Clinical consequences of using PNA-FISH in Staphylococcal bacteraemia.

To optimize patient treatment and rational use of antimicrobials, it is important to provide fast information on findings in blood-cultures (BCs). The purpose of this study was to evaluate the impact of using peptide nucleic acid fluorescence in situ hybridization (PNA-FISH) on positive BCs containing Gram-positive cocci in clusters to differentiate between Staphylococcus aureus (SA) and coagulase negative staphylococci (CoNS) on the prescribed antimicrobial therapy and on the number of contacts between microbiologist and clinician. All cases of positive BCs in our laboratory with SA or CoNS in the year 2011 were identified and the charts were reviewed retrospectively. The group of patients with BCs tested with PNA-FISH was compared to the group of patients with untested BCs. A total of 200 patients with SA and 725 patients with CoNS were included. The mean number of contacts was 0.82 when PNA-FISH showed CoNS and 1.39 when PNA-FISH was not done (p < 0.0001). More patients were recommended appropriate antimicrobial therapy for SA bacteraemia in the PNA-FISH group (98.0%) than in the non-PNA-FISH group (89.4 %) (p = 0.025). The percentage treated with dicloxacillin was 29.6 in the PNA-FISH group, and 8.2 in the non-PNA-FISH group (p = 0.0003). The use of PNA-FISH on BCs in this study was associated with more appropriate and narrow spectrum antimicrobial therapy for patients with SA in an area with low prevalence of methicillin-resistant SA, and a lower number of contacts between clinical microbiologist and clinician about BCs with CoNS as contaminants.