P3-48 AFNOR Validation of RAPID’ P. aeruginosa: A Shorter Method for Detection and Enumeration of Pseudomonas aeruginosa in Bottled Water

Tuesday, July 28, 2015
Hall B (Oregon Convention Center)
Christophe Quiring , Bio-Rad Laboratories, Food Science Division , Marnes-la-Coquette , France
Jean-Francois Mouscadet , Bio-Rad Laboratories, Food Science Division , Marnes-la-Coquette , France
Nathalie Bernard
Daniele Sohier , Adria Expert Laboratory , Quimper , France
Claudie Ledoeuf
Introduction: The standardized ISO 16266 reference method for the detection and enumeration of P. aeruginosa involves the use of CN agar. The lack of specificity of this medium requires subsequent laborious confirmatory tests. The reference method is consequently costly and time-consuming. The use of selective chromogenic agar increases the ease of use. Results are based on color change enzymatic reaction without confirmation, reducing the time to results.

Purpose: RAPID’P.aeruginosa was developed to allow the direct enumeration (without confirmation) of Pseudomonas aeruginosa using the membrane filtration method for the testing of water for human consumption. The principle is based on the detection of an enzymatic activity typical of P. aeruginosa.  The selective mixture makes it possible to inhibit the majority of interfering flora in particular Pseudomonas non-aeruginosa. An evaluation based on NF VALIDATION rules and ISO 16140 standard was conducted using a short (24 h) incubation time.

Methods: The chromogenic medium was evaluated by a comparison study performed by ADRIA Développement according the ISO 16140 requirements in comparison to the ISO 16266 reference method.

Results: Inclusivity study carried out with 25 P. aeruginosa strains showed that 24 strains were detected within 22 h on the chromogenic medium while the incubation time for CN Agar was 48 h. Among the 24 strains belonging to non-P. aeruginosa, none was able to grow on the chromogenic medium while 11 strains grew on CN agar, with one confirmed false positive. Relative accuracy was performed with 21 bottled water samples spiked with different levels of P. aeruginosa. Results showed that numerations obtained with chromogenic medium were equivalent to those obtained with CN agar.

Significance: RAPID'P. aeruginosa proved to be an effective alternative method for the detection and enumeration of P. aeruginosa in bottled water. The high specificity of the medium decreases time-to-results and costs associated with confirmation steps.