Bacterial Classification and Staining Techniques

These flashcards cover key concepts and definitions related to bacterial classification and staining techniques, helping to reinforce understanding and prepare for exams.

Gram-positive bacteria

Characteristics include a thick peptidoglycan wall that retains crystal violet, appearing purple.

Gram-negative bacteria

Characteristics include a thin peptidoglycan wall and outer membrane, appearing pink due to safranin.

Decolorization effect

The effect where Gram-negative bacteria may appear Gram-positive due to insufficient decolorization.

Purpose of Gram stain

To provide rapid preliminary identification of bacteria using their morphology.

When is Gram stain most useful?

When analyzing specimens from sterile sites.

Staphylococcus morphology

Gram-positive cocci found in clusters.

Streptococcus morphology

Gram-positive cocci found in chains or pairs.

Streptococcus pneumoniae morphology

Gram-positive lancet-shaped diplococci.

Enterococcus morphology

Gram-positive cocci found in pairs or chains.

Neisseria morphology

Gram-negative, kidney-shaped diplococci.

Vibrio morphology

Gram-negative curved rods resembling commas.

Campylobacter morphology

Gram-negative S-shaped rods, resembling seagulls.

Yersinia pestis morphology

Gram-negative rods exhibiting bipolar staining.

Legionella Gram stain

Typically poorly visible when stained.

Enterics morphology

Gram-negative straight rods.

Pseudomonas morphology

Gram-negative thin rods.

Haemophilus morphology

Small, pleomorphic Gram-negative coccobacilli.

Corynebacterium morphology

Pleomorphic rods.

Listeria morphology

Small rods.

Bacillus morphology

Large rods.

Nocardia morphology

Branching filamentous structure.

Actinomyces morphology

Branching anaerobic filamentous structure.

Clostridium morphology

Anaerobic, spore-forming rods.

Acid-fast organisms

Organisms such as Mycobacteria that retain stains due to the presence of mycolic acids.

Primary stain in acid-fast staining

Carbol fuchsin.

Decolorizer in acid-fast staining

Acid-alcohol.

Counterstain in acid-fast staining

Methylene blue.

Acid-fast result of staining

Red organisms visible on a blue background.

Comparison of ZN vs Kinyoun

ZN method requires heat, while Kinyoun does not.

Auramine-rhodamine stain

A fluorescent stain for identifying acid-fast bacilli.

Acridine orange stain

Used to detect bacteria or yeast present in low concentrations.

Level 1 specimen processing

Immediate processing for blood, CSF, and fluids.

Level 2 specimen processing

Processing of unpreserved specimens such as urine, sputum, and stool.

Level 3 specimen processing

Involves quantitative specimens.

Level 4 specimen processing

Involves preserved specimens.

Reasons for specimen rejection

Reasons may include incompleteness, mismatch, leakage, or poor quality.

Why digest sputum?

To liquefy mucus.

Why decontaminate specimens?

To kill non-mycobacteria.

Agents used for decontamination

Common agents include NaOH, NALC, benzalkonium, and oxalic acid.

Which agent removes Pseudomonas?

Oxalic acid.

Nonselective media

Media that supports the growth of most organisms.

Example of nonselective media

Trypticase soy agar.