Gram-Positive Bacterial Identification Algorithm
Summary Table of Key Tests
| Test | Key Differentiation |
|---|---|
| Catalase | Staphylococcus (+) vs. Streptococcus/Enterococcus (–) |
| Coagulase | S. aureus (+) vs. other Staphylococci (–) |
| Novobiocin | S. epidermidis (Sensitive) vs. S. saprophyticus (Resistant) |
| Hemolysis | α, β, γ patterns on blood agar |
| Optochin + bile | S. pneumoniae (Sensitive, soluble) vs. Viridans strep (Resistant, insoluble) |
| Bacitracin + PYR | Group A Strep (+/Sensitive) vs. Group B Strep (–/Resistant) |
| Growth in 6.5% NaCl | Enterococcus (+) vs. Non-enterococcus (–) |
Learning Objective:
By the end of this algorithm, you should be able to use simple lab tests (catalase, coagulase, hemolysis, antibiotic sensitivities, and salt tolerance) to differentiate between Gram-positive cocci, bacilli, and branching bacteria, and identify clinically relevant pathogens such as S. aureus, S. pneumoniae, S. pyogenes, Clostridium, Bacillus, Nocardia, and Actinomyces.
Activity:
You must be logged in to post a comment.