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Unit Code 80349:
Bacterial Typing by Pulsed-Field Gel Electrophoresis (PFGE)

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Useful For

Bacterial typing is useful to investigate infection outbreaks by a

single species.

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 overinterpret or underinterpret.

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.

Reference Values

Reported as isolates from these sources are "indistinguishable" or

"different" by PFGE. Results will be faxed to the client.

Interpretation

Isolates which show identical DNA restriction fragment length

polymorphism (RFLP) patterns are considered to be closely

related.

Cautions

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 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.  

Special Instructions and Forms

• Infectious Material 

Clinical Reference

1.   Arbeit RD, Arthur M, Dunn R, et al:  Resolution of recent evolutionary

      divergence among Escherichia coli from related lineages:  the

      application of pulsed field electrophoresis to molecular

      epidemiology. J Infect Dis 1990;161:230-235

 

2.   Arbeit, RD:  Laboratory Procedures for the Epidemiologic

      Analysis of Microorganisms. In Manual of Clinical Microbiology,

      7th edition. Edited by PR Murray, American Society for Microbiology,

      Washington, DC. 1999 pp116-137

 

Key