Is Staphylococcus saprophyticus Gram-positive (Purple)?
Yes, Staphylococcus saprophyticus is definitively Gram-positive and stains purple on Gram stain. 1
Fundamental Staining Characteristics
S. saprophyticus retains the crystal violet stain and appears purple because it possesses a thick peptidoglycan cell wall characteristic of all Gram-positive bacteria. 1
The thick, relatively impermeable peptidoglycan wall of Gram-positive organisms like S. saprophyticus resists decolorization during the Gram staining process, maintaining the initial purple crystal violet stain rather than taking up the red counterstain. 1
Morphological Appearance on Gram Stain
S. saprophyticus appears as Gram-positive cocci arranged in grape-like clusters, which is the characteristic morphology of all staphylococcal species. 2
This clustering pattern distinguishes staphylococci from streptococci, which arrange in chains rather than clusters. 3
When evaluating respiratory or other clinical samples, trained laboratory personnel identify organisms with "Gram-positive suggestive of Staphylococcus" morphology based on this distinctive grape-like cluster arrangement. 2
Clinical Relevance
S. saprophyticus is a Gram-positive, coagulase-negative coccus that is the second most common cause of urinary tract infections in young, sexually active women after E. coli. 4, 5
Despite being Gram-positive, S. saprophyticus is an obligate human pathogen that specifically colonizes the urinary tract and can cause both cystitis and pyelonephritis. 5, 6
The Gram stain identification of Gram-positive cocci in clusters from clinical specimens has high specificity (95%) for identifying staphylococcal species, though sensitivity varies by clinical context. 2