Is Neisseria lactamica (N. lactamica) pathogenic in urine?

Is Neisseria lactamica Pathogenic in Urine?

Neisseria lactamica is not considered a urinary pathogen and should generally be regarded as a contaminant or colonizer when isolated from urine, except in rare cases involving severely immunocompromised patients.

Understanding N. lactamica Biology

• N. lactamica is a nonpathogenic commensal organism that normally colonizes the human upper respiratory tract, particularly the nasopharynx 1
• This organism is specifically mentioned in CDC guidelines as a commensal species that can cause false-positive results when using nucleic acid amplification tests (NAATs) for Neisseria gonorrhoeae detection, highlighting its benign nature 2
• The organism has been associated with protection against N. meningitidis colonization and disease, further supporting its non-pathogenic role 1

Clinical Significance in Urine

• N. lactamica has extremely limited pathogenic potential in the urinary tract. The only documented urogenital isolation was a single case report from 1980 describing isolation from vaginal discharge—not urine—in a patient with persistent symptoms 3
• That 1980 case report specifically emphasized the importance of complete biochemical identification to avoid misdiagnosis of gonorrhea, underscoring that N. lactamica itself was not considered the pathogen 3
• Even closely related Neisseria mucosa (another commensal species) has only been reported as a causative agent in "a couple" of UTI cases in highly susceptible individuals with significant underlying conditions 4

When N. lactamica Causes Disease (Not in Urine)

• The only documented pathogenic role for N. lactamica has been in severely immunocompromised hosts, specifically organ transplant recipients 5
• A single case report from India described N. lactamica causing a cavitatory lung lesion and skin rash in a kidney transplant recipient—notably, this was respiratory/systemic disease, not urinary tract infection 5

Clinical Approach to N. lactamica in Urine

If N. lactamica is isolated from urine, consider it a contaminant or colonizer unless:

• The patient is severely immunocompromised (organ transplant recipient, advanced HIV/AIDS) 5
• There is persistent pyuria (≥10 WBCs/high-power field) with clinical symptoms of UTI and no other pathogen identified 2
• The organism is isolated in pure culture with high colony counts (≥10⁵ CFU/mL) on repeated specimens 2

Critical pitfall: The primary clinical significance of identifying N. lactamica is to avoid misdiagnosis as N. gonorrhoeae, which has serious social and medicolegal consequences 2, 3. Ensure your laboratory uses definitive identification methods with at least two different approaches (biochemical, enzyme substrate, or serologic) when Neisseria species are isolated 2.

Recommended Management

• Do not treat N. lactamica isolated from urine in immunocompetent patients 2
• If the patient has true UTI symptoms with pyuria, investigate for other uropathogens including typical Enterobacterales (E. coli, Klebsiella, Proteus), Enterococcus, and Pseudomonas species 2
• In the extraordinarily rare scenario of a severely immunocompromised patient with persistent symptoms and only N. lactamica isolated, the organism would likely be susceptible to broad-spectrum penicillins, cephalosporins, fluoroquinolones, and aminoglycosides based on its commensal nature 4