Abiotrophia / Granulicatella (variantes nutricionalmente deficientes)
Pleomorphic Gram-positive cocci in chains
Identification & Growth
Identification
- Do not grow on plain blood agar: require pyridoxal (vitamin B6) or cysteine
- Satellitism around a S. aureus streak
Growth Conditions
- Blood agar supplemented with 0.001% pyridoxal or a B6 disk, 5% CO₂
Clinical Significance
- Endocarditis with difficult-to-grow blood cultures
- Bacteremia in immunosuppressed patients
Intrinsic Resistance
- Aztreonam, colistin and nalidixic acid have no activity
Bench Alerts
- A positive Gram stain with no growth on subculture suggests this group
- Susceptibility testing requires supplemented medium (BrCAST/EUCAST: viridans streptococci criteria)
Clinical Notes
Clinical presentations
- Causes infective endocarditis associated with higher complication and treatment failure rates compared to typical viridans streptococci.
- Can cause occult bacteremia and abscesses in patients with an oral or dental portal of entry.
- Occasionally associated with ocular and joint infections.
Specimens and collection
- Blood cultures should be kept on extended incubation, as the organism is fastidious and slow-growing.
- Subculture on pyridoxal (factor V)-supplemented agar is required for growth on solid media.
- Valve tissue specimen should be considered in suspected endocarditis with negative blood cultures.
Epidemiology and at-risk populations
- Part of the human oral, gastrointestinal, and genitourinary microbiota.
- Patients with prior valvulopathy and recent dental procedures have elevated endocarditis risk.
- Frequently underdiagnosed as a cause of culture-negative endocarditis in laboratories lacking supplemented media.
Resistance and therapeutic implications
- Penicillin tolerance (bactericidal MIC much higher than inhibitory MIC) is described, justifying aminoglycoside combination therapy in endocarditis.
- Treatment failure and relapse rates are higher than with classic viridans streptococci.
- Vancomycin plus an aminoglycoside is an alternative in penicillin allergy or confirmed tolerance.
Bench and reporting notes
- Satellite growth around Staphylococcus aureus colonies on blood agar suggests pyridoxal dependence.
- MALDI-TOF with updated libraries improves identification compared to conventional biochemical methods.
- Report should alert the clinician to the need for combination therapy due to described antimicrobial tolerance.
Sources
- PubMed — Abiotrophia and Granulicatella review
- AHA/IDSA — Infective Endocarditis Guidelines
- EUCAST — Clinical breakpoints
Educational decision-support content. It does not replace laboratory validation, current guidelines or review by the responsible professional.
FAQ: Frequently Asked Questions
How to identify Abiotrophia / Granulicatella (variantes nutricionalmente deficientes) in the lab?
Abiotrophia / Granulicatella (variantes nutricionalmente deficientes) is identified through do not grow on plain blood agar: require pyridoxal (vitamin b6) or cysteine, satellitism around a s. aureus streak.
What are the intrinsic resistances of Abiotrophia / Granulicatella (variantes nutricionalmente deficientes)?
This organism is naturally resistant to aztreonam, colistin and nalidixic acid have no activity. These drugs should not be reported as susceptible.
Where is Abiotrophia / Granulicatella (variantes nutricionalmente deficientes) commonly found?
It is typically associated with endocarditis with difficult-to-grow blood cultures, bacteremia in immunosuppressed patients.
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