Inability of the API-20E system to speciate the fluorescent group of pseudomonads

One thousand randomly selected clinical isolates of the fluorescent group of Pseudomonas were speciated in parallel by the API-20E system and by a classic microbiologic 17-test battery. The classic battery identified the isolates as 993 Pseudomonas aeruginosa, five Pseudomonas putida, and two Pseudomonas fluorescens. To augment the P. putida and P. fluorescens data, 52 reference isolates were also tested in parallel. API-20E was found to identify 99% of P. aeruginosa as P. aeruginosa. However, the 59 P. putida and P. fluorescens isolates were not accurately identified and were designated 58% P. aeruginosa, 24% P. stutzeri, 16% ambiguous categories, and only 2% in agreement with the classic designation. These findings indicated that the API-20E system does not accurately identify the non-P. aeruginosa fluorescent pseudomonads and that errors in P. aeruginosa designations will increase as the percentages of P. putida and P. fluorescens increase in the population sample.