Differential Diagnosis for Gram Positive Cocci in Chains

• Single most likely diagnosis
  • Streptococcus pyogenes: This bacterium is commonly found in chains and is a frequent cause of pharyngitis and skin infections, making it the most likely diagnosis based on the gram stain morphology.
• Other Likely diagnoses
  • Streptococcus agalactiae (Group B streptococcus): Also forms chains and is a common cause of infections in newborns and pregnant women.
  • Streptococcus dysgalactiae: Similar to S. pyogenes and S. agalactiae, it can form chains and cause various infections.
  • Enterococcus species: While typically found in pairs, some species can form short chains and are known for their role in urinary tract infections and endocarditis.
• Do Not Miss diagnoses
  • Streptococcus pneumoniae: Although it typically forms diplococci, some strains can appear in short chains. It's a critical pathogen to consider due to its potential to cause severe pneumonia and meningitis.
  • Streptococcus milleri group: This group includes several species that can form chains and are known for causing abscesses and infections in various parts of the body, including the brain and liver.
• Rare diagnoses
  • Abiotrophia species: These are fastidious gram-positive cocci that can appear in chains and are associated with endocarditis, particularly in patients with pre-existing heart conditions.
  • Gemella species: These bacteria can form chains and are rarely pathogenic but can cause endocarditis and other infections in immunocompromised individuals.