Staphylococcus vs. Streptococcus: Differences and Comparison Table
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Staphylococcus and Streptococcus are the two most common pathogenic Gram-positive cocci of medical importance. Telling them apart at the bench, and even at the Gram stain, has immediate clinical weight: a direct Gram stain from pus or blood showing cocci in clusters points toward anti-staphylococcal empiric coverage, while cocci in chains points toward a penicillin-based regimen, before culture results are available.
Figure: Streptococcus spp (S. pyogenes and S. pneumoniae)
These gram-positive cocci share traits such as Nonmotile, Non-sporing, and Facultative anaerobes.
Some of the major differences between Staphylococcus and Streptococcus are summarized in the table below.
| Characteristic | Staphylococcus | Streptococcus |
|---|---|---|
| Arrangement | Clusters (grape-like), occasionally pairs or short chains | Chains, or pairs (diplococci) for S. pneumoniae |
| Catalase | Positive | Negative |
| Coagulase | Variable (S. aureus positive, CoNS negative) | Not produced |
| Hemolysis | Variable, often beta (S. aureus) or none | Alpha, beta, or gamma, depending on species |
| Grouping system | None (species ID by coagulase, novobiocin, etc.) | Lancefield grouping (C-carbohydrate antigen) for beta-hemolytic species |
| Salt tolerance | Tolerates high salt, grows on Mannitol Salt Agar (7.5% NaCl) | Generally salt-intolerant |
| Common pathogenic species | S. aureus, S. epidermidis, S. saprophyticus | S. pyogenes, S. pneumoniae, S. agalactiae, viridans group |
| Representative diseases | Staphylococci mostly cause wound infections. Abscesses, wound infections, toxic shock syndrome, food poisoning, osteomyelitis, acute endocarditis, septic arthritis, surgical site infection, interstitial pneumonia, etc | Pathogenic species of streptococci cause pneumonia, meningitis, sore throat (pharyngitis), wound infection, necrotizing fasciitis, scarlet fever, rheumatic fever, acute post-streptococcal glomerulonephritis |
How to Remember
One line carries most of the weight: clusters make catalase, chains don't. Staphylococcus's grape clusters and its catalase-positive result go together, Streptococcus's chains and catalase-negative result go together.
A second important trait is salt tolerance: Staph likes salt, Strep doesn't, which is also the working principle behind Mannitol Salt Agar as a selective medium for Staphylococcus.
Where students get confused
- Enterococcus muddies the "Strep doesn't tolerate salt" rule. Enterococcus was historically classified as Group D Streptococcus and is still salt-tolerant (that's the basis of the salt tolerance test used for it), even though it's now its own genus. If a question mentions salt-tolerant Gram-positive cocci in chains, don't assume it can't be related to Streptococcus, historically it was.
- Catalase-negative alone doesn't mean Streptococcus. Enterococcus is catalase-negative too. Catalase separates Staphylococcus from everything else in this comparison, it doesn't finish the identification on its own.
- Hemolysis pattern is not genus-defining. Both genera include hemolytic and non-hemolytic species, S. aureus is usually beta-hemolytic but not always, and Streptococcus spans all three hemolysis types depending on species. Don't use hemolysis alone to call the genus.
References
- Causey, W. A. (1979). Staphylococcal and streptococcal infections of the skin. Primary Care, 6(1), 127-139.
- Kherabi, Y., Zeller, V., Kerroumi, Y., Meyssonnier, V., Heym, B., Lidove, O., & Marmor, S. (2022). Streptococcal and Staphylococcus aureus prosthetic joint infections: are they really different? BMC Infectious Diseases, 22(1), 555. https://doi.org/10.1186/s12879-022-07532-x
- Moreillon, P., Que, Y. A., & Bayer, A. S. (2002). Pathogenesis of streptococcal and staphylococcal endocarditis. Infectious Disease Clinics of North America, 16(2), 297-318. https://doi.org/10.1016/s0891-5520(01)00009-5
- Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock Biology of Microorganisms (15th ed.). Pearson.
- Forbes, S., Sahm, D. F., & Weissfeld, A. S. (2002). Bailey & Scott's Diagnostic Microbiology. Mosby. https://amzn.to/2WZxPHL
Frequently Asked Questions
Does a Gram stain alone tell you whether an infection is Staphylococcus or Streptococcus?
Does a Gram stain alone tell you whether an infection is Staphylococcus or Streptococcus?
Largely yes, for a first impression. Clusters point to Staphylococcus, chains point to Streptococcus, and this distinction is often used to guide empiric antibiotic choice before culture results return. Confirmation still relies on the catalase test.
Why is catalase the key test for separating Staphylococcus from Streptococcus?
Why is catalase the key test for separating Staphylococcus from Streptococcus?
Catalase positivity is consistent across Staphylococcus and negative across Streptococcus, making it a fast, reliable, single-step test that pairs directly with the morphology seen on Gram stain (clusters with catalase-positive, chains with catalase-negative).
Tankeshwar Acharya, MSc (Medical Microbiology)
Tankeshwar Acharya is an Assistant Professor in the Department of Microbiology at Patan Academy of Health Sciences (PAHS), Nepal, where he has been teaching and practicing clinical microbiology for over 14 years. He is the founder of Microbe Online, one of the leading free microbiology education resources on the web, covering bacteriology, mycology, parasitology, immunology, and clinical laboratory diagnostics written from direct experience in both the classroom and the diagnostic laboratory.
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