BLOOD CULTURE AND SUSCEPTIBILITY (ADULT)

A blood culture incubates a blood sample in nutrient-rich liquid medium to detect bacteria or yeast circulating in the bloodstream. In adults, two sets of cultures (each set = 1 aerobic + 1 anaerobic bottle, 8–10 mL per bottle from two separate venepuncture sites) are drawn before antibiotics are started. The bottles are placed in an automated incubator (e.g. BD BACTEC or BioMérieux BacT/Alert) which monitors CO₂ production continuously and signals positivity, often within 12–48 hours.

When a bottle flags positive, a Gram stain is done immediately and the organism is sub-cultured on solid media for species identification (often by MALDI-TOF mass spectrometry) and antibiotic susceptibility testing (AST). A full report with organism and sensitivity profile is usually ready by day 3–5.

Bloodstream infection (bacteraemia, fungaemia) is a medical emergency. Sepsis kills millions globally each year, including a heavy burden in Indian ICUs and inpatient wards. A positive blood culture confirms the organism, allows de-escalation from broad-spectrum empirical antibiotics to a targeted, narrower drug, reduces unnecessary antibiotic use (slowing resistance), and is the only way to truly individualise therapy.

For Indian patients, the rise of multi-drug-resistant Gram-negative organisms (ESBL-producing E. coli and Klebsiella, carbapenem-resistant Enterobacterales) and methicillin-resistant Staphylococcus aureus (MRSA) makes susceptibility testing essential. An untargeted antibiotic choice in a resistant organism can be fatal; a culture-driven choice saves lives.

Blood culture is usually collected when you are febrile or before any planned antibiotic is given. The skin over the venepuncture site is cleaned with chlorhexidine or 70% alcohol and allowed to dry — meticulous sterile technique prevents skin-flora contamination (the most common cause of false-positive cultures). 8–10 mL of blood is drawn into each culture bottle. Two sets from two different sites are standard.

Do not eat or drink in a way that masks symptoms. Tell the doctor about any antibiotic taken in the past 7 days, recent travel, indwelling catheters / lines, and recent dental work.