Can Enterobacter (a type of bacteria) cause the presence of nitrate in urine?

Enterobacter and Nitrate in Urine

Yes, Enterobacter can cause the presence of nitrate in urine as it is a gram-negative enteric bacterium capable of reducing nitrate to nitrite, which is detected in urinalysis as a positive nitrite test. 1, 2

Mechanism of Nitrite Production in UTI

• Enterobacter, like other gram-negative enteric bacteria, possesses nitrate reductase enzymes that metabolize urinary nitrates (from dietary sources) into nitrites 1, 3
• This nitrite conversion requires sufficient exposure time of bacteria to urine, which is why the test may be less sensitive in infants who void frequently 1, 2
• The presence of nitrites in urine is specifically associated with gram-negative enteric bacteria, including Enterobacter species 2, 4

Diagnostic Significance

• The nitrite test has high specificity (98%) but limited sensitivity (53%) for detecting urinary tract infections 2, 5
• A positive nitrite test strongly suggests UTI caused by nitrate-reducing bacteria like Enterobacter 2, 5
• However, a negative nitrite test does not rule out UTI, as some uropathogens (like Enterococcus) do not produce nitrites 5, 6
• For optimal diagnostic accuracy, nitrite testing should be combined with other parameters:
  • Leukocyte esterase testing (increases combined sensitivity to 93%) 2, 7
  • Microscopy for pyuria and bacteriuria 2, 5
  • Urine culture (gold standard) 1, 4

Clinical Considerations

• Enterobacter and other gram-negative enteric bacteria are the most common cause of nitrite-positive urinary tract infections 4, 8
• False-negative nitrite results may occur despite infection with nitrate-reducing bacteria like Enterobacter due to:
  • Insufficient bladder incubation time (especially in infants) 1, 2
  • Dilute urine 4
  • Lack of dietary nitrate 4, 3
  • Presence of ascorbic acid or other interfering substances 4
• In pediatric patients with risk factors for UTI, a positive nitrite test strongly suggests infection with gram-negative bacteria rather than Enterococcus 6, 8

Practical Applications

• The nitrite test can help guide initial clinical suspicion but should not be used alone to rule in or rule out UTI 1, 2
• According to the American Academy of Pediatrics guidelines, diagnosis of UTI requires both urinalysis suggesting infection (pyuria and/or bacteriuria) and positive urine culture with ≥50,000 CFU/mL of a uropathogen 2
• Empiric antibiotic selection should not be based solely on nitrite results 9, 8
• For definitive diagnosis, urine culture remains the gold standard 2, 4