Introduction
Neisseria macacae is a gram-negative diplococcus colonized in the oral cavity of monkeys. Finding N. macacae in patients’ specimens may cause suspicion of patients’ exposure to monkeys. We encountered a case of N. macacae isolated in a patient’s peritoneal dialysate effluent that demonstrated how the Neisseria taxonomy can be misleading.
Methods
The 31-year-old male is a previous anabolic steroid user who was diagnosed as having end-stage renal disease secondary to biopsy-proven focal segmental glomerulosclerosis. Fifty days after his peritoneal dialysis catheter insertion, he complained of one-day history of cloudy dialysate effluent, which was sent for laboratory analysis. The effluent’s total nucleated count (TNC) was 13504 x 10^6/L, with 0.97 neutrophil and 0.03 monocyte/macrophage. The effluent was inoculated in an aerobic blood culture bottle which showed growth after 30 hours of incubation. Gram staining of the culture fluid showed moderate polymorphonuclear leukocytes in addition to gram-negative diplococci under 1000x magnification. He received one intraperitoneal dose of ceftazidime 1.5 g and vancomycin 2 g.
Results
After 24-hour incubation, this microorganism was identified as Neisseria macacae by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (score>2.0). Subsequently, 16S ribosomal RNA testing identified this microorganism as Neisseria macacae/perflava. N. macacae/perflava are usually non-pathogenic commensal flora in the oropharynx of rhesus macaques. However, the patient denied exposure to monkeys. A review of the Bruker manufacturer MALDI-TOF library showed limitations in differentiating between Neisseria macacae and Neisseria sicca, a commensal flora. In three days, his dialysate effluent TNC decreased to 93 x 10^6/L. He subsequently received 18 intraperitoneal doses of ceftriaxone 1 g daily and clinically improved.
Conclusions
This case demonstrated the importance of clinical correlation in interpreting test results and diagnosing zoonotic diseases.
