PCR and Sequencing Diagnosis of Infective Endocarditis

The diagnosis and management of infective endocarditis (IE) rely on the assessment of microbiologists and clinicians. Blood culture results are the standard for the selection of appropriate antibiotic treatment. However, up to 31% stay negative because of pre-operative antibiotic therapy and non-growing fastidious pathogens [1]. Therefore, rDNA PCR and sequencing analysis directly on excised heart valves are practised in routine diagnosis [2].

In his recent application note [3], Lustig compiled results from independent studies that used Molzym’s 16S and 18S rDNA PCR and sequencing kits. It is important to note that the method extracts DNA only from intact microorganisms and thus indicates a current infectious state by living pathogens. Three independent studies served for the comparative analysis of results from culture and PCR/sequencing. The overall patient-related positivity of combined blood and valve analysis by culture (189 patients) was 73%. Common IE pathogens accounted for 66.1%, including streptococci, staphylococci and enterococci. The positivity by PCR/sequencing was notably higher than culture (83.2%). Common pathogens made up the largest group (70%). Moreover, rare pathogens including Aggregatibacter actinomycetemcomitans, Coxiella burnetii, Haemophilus parainfluenzae and others were found by culturing (5.8%) and by PCR/sequencing, but at a higher rate (10%). Thus, the molecular method exactly reflected the culturally determined diversity of IE pathogens, albeit at higher sensitivity. These findings are important for the consideration of PCR/sequencing as a standard diagnostic method of IE aetiologies.

Another observation was that the molecular method uncovered a higher rate and diversity of mixed infections than culture. Culture grew Streptococcus bovis together with S. warneri in one case and in another Pseudomonas aeruginosa with S. sanguinis (rate: 1.1%). In contrast, PCR/sequencing addressed mixed infections to seven patients (rate: 3.2%) with combinations of two Gram-positives, Gram-positives with Gram-negatives and Gram-positives with Candida strains.

Molzym’s kits used for the studies have proven reliable in the diagnosis of the diversity of IE-related infections by common, rare and mixed pathogens, irrespective of whether or not they grow in culture. The early provision of results opens the possibility of a timely adjustment to an adequate antibiotic treatment of patients.