The genera that needs pyridoxal for growth is:

ESIC Nursing Officer -2019 (Shift -1)

Applied Microbiology & Infection control

Easy

Appeared in: ESIC Nursing Officer -2019 (Shift -1)

Explanation

Granulicatella species are classified as Nutritionally Variant Streptococci (NVS) due to their complex dietary needs.
These bacteria specifically require pyridoxal (a form of vitamin B6) or L-cysteine for their growth, which is not present in standard culture media.
This requirement leads to a phenomenon called 'satellitism', where the bacteria only grow near a source providing the essential nutrient, as depicted in the image.
Clinically, this makes them a cause of 'culture-negative' endocarditis, as they fail to grow in routine blood culture setups.

Option A: Aerococcus species are gram-positive cocci but do not have a specific requirement for pyridoxal for their growth. They can grow on standard laboratory media.
Option B: Enterococcus is a common inhabitant of the human gut and a frequent cause of nosocomial infections. It does not require pyridoxal for growth.
Option C: Pediococcus species are rarely pathogenic in humans and do not have a known requirement for pyridoxal for growth.

Visual 1: Diagram: A labeled diagram illustrating the satellite phenomenon, showing a central streak of a 'feeder' organism (e.g., Staphylococcus aureus) and the tiny 'satellite' colonies of the nutritionally-dependent organism (e.g., Granulicatella) growing only near the streak.
Visual 2: Flowchart: A diagnostic algorithm for 'culture-negative endocarditis', highlighting the step where special culture media (supplemented with pyridoxal and cysteine) should be requested for suspected NVS.
Visual 3: Infographic: A comparison table of different streptococcal groups (e.g., Viridans group, Group A, Group B, NVS), listing their key characteristics, common infections, and laboratory identification features.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Nutritional requirements of bacteria, specifically Nutritionally Variant Streptococci (NVS) as background academic context rather than a clinical decision trigger.
Understanding NVS is critical for diagnosing culture-negative infections, particularly infective endocarditis, which has high mortality if not treated appropriately.
Nurses should be aware that if a patient has persistent fever and signs of sepsis or endocarditis with negative routine blood cultures, they should communicate this to the medical team, as special laboratory investigations may be required.
What if? If a patient with suspected endocarditis has blood cultures that are negative after 48-72 hours, the nurse should anticipate the physician ordering special cultures for fastidious organisms like HACEK group bacteria and NVS (Granulicatella/Abiotrophia), which may involve holding blood in culture for an extended period or using supplemented media.

How to Approach the Question

First, identify the keywords in the question stem: 'genera', 'needs pyridoxal', and 'growth'.
The key term is 'pyridoxal'. This points towards a bacterium with a specific, unusual nutritional requirement.
Recall or deduce that bacteria with such special needs are often called 'fastidious' or 'nutritionally variant'.
Scan the options. Granulicatella is the classic example of a 'Nutritionally Variant Streptococcus' (NVS) that requires pyridoxal.
The other options (Aerococcus, Enterococcus, Pediococcus) are gram-positive cocci but are not known for this specific requirement and grow on standard media.
Therefore, select Granulicatella as the correct answer based on its unique metabolic dependency on pyridoxal.

Concept Tested & Keywords

Concept Tested: Nutritional requirements of bacteria, specifically Nutritionally Variant Streptococci (NVS)
Stem keywords: genera, pyridoxal, growth
Lead-in keywords: is

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