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Selective and differential medium for the primary isolation of members of the Proteeae
Abstract:
A new differential and selective medium for the isolation of members of the Proteeae, PIM (Proteeae isolation medium) agar, was developed and evaluated. The medium relies on the ability of all members of the Proteeae (with the exception of a very few Morganella morganii strains) to produce a dark brown pigment in medium containing DL-tryptophan. An additional differential property, tyrosine degradation, was also demonstrated by the medium. Members of the Proteeae appeared as dark brown colonies with a halo of clearing of fine tyrosine crystals when cultured on PIM agar. Occasional strains of Citrobacter sp. and Pseudomonas aeruginosa may degrade tyrosine, but none has the ability to produce dark brown pigmentation on PIM agar. Quantitative recovery studies showed that the addition of 5 mg of clindamycin per liter suppressed gram-positive bacteria without inhibiting any strains of the Proteeae. The addition of 100 mg of colistin per liter made the medium highly selective for strains of the Proteeae, but approximately 10% of the strains were not isolated, thus making this formulation unsuitable for general surveys of the occurrence of members of the Proteeae. PIM agar should aid the investigation of episodes of cross infection caused by members of the Proteeae and the isolation of the new species of the Proteeae recently described.
Insights
A new Proteeae isolation medium (PIM) agar differentiates bacteria by their ability to produce a dark brown pigment and degrade tyrosine. This selective medium aids in identifying Proteeae, crucial for infection control and new species discovery.
Area of Science:
- Microbiology
- Clinical Diagnostics
- Bacterial Isolation
Background:
- The Proteeae tribe, including genera like Proteus, Providencia, and Morganella, are significant in clinical settings.
- Accurate and efficient isolation of Proteeae is essential for diagnosing infections and epidemiological studies.
Purpose of the Study:
- To develop and evaluate a novel differential and selective medium, PIM agar, for the isolation of Proteeae.
- To assess the efficacy of PIM agar in differentiating Proteeae from other bacteria based on specific metabolic properties.
Main Methods:
- PIM agar utilizes DL-tryptophan for pigment production and tyrosine degradation for differentiation.
- Incorporation of clindamycin and colistin was tested to enhance selectivity and suppress contaminants.
- Quantitative recovery studies were performed to evaluate the medium's performance.
Main Results:
- PIM agar successfully differentiated Proteeae by their characteristic dark brown pigment production and tyrosine degradation, forming colonies with a clear halo.
- Clindamycin (5 mg/L) suppressed Gram-positive bacteria without affecting Proteeae.
- Colistin (100 mg/L) enhanced selectivity but led to the under-isolation of approximately 10% of Proteeae strains, deeming it unsuitable for broad surveys.
Conclusions:
- PIM agar is a valuable tool for the specific isolation and presumptive identification of Proteeae.
- The medium facilitates investigations into cross-infections and aids in the identification of newly described Proteeae species.
- Optimized formulations of PIM agar may be required for comprehensive epidemiological surveys.