Biphasic Medium in Microbiology: Introduction, Application, Merit, Demerits, and Keynotes
Biphasic Medium having bacterial growth
Introduction
Table of Contents
A biphasic medium is a culture system that combines both liquid (broth) and solid (agar) phases in the same container (usually a bottle or tube). It is designed to enhance microbial recovery by leveraging the advantages of both media types in one setup.
Fig. Biphasic Medium, having bacterial growthFig. Fungal growth (Aspergillus fumigatus) in a Biphasic medium
Applications
Blood culture systems (e.g., Castaneda’s medium for Brucella isolation)
If overused, it may allow overgrowth of contaminants in the broth phase
Requires careful aseptic handling to avoid back-contamination
Keynotes
Biphasic media are used for enhanced isolation of bacteria, especially in blood and sterile fluids.
Castaneda’s medium is a classic biphasic setup used for Brucella isolation.
Commonly used in manual blood culture systems.
Combines the liquid phase (supporting growth) and the solid phase (supporting colony isolation).
Important in slow-growing pathogens where subculture timing is crucial.
Fig. Aspergillus fumigatus growth in a blood culture bottle containing both liquid and solid agar phases-
Surface Growth: A fluffy to cottony white colony is observed initially on the agar slope, later turning blue-green to grayish-green as conidia mature. Submerged Growth: The liquid portion appears turbid or with floating fungal balls/mycelial clumps. Sometimes a mat of fungal growth forms at the interface of liquid and solid phases. Pigmentation: No distinct diffusible pigment is produced in the liquid phase, but the agar slope demonstrates typical fumigatus colony color after sufficient incubation. It was later phenotypically confirmed with the LPCB tease mount microscopy of this culture.
Fig. Aspergillus fumigatus in LPCB tease mount of culture microscopic image at a magnification of 1600X