Strain relatedness in gram-negative bacteremia: Cause or contamination?

Aim: Bloodstream infections are a major cause of mortality, 25% of which are associated with gram-negative bacteremia. To avoid the inappropriate use of antibiotics, it is important to differentiate the bacteremia from contamination. In general, gram-positive bacteria were more likely to be contaminants than gram-negative-bacteria. There is little information in the literature concerning the epidemiology of gram-negative bacteria isolated from sequential blood cultures. Therefore, we aimed to examine the molecular epidemiology of gram-negative bacteria isolated from sequential blood cultures. Material and Methods: A total of 56 patients (112 samples and strains) with two or more sequential positive blood cultures for gram-negative bacteria with the same antibiogram were included in the study. Pulsed-field gel electrophoresis (PFGE) and arbitrarily primed PCR (AP-PCR) were performed for the determination of strain relatedness. Results: While PFGE analysis demonstrated relatedness in 6 isolates, AP-PCR demonstrated 9 relatedness in 112 isolates. Discussion: The results of our study suggest that, although the possibility of contamination is very low in gram-negative bacteremia, this can still take place, as shown in sequential blood cultures with the same antibiogram.