In both conventional and rapid diagnostic workflows, what is the initial step after a positive blood culture?

• A. Subculture to agar
• B. Gram stain
• C. Rapid diagnostic test
• D. MALDI-TOF analysis

Answer: (B)

When a blood culture turns positive, the first test run in both conventional and rapid workflows is a Gram stain of material from the bottle. This quick smear gives immediate information about whether the organism is Gram-positive or Gram-negative and shows basic shape and arrangement (for example, cocci versus rods), which narrows the possibilities and guides the next steps. That early judgment helps clinicians pick initial empiric therapy and directs which culture plates to inoculate and what rapid tests or identification methods to apply next. After the Gram stain, the sample is typically subcultured to obtain isolated colonies for definitive identification and susceptibility testing, while rapid identification methods or MALDI-TOF are used once suitable material is available. The Gram stain is the essential frontline diagnostic step because it provides fast, actionable direction that all downstream workflows—whether traditional or rapid—rely on.