Differential Diagnosis for Gram-Positive Cocci in Clusters
Single Most Likely Diagnosis
- Staphylococcus epidermidis: This is a common skin commensal that can cause infections, especially in patients with indwelling medical devices. It is a Gram-positive coccus that grows in clusters and is often coagulase-negative, distinguishing it from Staphylococcus aureus.
Other Likely Diagnoses
- Staphylococcus saprophyticus: Another coagulase-negative staphylococcus, S. saprophyticus is known to cause urinary tract infections, particularly in young, sexually active women. It is also a Gram-positive coccus that forms clusters.
- Staphylococcus lugdunensis: This species is less common than S. epidermidis but can cause more severe infections, including endocarditis and osteomyelitis. It is also a Gram-positive coccus in clusters.
Do Not Miss Diagnoses
- Streptococcus agalactiae (Group B Streptococcus): Although typically seen in chains rather than clusters, certain conditions or preparations might make S. agalactiae appear as cocci in clusters. It's a critical pathogen, especially in neonates and pregnant women.
- Enterococcus spp.: These bacteria can appear as cocci in pairs or short chains but might be mistaken for clusters. They are significant pathogens, particularly in urinary tract infections and endocarditis.
Rare Diagnoses
- Micrococcus spp.: These are environmental bacteria that can occasionally cause human infections. They are Gram-positive cocci that form clusters or tetrads but are less commonly pathogenic than staphylococci.
- Kocuria spp.: Formerly classified as Micrococcus, Kocuria species are also environmental bacteria that can rarely cause infections in humans. They appear as Gram-positive cocci in clusters.