AUTHOR=Abbas Mohamed , Emonet Stéphane , Köhler Thilo , Renzi Gesuele , van Delden Christian , Schrenzel Jacques , Hirschel Bernard 

TITLE=Ecthyma Gangrenosum: Escherichia coli or Pseudomonas aeruginosa?

JOURNAL=Frontiers in Microbiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2017.00953

DOI=10.3389/fmicb.2017.00953

ISSN=1664-302X

ABSTRACT=<p><bold>Background:</bold> Ecthyma gangrenosum (EG) are necrotic lesions that develop in the context of <italic>Pseudomonas aeruginosa</italic> bacteremia. Isolated reports describe EG in the setting of non-Pseudomonal infections. In a patient with EG, initial blood cultures showed <italic>Escherichia coli</italic>, and almost occulted <italic>P. aeruginosa</italic> bacteremia. Based on the clinical picture we suspected preponderant <italic>P. aeruginosa</italic> bacteremia, outgrown by concomitant low-grade <italic>E. coli</italic> bacteremia in the blood culture vials.</p><p><bold>Methods</bold>: We performed quantitative polymerase chain reaction (PCR) assays with specific primers for <italic>P. aeruginosa</italic> and <italic>E. coli</italic> on blood collected at the same time for blood cultures. We also performed quantitative cultures of the strains isolated from the patient’s blood.</p><p><bold>Results</bold>: Quantitative PCR showed that there were 1.5 × 10<sup>E</sup>7 copies/milliliter (ml) of <italic>P. aeruginosa</italic> DNA, whereas the quantity of <italic>E. coli</italic> DNA was below the detection limit of 2 × 10<sup>E</sup>4 copies/ml. We estimated that there was at least 1000 times more <italic>P. aeruginosa</italic> than <italic>E. coli</italic>. Quantitative cultures showed that <italic>E. coli</italic> grew faster than <italic>P. aeruginosa</italic>.</p><p><bold>Conclusion</bold>: Our patient with EG had preponderant <italic>P. aeruginosa</italic> bacteremia, that was almost occulted by concomitant low-grade <italic>E. coli</italic> bacteremia. Quantitative PCR was complementary to blood cultures in the final microbiological diagnosis, and proved beneficial in establishing the etiology of EG. This may question the existence of non-Pseudomonal EG, and also shows that blood culture results do not always reflect an “exact picture” of what happens in the patient’s blood at the time of sampling. This case illustrates the importance of communication between the clinician and the microbiology laboratory to ensure best possible results.</p>