Rapid syndromic approach to diagnosis of bacteremia – results of the first experience

Objective.

To describe results of the first experience of using a syndromic approach to the diagnosis of bacteremia using multiplex panels for real-time polymerase chain reaction (real-time PCR).

Materials and Methods.

The prospective study included 10 consecutive positive blood cultures obtained from 10 patients in the intensive care unit after cardiac surgery. Hemocultures were carried out in BacT/ ALERT FA Plus vials using a BacT/ALERT 3D 120 incubator (bioMérieux, France). After short subcultivation on blood agar (4-6 hours), monocultures were identified using a MALDI-ToF mass spectrometer Vitek MS (bioMérieux, France) with sensitivity to antimicrobial drugs determined on a Vitek-2 compact analyzer (bioMérieux, France). The production of carbapenemases was detected phenotypically using a modified carbapenem inactivation method (mCIM test); the molecular type of enzymes was determined using immunochromatographic tests (NG-Test CARBA 5, NG Biotech, France). In parallel with the described process of identifying microorganisms and determining their sensitivity to antibiotics, positive blood cultures were analyzed using a FilmArray 2.0 analyzer and multiplex real-time PCR panels BioFire FilmArray BCID2 (bioMérieux, France).

Results.

Using MALDI-ToF mass spectrometry, the following microorganisms were identified in the studied blood cultures: K. pneumoniae (n = 5), E. faecalis (n = 2), A. baumannii (n = 1), Raoultella ornithinolytica (n = 1) and S. aureus (n = 1). ⁴⁄₅ (80%) of K. pneumoniae isolates were resistant to carbapenems; another 1 isolate produced an ESBL and remained sensitive to carbapenems. All carbapenem-resistant K. pneumoniae gave a positive result of the mCIM test, while the immunochromatographic method detected the production of carbapenemases of the molecular types NDM (n = 1), KPC (n = 1), as well as combinations of KPC + OXA-48 (n = 1) and NDM + OXA-48 (n = 1). All E. faecalis were sensitive to ampicillin, isolates of A. baumannii and R. ornithinolytica remained sensitive to carbapenems, S. aureus was sensitive to cefoxitin. Using the real-time PCR, ⁹⁄₁₀ (90%) pathogens were identified to species level in 10 positive blood cultures. In the remaining 1 case (R. ornithinolytica, not included in the list of detected species), the microorganism was assigned to the order Enterobacterales. The data obtained by the traditional method completely coincided with the results of real-time PCR analysis, while the time to obtain results was statistically significantly shorter compared to traditional microbiological method (22 hours versus 49 hours, p < 0.001). In ⁷⁄₁₀ (70%) cases, based on the results of real-time PCR analysis, a decision was made to change the tactics of antibiotic therapy.

Conclusions.

Real-time PCR analysis using BCID2 panels is an effective and reliable tool for the etiological diagnosis of bacteremia.