Modified Pseudomonas agar: new differential medium for the detection/enumeratio...

• Author(s): Ramalho, Rita ; Cunha, Joaquim ; Teixeira, Paula ; Gibbs, Paul A.
• Date: 2002
• Persistent ID: http://hdl.handle.net/10400.14/6807
• Origin: Veritati - Repositório Institucional da Universidade Católica Portuguesa
• Subject(s): Cetrimide; Mineral water; Nalidixic acid; P. aeruginosa; Pyocyanin
• Document Type: Article
• Language: English

Description

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 FeSO4. 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 FeSO4 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 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.