Nitrate-Reducing Uropathogens Not Detected by Nitrite Urine Dipstick
Nitrite dipstick positivity occurs when nitrate-reducing uropathogens convert urinary nitrate to nitrite. [1] Several clinically important urinary pathogens do not reduce nitrate to nitrite and therefore can produce nitrite-negative dipstick results. [1]-[4]
Bacteria Commonly Nitrite-Negative on Urine Dipstick
- Enterococcus species (including Enterococcus faecalis). [1], [2], [3]
- Staphylococcus saprophyticus. [2]
- Acinetobacter species. [2], [4]
- Pseudomonas species. [4], [5]
Related Microbes Associated With Nitrite-Negative Results
- Streptococci including Enterococci (do not reduce nitrate to nitrite). [1]
- Candida (does not reduce nitrates to nitrites). [1]
- Neisseria gonorrhoeae. [3]
- Mycobacterium tuberculosis. [3]
Clinical Implication of Nitrite-Negative Results
Nitrite-negative dipstick results do not rule out urinary tract infection because many uropathogens do not produce nitrite. [1], [6]
Mechanistic Basis
Nitrite dipstick testing detects nitrate reduction, which depends on organism-specific nitrate reductase activity. [1], [3]
Common Pitfalls in Interpretation
Nitrite-negative results may occur with nitrate-reductase–negative organisms such as Enterococcus and Pseudomonas even when bacteriuria is present. [1]-[4]
Practical Considerations for Diagnostic Confirmation
Urine culture is needed to identify the causative organism when nitrite is negative but infection remains clinically suspected. [1], [6]