Paper I — 2019 July (Supplementary) (2010 Scheme) — Q5
4 min read
Paper I
2019 July (Supplementary) (2010 Scheme) · 40 marks · 120 min
Question
Transport media
Q52 marksShort Notes
Answer
Transport media preserve the viability of pathogens in a clinical specimen during transit from the point of collection to the laboratory, without allowing multiplication or overgrowth of contaminating/commensal organisms, while preventing fastidious/fragile pathogens from dying due to desiccation or unfavourable conditions before culture.
Key properties: non-nutritive (or minimally nutritive), buffered to maintain stable pH and osmolarity, and reduced in oxygen content where anaerobes need to be preserved.
Examples:
Cary-Blair medium — the most widely used general-purpose transport medium for enteric bacterial pathogens (Vibrio cholerae, Shigella, Salmonella) in stool specimens.
Stuart’s/Amies transport medium — semisolid, non-nutritive media for swabs (throat, wound, genital) intended for general bacterial culture including Neisseria gonorrhoeae; Amies medium additionally contains charcoal to absorb toxic/inhibitory substances.
Venkatraman-Ramakrishnan (VR) medium — an alkaline transport medium specifically for Vibrio cholerae.
Sach’s buffered glycerol saline — used for Salmonella/Shigella stool specimens (glycerol is toxic to Vibrio cholerae).
Viral transport medium (VTM) — contains antibiotics/antifungals to suppress bacterial/fungal contamination, used for viral culture/PCR.
Clinical importance: correct choice and prompt use of transport medium (with appropriate temperature control during transit) is essential for reliable culture-based diagnosis, particularly for fastidious/fragile organisms.
