P274 Identification of blaOXA-23 in a mucoid XDR Acinetobacter baumannii isolated from a patient with cystic fibrosis

Acinetobacter baumannii, an ever-increasing threat to public health, possesses the blaOXA-23 carbapenemase, endemic in Italy. Although rarely observed in cystic fibrosis (CF) patients, A. baumannii producing OXA-23 has been sporadically detected in CF patients. Here we describe the methods used to detect blaOXA-23 in a mucoid A. baumannii infecting the lung of a 23-year-old CF patient who came to our center after undergoing segmentectomy for right spontaneous hypertensive pneumothorax. Patient sputum culture shows a mucoid A. baumannii identified by MALDI-TOF mass spectrometry. The antibiogram is performed with Vitek2 and Sensititre® DKMGN broth microdilution. The following tests are also performed: NG-Test® CARBA-5 immunochromatographic test, modified Hodge’s test, real time PCR Xpert® Carba, and homemade PCR for blaOXA-23 gene detection. A. baumannii antibiogram shows an Extensively Drug Resistant (XDR) antibiotype, susceptible exclusively to colistin. Immunochromatographic assay and real time PCR Xpert® Carba are negative. Homemade PCR with blaOXA-23 specific primers yields an amplificate that, after electrophoretic run on agarose gel, shows a 500 bp band concordant with blaOXA-23 amplicon size. Critical observation of common assays may be necessary, as correct detection of the blaOXA-23 gene requires specific analysis. A prompt and correct diagnosis of resistance mechanisms expressed by MDR/XDR microorganisms is necessary not only to prevent the microorganism spread in hospital setting, but also to support the clinician in choosing the most appropriate therapy according to antimicrobial stewardship. Ultimately, in this patient case, the detection of the carbapenemase OXA-23 by means of a homemade molecular test with specific primers guided the clinicians in setting up an anti-Pseudomonas therapy that did not use colistin, the only resource against the A. baumannii strain.