Multi-Locus Sequence Typing (MLST) is a method used in molecular biology to categorize and identify different types of bacteria. This technique examines specific DNA sequences within a bacterial genome to distinguish between closely related strains. It provides a standardized and portable way to characterize bacteria.
Understanding Multi-Locus Sequence Typing
MLST operates by directly measuring variations in the DNA sequences of a select set of “housekeeping genes.” These genes are fundamental for a bacterium’s basic cellular functions and are generally present in most bacteria, making them suitable targets for comparison. For each chosen housekeeping gene, different sequences found within a bacterial species are assigned as distinct “alleles.” An isolate’s “allelic profile” or “sequence type” (ST) is then determined by the combination of alleles it possesses across all the analyzed genes. For instance, if seven housekeeping genes are examined, an isolate might be characterized by a series of seven numbers, each corresponding to a specific allele at each gene locus.
The Science Behind MLST
The process of performing MLST begins with selecting specific housekeeping genes, typically around seven, that are known to be stable within a bacterial species but show enough variation between strains to allow for differentiation. These genes are usually internal fragments, approximately 450-500 base pairs long, which can be accurately sequenced. Once selected, these gene fragments are amplified using a technique called Polymerase Chain Reaction (PCR). After amplification, the DNA sequences of these gene fragments are determined using automated DNA sequencing. The obtained sequences are then compared to a publicly accessible database, which contains a collection of known alleles for each target gene. This comparison allows for the creation of a unique allelic profile or sequence type for each bacterial strain, providing a precise way to differentiate them.
MLST in Action: Tracking Pathogens
MLST finds application in public health and microbiology, particularly in tracking bacterial pathogens. It helps scientists investigate the spread of bacterial outbreaks.
By comparing the sequence types of bacteria isolated from different patients or environments, researchers can identify common sources of infection and understand transmission pathways.
This technique is also valuable for monitoring the evolution and spread of antibiotic resistance in bacterial populations. Changes in the allelic profiles over time can indicate how bacterial strains are adapting and spreading within a community or across geographical regions. Epidemiologists utilize MLST data to build comprehensive pictures of bacterial populations, aiding in the development of more effective control strategies for infectious diseases.
MLST’s Role in Modern Microbiology
MLST has established itself as a foundational method within modern microbiology due to its standardized and portable nature. The ability to exchange primer sequences and protocols electronically, coupled with central databases, allows for consistent and comparable bacterial typing across different laboratories globally. This standardization has been invaluable for international surveillance efforts and collaborative research projects aimed at understanding bacterial diversity and evolution. The technique provides a precise and reproducible way to characterize bacterial strains, offering insights into their epidemiology and evolutionary relationships. MLST thus serves as a robust tool for contributing to a broader understanding of bacterial ecology, disease patterns, and the global spread of microbial threats.