Prevalence and detection of mixed-population enterococcal bacteremia.
Mixed-population (heterogeneous) enterococcal bacteremia (MEB) is rarely reported. Based on one occasion in which Vitek2 missed a vancomycin-resistant subpopulation isolated from a patient, we developed a simple method to detect this subpopulation and determined MEB frequency. The four patients presented here had either Enterococcus faecium or Enterococcus faecalis bacteremia caused by both vancomycin-resistant enterococci (VRE) and vancomycin-susceptible enterococci (VSE). No prior common antibiotic therapy was observed, and bacteremia resolved with daptomycin, gentamicin, and/or linezolid treatment. In two cases, VRE presence was missed by Vitek2. To detect the VRE subpopulation, tryptic soy broth was inoculated from positive blood cultures and a saline suspension was inoculated to a vancomycin (6-μg/ml) (V6) plate. Two isolates from each patient were studied further. Relatedness was assessed by multilocus sequence typing, fitness was evaluated by growth curve and competition assays, and vanA presence was determined by PCR. MEB represented ∼5% of all enterococcal bacteremias. All VRE subpopulations grew on V6 plates but were missed in two instances by Vitek2. VRE and VSE isolates from each patient were closely related and did not differ in overall fitness. All four VRE isolates and 2/4 VSE isolates were vanA positive. MEBs occur regardless of prior antimicrobial therapy, are relatively common in our hospital, and are important to detect. As far as we know, this study is the first to report heterogeneous E. faecalis bacteremia. There is a simple method to detect VRE subpopulations that may be missed by Vitek2.
Department of Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA anamaria.cardenas@uphs.upenn.edu.
Ana María
AM
Cárdenas
Department of Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
Kathleen A
KA
Andreacchio
Department of Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
Paul H
PH
Edelstein
D000081:Acetamides / Q000627:therapeutic use; D000368:Aged; D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D016470:Bacteremia / Q000175:diagnosis / Q000453:epidemiology* / Q000382:microbiology; D060085:Coinfection / Q000175:diagnosis / Q000453:epidemiology* / Q000382:microbiology; D017576:Daptomycin / Q000627:therapeutic use; D013293:Enterococcus faecalis / Q000145:classification / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification*; D016984:Enterococcus faecium / Q000145:classification / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification*; D005839:Gentamicins / Q000627:therapeutic use; D016908:Gram-Positive Bacterial Infections / Q000175:diagnosis / Q000453:epidemiology* / Q000382:microbiology; D006801:Humans; D000069349:Linezolid; D008297:Male; D008875:Middle Aged; D058885:Multilocus Sequence Typing; D023303:Oxazolidinones / Q000627:therapeutic use; D015995:Prevalence; D016896:Treatment Outcome; D020713:Vancomycin Resistance
D000081:Acetamides; D000900:Anti-Bacterial Agents; D005839:Gentamicins; D023303:Oxazolidinones; D000069349:Linezolid; D017576:Daptomycin