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Updated: Jul 3, 2026
Aseptic Laboratory Techniques: Plating Methods
Published on: May 11, 2012
An evaluation of microbiologic contamination on phosphor plates in a dental school
Sajitha Menon Kalathingal1, Stephanie Moore, Soon Kwon
1Oral Health and Diagnostic Sciences, School of Dentistry, Medical College of Georgia, 1120 15th Street, Augusta, GA 30912-1241, USA. skalathingal@mail.mcg.edu
Objective:
The objective of this study was to determine if phosphor plates used in predoctoral clinics are microbiologically contaminated and to identify the source of contamination.
Study Design:
Forty-five of 300 phosphor plates (15%) were randomly selected for examination. The plates were pressed into individual blood agar plates, were incubated using standard techniques at 37 degrees C, and were monitored for 72 hours. The number, size, distribution, and variety of resulting colonies were noted. A representative of each type of colony was selected to be Gram stained using the standard technique.
Results:
Of the plates, 42.2% were uncontaminated, 57.8% yielded bacterial colonies, and 15.6% of those colonies demonstrated hemolytic growth. The hemolytic growth included combined alpha and beta hemolysis and beta only hemolysis. Six colonies were gram-positive rods and 7 were gram-positive cocci.
Conclusion:
Meticulous infection-control techniques are inevitable and continuous reinforcement and training for staff and students are mandatory. Periodic gas sterilization of phosphor plates may be necessary.
