cortex of modified peptidoglycan between two membranes, and an outer keratin-like coat of protein - with an exosporium outside that in some species. Each layer contributes to its extraordinary resistance.

Answer: A

Correct answer: Ozeshki’s staining

Spores resist ordinary dyes, so they need a method that forces stain in - heat with a strong dye, then decolourisation, then a contrasting counterstain, so that the spore takes one colour and the vegetative cell another. That is what the spore stains of Ozeshki and of Schaeffer-Fulton do.

Answer: C

Correct answer: Loeffler’s technique

Volutin (metachromatic) granules are polyphosphate stores, and they stain a different colour from the rest of the cell with methylene blue - the metachromasia that gives them their name. Loeffler’s alkaline methylene blue is the classic method, and Neisser’s stain is used for the same purpose in Corynebacterium diphtheriae.

Answer: D

Correct answer: Morozov’s staining

A flagellum is far too thin to see by ordinary light microscopy, so it must first be thickened. Morozov’s silver impregnation deposits metal along it until it is visible - the same principle as the mordant-and-silver flagella stains generally.

Answer: B

Correct answer: Burri’s technique

A capsule takes up no dye, so it is shown by negative staining: India ink or nigrosin darkens the background while the cell body is counterstained, and the capsule appears as a clear halo between them. That is Burri’s method.

Answer: A

Correct answer: hanging drop technique

The hanging drop keeps the organisms alive and suspended in liquid under a cover slip over a cavity slide, so their true motility can be watched. Staining methods all begin by fixing - that is, killing - the cells, so they can never show movement.

Answer: D

Correct answer: All the above

Spirochaetes are too slender to be seen by ordinary bright-field microscopy of a stained film, so all three are used: dark-field microscopy on a fresh preparation, which shows them alive and moving; silver impregnation by Morozov, which thickens them; and the Giemsa and India ink methods.

Answer: D

Correct answer: All the above

Chlamydiae are non-motile, obligate intracellular parasites that cannot be grown on cell-free media - they must be cultured in living cells, because they cannot make their own ATP and depend on the host’s. That energy dependence is what defines them.

Answer: D

Correct answer: All the above

All three are true of mycoplasmas: they divide by binary fission, they are entirely without a cell wall, and being wall-less they are inherently resistant to penicillin and every other drug that acts on wall synthesis. They are treated with agents that act elsewhere, such as the macrolides and tetracyclines.

Answer: A

Correct answer: Eukaryotes

Fungi are eukaryotes: true nucleus, mitochondria, 80S ribosomes and a wall of chitin. Most are free-living saprophytes and grow perfectly well on cell-free media - which is exactly what distinguishes them from the obligate intracellular parasites.