Modified Pseudomonas agar: new differential medium for the detection/enumeration of Pseudomonas aeruginosa in mineral
Rita Ramalho1, Joaquim Cunha, Paula Teixeira
1Escola Superior de Biotecnologia, Universidade Católica Portuguesa, Rua António Bernardino de Almeida, 4200-072, Porto, Portugal. rramalho@morango.esb.ucp.pt
Abstract:
Pseudomonas aeruginosa has been implicated as a foodborne and waterborne pathogen and is now considered a primary infectious agent. In the present study, the survival of P. aeruginosa inoculated in mineral water was evaluated by drop counts on Pseudomonas Agar Base (PAB), PAB with CN supplement X107, PAB with cetrimide, PAB with nalidixic acid, and these media with added FeSO(4). Initial counts, before starvation, were the same in all media tested. Following this period, P. aeruginosa became sensitive to PAB with added cetrimide. The addition of FeSO(4) did not improve the recovery of stressed P. aeruginosa but gave colonies a typical dark brown colour being easily differentiated from other species that can grow at 42 degrees C. The modified Pseudomonas agar medium was also tested with several P. aeruginosa strains, other species of Pseudomonas, and other genera. Only P. aeruginosa strains (pyocyanin positive) produced the typical colonies. Our results demonstrate that Pseudomonas agar with ferrous sulphate, used for the differentiation of P. aeruginosa colonies, and nalidixic acid, used as an inhibitor of Gram-positive bacteria, might be a useful medium for the detection of injured P. aeruginosa in mineral water.
Insights
This study evaluated methods for detecting Pseudomonas aeruginosa in mineral water. A modified Pseudomonas agar medium with ferrous sulphate and nalidixic acid showed promise for identifying stressed bacteria.
Area of Science:
- Microbiology
- Food Safety
- Water Quality
Background:
- Pseudomonas aeruginosa is a significant foodborne and waterborne pathogen.
- Effective detection methods are crucial for public health.
- Assessing bacterial survival under stress conditions is vital.
Purpose of the Study:
- To evaluate the efficacy of different culture media for detecting stressed Pseudomonas aeruginosa in mineral water.
- To identify a selective and differential medium for P. aeruginosa recovery.
Main Methods:
- Inoculating mineral water with P. aeruginosa.
- Using various Pseudomonas Agar Base (PAB) formulations, including supplements and ferrous sulphate (FeSO4).
- Employing drop counts for enumeration and assessing colony characteristics.
Main Results:
- P. aeruginosa became sensitive to cetrimide after starvation.
- Ferrous sulphate (FeSO4) aided in differentiating P. aeruginosa colonies by imparting a dark brown color.
- The modified medium with FeSO4 and nalidixic acid effectively detected injured P. aeruginosa.
Conclusions:
- Pseudomonas agar with ferrous sulphate and nalidixic acid is a potentially useful medium for detecting injured P. aeruginosa in mineral water.
- This medium aids in differentiating P. aeruginosa from other species.
- The findings contribute to improved water quality monitoring and food safety practices.
