Emery Haley, PhD, Scientific Writing Specialist
Enterobacter group [Klebsiella aerogenes (previously known as Enterobacter aerogenes), and Enterobacter cloacae]
Clinical Summary
- Enterobacter Group organisms are recognized as classical gram-negative, urease-positive, biofilm-forming, uropathogens.
- Enterobacter Group organisms are associated with complicated and recurrent UTI (the same population for which the Guidance® UTI assay is indicated).
- In symptomatic UTI patients, Enterobacter Group organisms:
- Are not contaminants (are found in catheter-collected urine specimens).
- Are viable (can grow out on culture).
- Are pathogenic (associated with elevated urine biomarkers of infection).
- Extended-spectrum beta-lactamase (ESBL)-producing multi-drug resistant urinary isolates of Enterobacter Group organisms are common.
- Reported severe complications of UTIs caused by Enterobacter Group organisms include pyelonephritis, bacteremia, and urosepsis.
Bacterial Characteristics
Gram-stain
Gram-negative (both)
Morphology
Coccus (both)
Growth Requirements
Non-fastidious (bothgrow well in standard urine culture conditions)
Facultative anaerobe
Nitrate Reduction
Yes (both)
Urease
Positive (both)
Biofilm Formation
Yes (both)
Pathogenicity
Colonizer or Pathobiont
Clinical Relevance in UTI
In the Guidance® UTI assay, the Enterobacter Group specifically encompasses two species, Enterobacter cloacae and Klebsiella aerogenes. These are both urease-positive,[1] biofilm-forming, nitrite-positive, non-fastidious, gram-negative, facultative anaerobes classically recognized as uropathogens.[2]
E. cloacae
- E. cloacae is capable of adherence to and intracellular invasion of epithelial cells of the urinary tract, particularly the bladder and kidney.[3] E. cloacae has also been implicated in the formation of calcium oxalate kidney stones.[4] E. cloacae UTI may result in severe complications, including bacteremia, urosepsis,[5] and, in rare cases, infective endocarditis [6]. Enterobacter species, including E. cloacae, are among the six so-called “ESKAPE pathogens” identified as critical multi-drug resistant bacteria requiring urgent development of effective therapeutics.[7] Recent rises in the frequency of fosfomycin-resistant and extended-spectrum beta-lactamase (ESBL)-producing multi-drug resistant E. cloacae urinary isolates are of particular concern.[2,8]
K. aerogenes
- K. aerogenes (previously called Enterobacter aerogenes) is a common cause of UTIs, particularly recurrent UTIs.[9,10] Many K. aerogenes urinary isolates are extended-spectrum beta-lactamase (ESBL)-producing multi-drug resistant.[2,11] K. aerogenes UTIs may result in severe complications, including pyelonephritis, bacteremia, and urosepsis.[12,13]
The Enterobacter Group
In a study of older adult males and females with clinically suspected complicated UTI, Enterobacter group organisms were detected in both midstream voided and in-and-out-catheter collected specimens indicating that they were truly present in the bladder, not simply a contaminant picked up during voiding.[14] Furthermore, elevated markers of immune system activation in the urinary tract have been measured from the same clinical urine specimens in which Enterobacter group organisms were detected, indicating that the presence of Enterobacter group organisms was associated with an immune response to urinary tract infection.[15–17]
Together, these findings indicate that Enterobacter group organisms should be seriously considered as a uropathogen and demonstrate the value of detecting these organisms, particularly in individuals with recurrent UTI and/or risk factors for complicated UTI.
Treatment
Evidence of Efficacy (Checkmarks): Cefepime, Ciprofloxacin, Doxycycline, Gentamicin, Levofloxacin, Meropenem, Nitrofurantoin, Piperacillin/Tazobactam, Sulfamethoxazole/Trimethoprim, and Trimethoprim.