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Multiple Locus Variable-number Tandem Repeat Analysis (MLVA)

What is MLVA?

MLVA is another technique used by scientists to generate a DNA fingerprint for a bacterial isolate. Scientists usually perform MLVA after Pulsed-Field Gel Electrophoresis (PFGE) to find out more specific details about the type of bacteria that may be causing an outbreak.

How does MLVA work?

MLVA follows three main steps: polymerase chain reaction, sizing, and data analysis.

  • Polymerase chain reaction: Scientists begin MLVA with a process called polymerase chain reaction (PCR), which makes many copies of the specific DNA fragments that will help scientists identify the strain, or type, of bacteria that may be causing an outbreak.
  • Sizing: Scientists then determine the size of the bacteria’s DNA fragments using a process called high resolution capillary electrophoresis. The sizes of all of the bacteria’s DNA fragments are used to determine the bacteria’s MLVA type.
  • Data analysis: Scientists enter the information from the sizing process into special DNA analysis software and can compare different MLVA types to find out if the implicated clinical, food or environmental samples are similar to each other and the suspected outbreak source.

Advantages of MLVA

  • MLVA can connect suspected, fast-evolving bacterial strains to an outbreak when they might look the same using other methods of DNA fingerprinting, such as PFGE.
  • PulseNet USA uses MLVA as a complementary technique to PFGE, allowing scientists to see more detailed differences between bacteria that have similar PFGE patterns.

Limitations of MLVA

  • Requires a trained and skilled technician
  • Few standardized protocols available

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