Low rates of Pseudomonas aeruginosa misidentification in isolates from cystic fibrosis patients

Timothy J. Kidd, Kay A. Ramsay, Honghua Hu, Peter T P Bye, Mark R. Elkins, Keith Grimwood, Colin Harbour, Guy B. Marks, Michael D. Nissen, Philip J. Robinson, Barbara R. Rose, Theo P. Sloots, Claire E. Wainwright, Scott C. Bell, Adam Jaffe, Tonia Douglas, Peter Cooper, Gerard Ryan, David Reid, Peter WarkBruce Whitehead, Hugh Greville, David Serisier, Carolyn Dakin, Iain Feather, Darrell Price, James Martin, John Wilson, David Armstrong

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42 Citations (Scopus)


Pseudomonas aeruginosa is an important cause of pulmonary infection in cystic fibrosis (CF). Its correct identification ensures effective patient management and infection control strategies. However, little is known about how often CF sputum isolates are falsely identified as P. aeruginosa. We used P. aeruginosa-specific duplex real-time PCR assays to determine if 2,267 P. aeruginosa sputum isolates from 561 CF patients were correctly identified by 17 Australian clinical microbiology laboratories. Misidentified isolates underwent further phenotypic tests, amplified rRNA gene restriction analysis, and partial 16S rRNA gene sequence analysis. Participating laboratories were surveyed on how they identified P. aeruginosa from CF sputum. Overall, 2,214 (97.7%) isolates from 531 (94.7%) CF patients were correctly identified as P. aeruginosa. Further testing with the API 20NE kit correctly identified only 34 (59%) of the misidentified isolates. Twelve (40%) patients had previously grown the misidentified species in their sputum. Achromobacter xylosoxidans (n = 21), Stenotrophomonas maltophilia (n = 15), and Inquilinus limosus (n = 4) were the species most commonly misidentified as P. aeruginosa. Overall, there were very low rates of P. aeruginosa misidentification among isolates from a broad cross section of Australian CF patients. Additional improvements are possible by undertaking a culture history review, noting colonial morphology, and performing stringent oxidase, DNase, and colistin susceptibility testing for all presumptive P. aeruginosa isolates. Isolates exhibiting atypical phenotypic features should be evaluated further by additional phenotypic or genotypic identification techniques.

Original languageEnglish
Pages (from-to)1503-1509
Number of pages7
JournalJournal of Clinical Microbiology
Issue number5
Publication statusPublished - May 2009
Externally publishedYes


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