Pediatric Enterococcal Infection Workup

Updated: Apr 12, 2017
  • Author: Meera Varman, MD; Chief Editor: Russell W Steele, MD  more...
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Workup

Laboratory Studies

See the list below:

  • Diagnosis

    • Enterococcal infections are diagnosed once the organism has been isolated from a blood culture or other normally sterile site. Isolation from a stool culture is not evidence of invasive infection. The significance of isolating Enterococcus from polymicrobial intra-abdominal, wound, and pelvic infections has yet to be determined and studies have not supported the need for empiric enterococcal antimicrobial coverage for these organisms in managing bowel perforations. Test all isolated organisms for resistance to beta-lactam antibiotics, aminoglycosides, and glycopeptides. Multiple antibiotic-resistant isolates also may need to be tested for resistance to fluoroquinolones, quinupristin/dalfopristin, doxycycline, and chloramphenicol.

    • Test ampicillin resistance by determining the minimal inhibitory concentration (MIC) and detecting beta-lactamase production. Although isolates with an MIC of greater than 16 mcg/mL are considered resistant, high doses of ampicillin (≤ 20 g/d in adults) may be effective for MICs as much as 64 mcg/mL. Enterococcus with gentamicin MICs of greater than 500 mcg/mL and streptomycin MICs of greater than 1000-2000 mcg/mL (depending on method used) are considered highly resistant and nonsynergistic for use of the aminoglycoside as part of combination therapy. Vancomycin MICs are difficult to determine, but agar dilution screening using brain-heart infusion agar supplemented with 16 mcg/mL vancomycin is reliable, as is the standard broth microdilution method.

  • Antimicrobial resistance and susceptibility

    • Enterococcus demonstrates 2 types of resistance.

      • Intrinsic resistance (low-level resistance) is chromosomally mediated and nontransferable.

      • Acquired resistance (high-level resistance) is mediated by plasmids and transposons and can be transferred from one bacterium to another.

    • Beta-lactam resistance is due to production of low-affinity penicillin-binding proteins. Enterococci are inherently resistant to cephalosporins, clindamycin, and semisynthetic penicillins, such as nafcillin, oxacillin, and methicillin. All enterococci have intrinsic low-level resistance to aminoglycosides.

    • Vancomycin-resistant enterococci: Three major phenotypes of vancomycin resistance have been described in enterococci.

      • Van A is characterized by high-level resistance to vancomycin (MIC >64 mcg/mL) and teicoplanins (MIC >32 mcg/mL). This phenotype is mediated by a transposon (Tn 1546) that carries 7 genes and is usually seen in E faecium.

      • Van B phenotype has variable levels of resistance to vancomycin (MIC 4-1000 mcg/mL) but not teicoplanin. It is mediated by transposons (Tn 1547). This phenotype usually is seen in E faecium but is also seen in E faecalis.

      • Van C phenotype is limited to certain species of enterococci. This phenotype demonstrates low-level vancomycin resistance (MIC 8-32 mcg/mL) and is susceptible to teicoplanin.

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Imaging Studies

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  • According to the site and type of infection, the following imaging studies may be considered:

    • Brain CT scanning

    • Abdominal CT scanning

    • Renal ultrasonography

    • Heart echocardiography

    • Plain film radiography (eg, chest radiography)

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Procedures

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  • Lumbar puncture or shunt aspiration is recommended to evaluate for meningitis or ventriculoperitoneal (VP) shunt infection.

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