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Ribotyping Method

For medical students2 min readUpdated 2026-10-10

Ribotyping is a modern molecular-genetic approach used for precise identification of microorganism species and monitoring of various bacterial strains. It is based on a detailed analysis of genetic variations in the arrangement of ribosomal RNA (rRNA) genes within the bacterial genome.

Genetic basisAnalysis of rRNA genes organized into operons

Main goalIdentification of bacterial species and strains

Genome featurerRNA operons are present in multiple copies

Mixed infectionsDetected via rRNA amplification

Genetic Basis of the Method

To understand how ribotyping works, it is essential to examine the organization of bacterial genetic material. The genes encoding rRNA are assembled into specific structures called operons.

A key property of the nucleotide sequence within these operons is its high degree of conservation. This means that these regions are extremely similar across all members of a single bacterial species. Furthermore, these operons do not exist as a single copy in the bacterial chromosome; they are always present in multiple copies.

Principle of Variability

If rRNA genes are so similar, how do we distinguish one species from another? Microorganism differentiation in ribotyping relies on three key features that are unique among different bacterial species:

Copy number of rRNA operons in the chromosome.
Topography (localization) of these copies within the genome.
Location of restriction sites—specific sites where enzymes cleave DNA. These sites may be located within the operon itself or in its flanking regions (adjacent neighboring areas).

Technique of Ribotyping

Today, the entire ribotyping process is fully automated, eliminating human error and accelerating turnaround time. The classical procedure consists of three main steps:

Restriction. Extracted bacterial DNA is treated with special enzymes called restriction endonucleases (restriction enzymes). Their role is to cut the long DNA molecule into short fragments at strictly defined positions (restriction sites).
Hybridization. The resulting DNA fragments undergo molecular hybridization with pre-prepared, labeled rRNA of the target species being investigated.
Profiling. Binding creates a unique fragment pattern (profile) that is characteristic exclusively of a specific bacterial species or even an individual strain.

Transcription-Mediated rRNA Amplification

This related method is used primarily when diagnosing mixed infections. Its core principle is the detection of specific bacterial rRNAs through artificial accumulation followed by hybridization.

The process takes place in automated analyzers and allows simultaneous detection of rRNAs from multiple bacterial species. The study proceeds in three stages:

Amplification. A large pool (multiple copies) of rRNA is synthesized using pre-extracted DNA as a template. The key enzyme at this stage is DNA-dependent RNA polymerase.
Hybridization. The abundantly accumulated rRNA is bound to complementary species-specific oligonucleotides (probes). To visualize the results, these probes are typically labeled with fluorophores or enzymes.
Detection. Hybridization results are read instrumentally using techniques such as densitometry or enzyme-linked immunosorbent assay (ELISA).

When diagnosing mixed infections, the amplified rRNA pool is simply divided into several separate samples. Each sample receives its own labeled oligonucleotide probe that is strictly specific to one particular pathogen.

Frequently asked questions

Which methods are used to separate DNA fragments after restriction prior to hybridization?

Separation of DNA fragments after restriction is typically carried out using gel electrophoresis.

Agarose gel electrophoresis is a method where fragment migration speed depends on size. Smaller fragments move faster and travel a greater distance, while larger ones move slower.
DNA molecules migrate from the negative pole (wells located at the top) toward the positive pole. Shorter fragments consequently end up further down the electropherogram.

What are the main differences between ribotyping and classical PCR?

The main differences lie in the principles of genetic material detection and the reaction steps.

Feature	Ribotyping Method	Classical PCR
Method basis	Analysis of genetic variations in rRNA gene arrangement	Amplification of specific DNA regions
Key steps	DNA digestion with restriction enzymes and hybridization with labeled rRNA	PCR amplification of specific targets

How is the unique fragment profile (pattern) physically formed and visualized during ribotyping?

The unique fragment profile in ribotyping is formed as follows:

extracted DNA is treated with restriction enzymes that cleave DNA into fragments;
the resulting fragments undergo molecular hybridization with labeled rRNA of the corresponding species;
this yields a unique fragment profile characteristic of a specific species or strain.

Automated systems handle the analytical workflow, matching profiles against reference databases.

What is the primary application of the ribotyping method?

The method is used for the precise identification of bacterial species and for monitoring various bacterial strains.

What are restriction sites?

These are specific sequences within a DNA molecule that are recognized and cleaved by specialized enzymes called restriction endonucleases.

Which enzyme is key during rRNA amplification?

The main enzyme during the amplification (accumulation) phase of the rRNA pool is DNA-dependent RNA polymerase.

How is the rRNA amplification method adapted for mixed infections?

The resulting rRNA pool is divided into several samples, and a unique labeled probe (oligonucleotide) specific for detecting a particular pathogen in the mixed infection is added to each.

Go deeper

Structure and function of prokaryotic rRNA operons
Mechanism of action of bacterial restriction enzymes
Principles of molecular hybridization
Instrumental detection: densitometry and ELISA
Application of fluorophores in molecular biology