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Authors: D. Sue Katz , Marie Panec​

Citation: D. Sue Katz, Marie Panec. 2009. Plaque assay: illustrations of poor technique and plating problems.​

Publication Date: December 2009​

FIG. 1a. Plate illustrates viral host specificity when plated on restrictive host. Same viral inoculum. Figure 1a: Host Escherichia coli K12(l); Bubbles result from over-vigorous mixing and pouring of overlay. (D. Sue Katz, Rogers State University, Claremore, OK)

FIG. 1b. Plate illustrates viral host specificity when plated on restrictive host. Same viral inoculum. Figure 1b: Host Escherichia coli B (l); Bubbles result from over-vigorous mixing and pouring of overlay. (D. Sue Katz, Rogers State University, Claremore, OK)​

FIG. 2. Closeup of plaques. Unidentified virus. A bubble in the soft agar overlay is visible. Host: Escherichia coli B. (D. Sue Katz, Rogers State University, Claremore, OK)​

FIG. 3. Detail of plate. Plaques are visible, as are bubbles resulting from use of cold pipettes to pipet soft agar for the overlay.  Unidentified virus. Host: Escherichia coli B. (D. Sue Katz, Rogers State University, Claremore, OK)​

FIG. 4. Detail of plate in Figure 10. Plaques are 1 mm in diameter. Some bubbles resulting from pipetting soft agar with cold pipettes are seen. Unidentified virus. Host: Escherichia coli B. (D. Sue Katz, Rogers State University, Claremore, OK)​

FIG. 5. Illustrated on this plate are a mixture of viral plaques. One virus has formed clear plaques, the second virus has created a confluent lysis, with resistant bacteria visible as small colonies. A bubble in the overlay is also visible. Virus: unknown isolates from Winogradsky columns; Host: Escherichia coli B. (D. Sue Katz, Rogers State University, Claremore, OK)​

FIG. 6. Photo illustrates not only viral plaques but also some lumps resulting from pipetting soft agar with cold pipettes. Unidentified virus. Host: Escherichia coli B. (D. Sue Katz, Rogers State University, Claremore, OK)​

FIG. 7. Cold pipettes were used to aliquot the soft agar, resulting in bubbles and an incomplete overlay. Some plaques are visible. Host: Escherichia coli B. (D. Sue Katz, Rogers State University, Claremore, OK)​

FIG. 8. Cold pipettes were used to aliquot soft agar, resulting in a lumpy and bubbly overlay. Some plaques are visible.  Unidentified virus. Host: Escherichia coli B. (D. Sue Katz, Rogers State University, Claremore, OK)

FIG. 9. Closeup of plate where confluent lysis of susceptible host cells occurred; further incubation resulted in colony formation by resistant host cells. Unidentified virus. Host Escherichia coli B. (D. Sue Katz, Rogers State University, Claremore, OK)​

FIG. 10. Overlay is incomplete and plaques have been smeared as a result of using plates which are too fresh and which are too watery. Virus: fX174; Host: Escherichia coli K12(l). (Charly Hudson, Rogers State University, Rogers State University, Claremore, OK)​

FIG. 11. Several different sizes of plaques are seen in this plate. This can result from several reasons, including an impure stock or mutations. Overlay is incomplete, having hardened too quickly on an unwarmed base plate. Virus: fX174; Host: Escherichia coli K12(l). (Charly Hudson, Rogers State University, Rogers State University, Claremore, OK)

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