Microbiology Staining Techniques & Spore-Forming Bacteria

Question-and-answer flashcards covering staining techniques (acid-fast, negative, endospore), associated bacteria, diagnostic methods, and spore-related clinical issues.

What minimum exposure time did the lecturer recommend when using saccharin as a substitute stain?

At least two minutes, because saccharin does not adhere as well and needs longer contact.

What is the only primary stain that works for the acid-fast staining technique?

Carbol fuchsin.

To what cell-wall component does carbol fuchsin bind in acid-fast bacteria?

Mycolic acid.

Which two bacterial genera typically give an acid-fast reaction?

Mycobacterium and Nocardia.

Which Mycobacterium species causes Hansen’s disease (leprosy)?

Mycobacterium leprae.

Which Mycobacterium species historically caused roughly 25 % of all deaths prior to 1900?

Mycobacterium tuberculosis.

What two diagnostic steps make up the practical "gold standard" for confirming tuberculosis in most of the world?

A chest X-ray showing a peripheral lung nodule plus an acid-fast stain of a sputum slide.

Why is a negative stain used to visualize bacterial capsules or slime layers?

Capsules do not retain basic or neutral stains; staining the background leaves clear "halos" around the cells.

In a negative stain, what part of the slide actually takes up the dye?

The background, not the capsule.

Which bacterial surface structures are key to biofilm formation?

Capsules and slime layers.

Roughly how long can Klebsiella pneumoniae survive on a tabletop because of its capsule?

About one to two months.

What is the only primary stain capable of penetrating bacterial endospores?

Malachite green.

What additional step is required to drive malachite green into an endospore?

Heating the slide to expand the spore and allow dye entry.

After malachite green, which counterstain is applied in an endospore stain to color vegetative cells?

Safranin.

What colors should you observe in a correctly performed endospore stain?

Green spores and red (pink) mother/vegetative cells.

Which two bacterial genera are clinically significant spore formers, and how do they differ in oxygen requirement?

Bacillus (aerobic) and Clostridium (anaerobic).

Which Bacillus species is considered a continuing bioterror threat?

Bacillus anthracis.

Food poisoning linked to fried rice is commonly caused by which Bacillus species?

Bacillus cereus (referred to as "cerevis" in the lecture).

Name the four major Clostridium pathogens discussed.

Clostridium tetani (tetanus), C. botulinum (botulism), C. perfringens (gas gangrene), and C. difficile (C. diff).

Why are purple-topped phenolic wipes used in hospitals?

They are among the few disinfectants that reliably kill resilient C. difficile spores on surfaces.

What rescue therapy may be used for recurrent C. difficile infection when antibiotics fail?

Fecal microbiota transplant (including freeze-dried "poop pills").

How does C. difficile survive a course of broad-spectrum antibiotics to cause later disease?

It forms highly resistant spores that outlast the antibiotics and later germinate when competing gut flora are gone.