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Test Code PFGE Bacterial Typing by Pulsed-Field Gel Electrophoresis (PFGE)

Biohazard Infectious

Reporting Name

Bacterial Typing

Useful For

Investigating infection outbreaks by a single bacterial species

Method Name

Pulsed-Field Gel Electrophoresis of DNA Fragments

Performing Laboratory

Mayo Medical Laboratories in Rochester

Specimen Type


Advisory Information

This test identifies bacterial strains, except for Staphylococcus aureusStaphylococcus spp., not S. aureus; Listeria spp., Bacillus spp., Enterococcus spp., Streptococcus spp., Lactobacillus spp., Legionella spp., Enterobacteriaceae, non-Enterobacteriaceae, and Clostridium perfringens.


For Staphylococcus aureus isolates, order BTWGS / Bacterial Typing by Whole Genome Sequencing.

Shipping Instructions

See Infectious Specimen Shipping Guidelines in Special Instructions for shipping information.

Necessary Information

Specimen source and organism identification are required for processing.

Specimen Required

Supplies: Infectious Container, Large (T146)

Container/Tube: Agar slant

Specimen Volume: Isolates on separate agar slants in pure culture

Collection Instructions:

1. Organism must be in pure culture, actively growing. Do not submit mixed cultures.

2. Place specimen in a large infectious container (T146) and label as an etiologic agent/infectious substance.

3. Place all pulsed-field gel electrophoresis (PFGE) specimens (all patients and/or sites to be compared) together in a large bag, and send in the same shipping container. This is necessary for comparison of isolates by this method.

Additional Information:

1. Each slant must be submitted under a separate order.

2. Original isolates should be saved at the client site if additional PFGE testing may be needed (eg, to compare to future outbreak isolates that may occur).

Specimen Stability Information

Specimen Type Temperature Time
Varies Ambient (preferred)

Reject Due To









Reference Values

Reported as isolates from these sources are "indistinguishable" or "different" by pulsed-field gel electrophoresis. Results will be faxed to the client.

Day(s) and Time(s) Performed

Monday through Friday; Continuously

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
PFGE Bacterial Typing In Process


Result ID Test Result Name Result LOINC Value
PFGE Bacterial Typing In Process

Analytic Time

5 days


The fact that 2 strains share the same pattern does not prove that they are epidemiologically related. Establishment of an epidemiologic relationship depends on the frequency with which the "indistinguishable" pattern is seen among epidemiologically unrelated isolates and correlation with clinical and epidemiological information.


Obviously, if common contact between 2 patients with strains with the same pulsed-field gel electrophoresis (PFGE) type can be established, the chances are greater that an epidemiologic link can be ascribed. Thus, the greatest power of PFGE typing is in showing strain dissimilarity, not in proving similarity or relatedness.

Method Description

Typing of bacterial isolates is accomplished by comparing the DNA restriction fragment length polymorphism (RFLP) patterns of large DNA fragments separated by pulsed-field gel electrophoresis (PFGE) of 2 or more bacterial isolates. Identical RFLP patterns indicate similarity of the isolates. The test is performed by isolating the DNA from the organism, cutting the DNA with a restriction enzyme which recognize 10 to 20 sites on the genome, and separating the fragments using PFGE. The size pattern of DNA fragments in the electrophoresis gel of different isolates is then compared.(Tenover FC, Arbeit RD, Goering RV, et al: Interpreting chromosomal DNA restriction patterns produced by pulsed-field gel electrophoresis: criteria for bacterial strain typing. J Clin Microbiol 1995;33:2233-2239)


Isolates which show identical DNA restriction fragment length polymorphism patterns are considered to be closely related.

Specimen Retention Time

1 month

Test Classification

This test uses a standard method. Its performance characteristics were determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

Clinical Information

Bacterial-typing techniques are useful for determining strain relatedness in the setting of nosocomial outbreaks or apparent outbreaks. Serial isolates obtained from the same patient can be typed to determine whether they are the same or different. Typing often allows the physician to discriminate between 2 species, recognize an outbreak, or identify the source of infection.


In the past, strain typing was accomplished by testing for different biochemical, phage, or antibiotic resistance patterns. Antibiograms are often unreliable because they are easy to over-interpret or under-interpret. Other strain-typing methods are often organism-specific and each requires a unique set of reagents and procedures. The availability of classical strain-typing techniques has been limited.


An excellent example of the power of the technique was in the analysis of a large number of clustered isolates of methicillin-resistant Staphylococcus aureus obtained from patients and staff at a Mayo Rochester hospital during September and October, 1992. Although the high frequency with which this organism was isolated suggested a nosocomial outbreak, molecular typing of the isolates showed: only 3 of the 14 were identical; the remaining isolates were most likely the result of a surge in the number of random isolates of this organism. Thus, the 14 isolates were not part of a nosocomial epidemic due to a single strain, and radical measures for control of a nosocomial outbreak were unnecessary.