Which bacteria do not produce nitrites?

Bacteria That Do Not Show Nitrites in Urinalysis

Gram-positive bacteria, particularly Enterococcus species, do not produce nitrites in urine and will consistently show negative nitrite results on urinalysis testing. 1

Bacteria That Do Not Produce Nitrites

• Enterococcus species (including E. faecalis and E. faecium) are the most clinically significant bacteria that do not reduce nitrate to nitrite in urine 1, 2
• Streptococcus species generally do not reduce nitrate to nitrite, with the exception of S. sanguis which can reduce nitrite (but not nitrate) when grown with hematin 3
• Some strains of Neisseria species reduce nitrite but not nitrate, making them unable to produce a positive nitrite test 3
• Staphylococcus saprophyticus often produces negative nitrite tests despite being a common cause of UTIs 4

Clinical Significance in UTI Diagnosis

• The nitrite test has high specificity (98%) but low sensitivity (53%) for detecting UTIs, primarily because not all uropathogens produce nitrites 4
• Among children with nitrite-negative UTIs, approximately 3.2% are caused by Enterococcus species 1
• The nitrite test is particularly insensitive in:
  • Infants who empty their bladders frequently (insufficient time for nitrate conversion) 4
  • Infections with non-nitrite-producing organisms 4

Mechanism of Nitrite Production

• Nitrite-positive bacteria convert dietary nitrates to nitrites through bacterial reductase enzymes 4
• This conversion requires approximately 4 hours of bacterial exposure to urine in the bladder 4
• Gram-negative enteric bacteria (like E. coli) efficiently convert nitrate to nitrite 1, 5
• Some bacteria (like Veillonellae and Haemophilus) reduce nitrate much more rapidly than they reduce nitrite, leading to nitrite accumulation 3

Diagnostic Implications

• A negative nitrite test has little value in ruling out UTI due to its low sensitivity 4
• Combined testing with leukocyte esterase improves sensitivity - when either test is positive, sensitivity increases to 93% 4
• Despite Enterococcus not producing nitrites, the prevalence of enterococcal UTIs is low enough (2.1% of all UTIs) that empiric antibiotic choice should not be altered based solely on a negative nitrite test 1
• Among children with positive leukocyte esterase but negative nitrite, only 0.7% of cases had enterococcal UTI 1

Recommendations for Clinical Practice

• Always use nitrite testing in conjunction with other urinalysis parameters (leukocyte esterase, microscopy) and urine culture 4
• Consider that a positive nitrite test is highly specific for UTI (few false positives) 4
• Remember that a negative nitrite test does not rule out UTI, especially in infants or when suspecting infection with Enterococcus, Streptococcus, or Staphylococcus saprophyticus 4, 1
• For highest diagnostic accuracy, combine leukocyte esterase test, nitrite test, and microscopy (99.8% sensitivity) 4