Loeffler’s Serum Slope LSS

7 September, 2025

Introduction

Loeffler’s Serum Slope (LSS) is an enriched medium first developed by Friedrich Loeffler in 1887 for the cultivation of Corynebacterium diphtheriae.It contains serum (animal/human), nutrient broth, and glucose which support the rapid growth of fastidious organisms.The serum content provides growth factors and coagulates on heating, forming a slanted solid surface (slope) suitable for bacterial growth.

Media Type

Category: Enriched medium
Nature: Solid slope medium (due to coagulated serum proteins)
Purpose: Specially designed for cultivation and differentiation of Corynebacterium diphtheriae.

Composition & pH of Loeffler’s Serum Slope

Typical composition per liter:

Component	Function
Nutrient broth	Source of nitrogen, peptides, salts
Glucose (0.5–1%)	Energy source
Sterile serum (horse/rabbit)	Provides growth factors, coagulates to form slope
Sodium chloride (optional)	Maintains osmotic balance
Distilled water	Solvent

Final pH: 7.2 – 7.4 (at 25°C)

Sterilization

Serum media cannot be sterilized by autoclaving (heat will destroy serum proteins).
Instead, it is sterilized by fractional sterilization (inspissation method):
- Medium is heated at 80–85°C for 30–45 minutes on three consecutive days.
- This process kills vegetative bacteria while preserving serum proteins.

Preparation of Loeffler’s Serum Slope

Mix nutrient broth, glucose, and serum in proper proportions.
Dispense into test tubes.
Place tubes in a slanting position to create a slope.
Sterilize by inspissation at 80–85°C for 3 consecutive days.
Store at 2–8°C until use.

Uses of Loeffler’s Serum Slope

Isolation and cultivation of Corynebacterium diphtheriae
- Promotes rapid growth (colonies appear within 6–8 hours).
- Enhances metachromatic granule formation (observed by Albert’s stain).
Differentiation of diphtheria bacilli from other commensal Corynebacterium species.
Used for primary isolation from clinical specimens (throat swabs, nasal swabs).
Supports growth of some other fastidious organisms.

Limitations

Not suitable for organisms that require selective/differential conditions.
Serum-based medium → expensive and not always available.
Requires special inspissation equipment (not as simple as agar-based media).

Conclusion

Loeffler’s Serum Slope (LSS) remains a crucial medium in diagnostic microbiology, especially for diphtheria diagnosis. It allows rapid growth and demonstration of metachromatic granules, which are important in MBBS practical microbiology exams and laboratory practice.

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