129 Benefits of testing multiple isolates of Staphylococcus aureus isolated from the sputa of patients with cystic fibrosis

Abstract

Objective: To describe Dyella species associated with cystic fibrosis (CF). Methods: Phenotypic identification by VITEK-2; mass spectrometry; 16S rDNA sequencing; minimal inhibitory concentration by Etest® and categorisation as susceptible (S) or resistant (R) according to EUCAST interpretative criteria for Pseudomonas. Results: An oxidase-positive Gram-negative rod was isolated on Burkholderia cepacia selective agar in May 2009. Initially the bacterium was identified by VITEK-2 as Elizabethkingia meningoseptica, however subsequent 16S rRNA gene sequencing revealed it belonged to genus Dyella. Only one single human infection with Dyella (bacteremia in a hemodialysis patient) has been described previously. Dyella species was cultured from this patient in 5 of 11 sputum samples during 2010, and from 8 of 10 specimens in 2011, rendering the patient chronically infected when applying the “Leeds criteria” often used for Pseudomonas aeruginosa infection. An unusual antibiotic susceptibility pattern was observed: piperacillin–tazobactam, 3mg/L (S); meropenem, >32mg/L (R); fosfomycin, 256mg/L (R); ciprofloxacin, 3mg/L (R); moxifloxacin, 0.25mg/L (no breakpoint); tobramycin, 3mg/L (S); colistin, >256mg/L (R). A unique MALDI-TOF mass spectrum was displayed, and the strain is easily recognised by mass spectrometry after the generation of reference spectra. The patient experienced a steep decline in FEV1 (approx. 4%/year) for several years prior to and after colonisation with Dyella. Conclusion: Bacteria of genus Dyella can colonise the CF lung and pose a diagnostic challenge for the clinical microbiology laboratory. The clinical significance of the colonisation is unknown.