Low Rates of Pseudomonas aeruginosa Misidentification in Isolates from Cystic Fibrosis Patients

Abstract

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.

Mucosal and systemic antibody responses to potentialPseudomonas aeruginosavaccine protein antigens in young children with cystic fibrosis following colonization and infection

“…Conventional laboratory bacteriology was used to identify P. aeruginosa from all clinical samples. 51 A group of otherwise healthy infants and young children who had not experienced an acute respiratory infection or received antibiotics in the previous two weeks and were undergoing bronchoscopy for congenital stridor served as a non-CF disease control group. None of the control children grew P. aeruginosa from their BAL or throat swab cultures.…”

Prevalence and species distribution of Achromobacter sp. cultured from cystic fibrosis patients attending the Aarhus centre in Denmark

“…Species-level identification of Achromobacter is difficult and isolates are frequently misidentified [7]. At present, the genus comprises 19 validly named species [8][9][10] and the clinical importance of different Achromobacter sp.…”

SharedPseudomonas aeruginosagenotypes are common in Australian cystic fibrosis centres

“…Ageadjusted pulmonary function prediction equations were used [17,18], and standard deviation z-scores were calculated using United States National Centre for Health Statistics and Centres for Disease Control and Preventionnormalised growth reference values for BMI. Sputum specimens were cultured by hospital diagnostic laboratories using standard techniques outlined previously [19]. When P. aeruginosa was identified, three colonies representing different morphotypes from each specimen (where possible) were selected by scientists independent of the study, isolated separately and transported to the research laboratory for storage at -80uC until further testing [19].…”

“…Sputum specimens were cultured by hospital diagnostic laboratories using standard techniques outlined previously [19]. When P. aeruginosa was identified, three colonies representing different morphotypes from each specimen (where possible) were selected by scientists independent of the study, isolated separately and transported to the research laboratory for storage at -80uC until further testing [19].…”