Lab & diagnostics study sheet
| Lab method | Classification | Lab and identification clues | High-yield clue | Associations |
|---|---|---|---|---|
| 16S rRNA sequencing | Molecular identification concept; Sequencing vocabulary | Conserved/variable region vocabulary; Database match concept; Useful in slow-growing or hard-to-identify bacteria discussions | Conserved regions anchor amplification; the variable (hypervariable) regions are what distinguish organisms in the database match. | Bacterial taxonomy; MALDI-TOF comparison; Molecular ID workflows as concepts |
| Acid-fast stain | Differential stain; Cell-wall concept | Ziehl-Neelsen vocabulary; Auramine-rhodamine vocabulary; Mycolic acid concept | Acid-fast positivity is the stain clue for mycolic-acid-rich organisms. | Mycobacterium tuberculosis; Nocardia partial acid-fast vocabulary; Cryptosporidium modified acid-fast concept |
| Antigen test concept | Immunoassay concept; Detection vocabulary | Target antigen vocabulary; Sensitivity/specificity concepts; Rapid-test term recognition | Antigen test looks for a pathogen component; antibody tests look for host response. | Respiratory virus testing; Cryptococcal antigen; Giardia/Cryptosporidium antigen terms |
| Bacitracin (A disk) test | Presumptive disk concept; Beta-hemolytic cocci; Zone-of-inhibition readout | A-disk zone = presumptive Group A (S. pyogenes); No zone = Group B and most others; Pairs with PYR for Group A confirmation; Read on blood agar | Group A strep (S. pyogenes) is bacitracin-sensitive (zone present); Group B strep (S. agalactiae) is bacitracin-resistant. | Group A vs Group B beta-hemolytic separation; Study pairing with PYR and CAMP tests; Beta-hemolysis workup vocabulary |
| Bile solubility test | Differential biochemical concept; Applied to alpha-hemolytic cocci; Reads colony/broth clearing | Bile salts activate pneumococcal autolysin (LytA); Positive = colony dissolves/broth clears; Pairs with optochin sensitivity for pneumococcus; Viridans streptococci are bile-insoluble | Bile-soluble alpha-hemolytic colonies point to Streptococcus pneumoniae, while viridans streptococci stay insoluble. | Separates S. pneumoniae from viridans group; Study pairing with capsule and Quellung vocabulary; Alpha-hemolysis identification context |
| Blood agar hemolysis | Differential media concept; Hemolysis vocabulary | Alpha/beta/gamma terms; Streptococcal grouping context; Pattern recognition without procedure steps | Beta means complete clearing; alpha means partial greenish change; gamma means no hemolysis in study tables. | Streptococcus pyogenes; Streptococcus pneumoniae; Streptococcus agalactiae |
Assembled from the free PetriKey reference. Every row is published in full on its own reference page, with that page's own sources. Educational study reference only - not medical advice, and not for diagnosis, treatment, dosing, specimen handling, or any clinical decision-making.