Peptostreptococcus species — mixed anaerobic infections (abscesses, aspiration pneumonia).
Samples to be collected: pus/aspirate from a deep abscess, tissue biopsy, blood (for anaerobic blood culture), and, for suspected C. difficile infection, stool. Superficial swabs from open wounds are generally unsuitable, given contamination by aerotolerant surface flora.
Sample collection process:
Aspiration is the preferred method for closed abscesses/collections — using a needle and syringe to aspirate pus directly from the lesion under aseptic technique, minimizing air exposure.
Tissue biopsy — a small piece of deep tissue is excised under aseptic conditions, providing a better sample than a surface swab for anaerobic culture.
Transport in anaerobic conditions — the sample must be transported promptly in an anaerobic transport medium/system (e.g., a sealed anaerobic transport vial, or the syringe itself with the needle capped, expelling all air) to prevent exposure to atmospheric oxygen, which rapidly kills obligate anaerobes.
Blood culture — collected using standard aseptic venepuncture technique, inoculated into a dedicated anaerobic blood culture bottle alongside the aerobic bottle.
Prompt transport to the laboratory — anaerobic specimens should reach the laboratory as quickly as possible (ideally within 30 minutes to a few hours), since prolonged exposure to air/delay significantly reduces recovery of viable anaerobic organisms.
Avoid swabs where possible — aspirated pus/tissue is markedly superior to a swab specimen for anaerobic recovery, given the greater sample volume and reduced air exposure during collection.
