Poster Abstract: EPS3.01 Is variation in Pseudomonas aeruginosa (Pa) surface-enhanced Raman spectroscopy (SERS) spectra related to phenotype?

Objectives: SERS is a novel technique that produces whole-organism spectroscopic fingerprints at high speed. Variation in the Pa spectra within and between people with cystic fibrosis (PWCF) has been previously noted; however, this variation could not be attributed to differences in straingenotype.1 The objective of this study was to determine if the variation observed in the Pa spectra was related to phenotype.

Methods: Pa isolates (n = 152) were adjusted to an inoculum of 1 ×108−109 CFU/mL, the resulting bacterial pellet was mixed with citrate reduced silver colloid and dried; the Raman spectra was recorded (4 × 10seconds, 785 nm). For each isolate, spectra were compared with morphology, pyoverdine production, biofilm formation and antibiotic susceptibility data. Principal component analysis (PCA) was performed using R. Paisolates (n = 4), cultured from PWCF, were grown under aerobic and anaerobic conditions at pH 5.8, 6.5 and 7 and in sub-minimum inhibitory concentrations (MIC) of azithromycin, aztreonam, ciprofloxacin and tobramycin for 24 and 48 hours and the Raman spectra recorded.

Results: It was not possible to distinguish between the spectra and the different Pa phenotypes using PCA. Differences were observed in the spectra of 4 Pa isolates when grown anaerobically compared to aerobically. However, varying the pH of the media did not change the spectra. Growth in sub-MIC concentrations of antibiotics did not change the SERS spectra of the 4 Pa isolates; apart from one Pa isolate (B049V2S2A) grown in sub-MIC concentration of azithromycin, where the spectra did not have vibrational bands attributable to pyocyanin at either 24 or 48 hours.

Conclusion: SERS is of limited value characterising Pa from PWCF, as it is likely that genomically identical Pa from different oxygen micro-environments in the CF lungs may produce different spectra. pH and antibiotic exposure have no significant impact on Raman spectra.