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Selective medium for Pseudomonas aeruginosa that uses 1,10-phenanthroline as the selective agent
1Department of Biology, Catholic University of America, Washington, D.C. 20064.
Abstract:
The MIC of 1,10-phenanthroline for 35 Pseudomonas aeruginosa strains was 128 micrograms/ml, whereas 32 micrograms or less per ml inhibited all other microorganisms tested. On the basis of these results, a selective agar for P. aeruginosa which contained 15 g of Trypticase soy broth (BBL Microbiology Systems), 15 g of agar, and 0.1 g of phenanthroline per liter was formulated. Forty-four P. aeruginosa strains yielded a mean efficiency of plating on this medium of 79% of the counts obtained on Trypticase soy agar, which was significantly higher than that obtained with pseudomonas isolation agar or Pseudosel agar. Pseudomonas cepacia, Pseudomonas fluorescens, Pseudomonas putida, Pseudomonas stutzeri, representatives of 13 other genera (including gram-negative rods, gram-positive rods, and cocci), and a yeast were not recovered within 48 h at 35 degrees C when approximately 10(7) CFU were plated on this medium. Only small colonies from one strain each of P. fluorescens and P. putida could be seen at 3 and 7 days, respectively, and they had an efficiency of plating of only less than 0.001%. When 10(7) CFU of either of these strains was plated with 10(2) CFU of P. aeruginosa, it did not interfere with the quantitative recovery of P. aeruginosa.
Insights
A new selective agar medium using 1,10-phenanthroline effectively isolates Pseudomonas aeruginosa. This medium inhibits other microorganisms, showing high efficiency for P. aeruginosa recovery and minimal interference from other bacteria.
Area of Science:
- Microbiology
- Bacteriology
Background:
- Pseudomonas aeruginosa is an opportunistic pathogen requiring specific isolation methods.
- Selective media are crucial for differentiating P. aeruginosa from other bacteria in clinical and environmental samples.
Purpose of the Study:
- To develop and evaluate a novel selective agar medium for the isolation of Pseudomonas aeruginosa.
- To determine the efficacy of 1,10-phenanthroline as a selective agent against other microorganisms.
Main Methods:
- Determined the minimum inhibitory concentration (MIC) of 1,10-phenanthroline for P. aeruginosa and other microorganisms.
- Formulated a selective agar medium containing Trypticase soy broth, agar, and 1,10-phenanthroline.
- Assessed the efficiency of plating (EOP) for P. aeruginosa on the new medium compared to existing media.
- Evaluated the selectivity of the medium against a panel of other bacterial species and a yeast.
Main Results:
- The MIC of 1,10-phenanthroline was 128 µg/ml for P. aeruginosa and ≤32 µg/ml for other tested microorganisms.
- The novel selective agar yielded a mean EOP of 79% for P. aeruginosa, significantly higher than other selective agars.
- The medium effectively inhibited the growth of numerous other bacterial genera and a yeast within 48 hours.
- Minimal growth of P. fluorescens and P. putida was observed, with negligible impact on P. aeruginosa recovery when co-plated.
Conclusions:
- A new selective agar medium containing 1,10-phenanthroline is highly effective for isolating Pseudomonas aeruginosa.
- This medium demonstrates superior selectivity and efficiency compared to existing Pseudomonas isolation media.
- The formulation allows for reliable quantitative recovery of P. aeruginosa without significant interference from other common microorganisms.
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