(490) Evaluation of the Biofire Filmarray Pneumonia panel plus for diagnosis of lower respiratory tract infections of cystic fibrosis transplanted patients

Background: Syndrome-specific, diagnostic panels have potential to provide quick etiological information about lower respiratory tract infections. Lower respiratory samples collected from cystic fibrosis (CF) transplanted patients were evaluated with the newly developed Biofire® Filmarray® Pneumonia Panel plus (Biomérieux) testing for 27 bacteria and viruses that cause pneumonia and other lower respiratory tract infections, as well as for 7 genetic markers of antibiotic resistance. This molecular approach could improve quick diagnosis of lung infections, including virus and some unculturable microorganisms, in critically CF patients such as lung transplanted subjects.

Methods: Forty-one tract samples collected from 26 CF lung transplanted patients in clinical stable conditions (median age 39 years, range 18-60) were analyzed by both standard microbiological methods, and by the multiplex PCR assay.

Results: Results obtained with the panel displayed 75.6% of agreement with standard methods. In 10 (24.4%) cases there was a discrepancy between the two approaches. In four samples bacterial pathogens (2 Staphylococcus aureus, 1 Streptococcus pneumoniae and 1 Serratia marcescens) were not isolated with the conventional cultural techniques. Occurrence of bacterial variant with a poor growth, selected by the CF environment, could explain this data. Isolation problems due to concomitant growth of other bacteria should also taken into account. In six samples the multiplex PCR assay missed relevant bacteria: 4 Pseudomonas aeruginosa, 1 Enterobacter cloacae and 1 S. marcescens. This discrepancy could be explained by bacterial load, in fact the number of CFU/ml, evaluated with a semi-quantitative analysis included in the conventional approach, was about 10³ for P. aeruginosa, E. cloacae and S. marcescens in these 5 samples, on the other hand the panel is not set to reveal numbers of bacterial DNA below 10⁴ copies /mL.

Conclusions: This molecular approach could have potential to offer support in clinical decision-making with a markedly faster turn-around-time than standard methods, which is perhaps the most important advantage, as well as increased detection of viruses, atypical bacterial pathogens and markers of antibiotic resistance. However, this method has relevant limitations, in fact it is not set do detect few bacterial cells. Detection of low bacterial load is clinically relevant for transplanted CF patients and in the early phases of P. aeruginosa lung infection. This aspect is extremely significant also for other clinical settings.

Acknowledgements: This work was supported by the Tuscany Region [grant number K37, K35].

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