Neisseria macacae infective endocarditis: first case report in China

Volume 113, Issue 4, December 2025, 117055

Diagnostic Microbiology and Infectious Disease

Author links open overlay panel, , AbstractBackground

: Neisseria macacae is a gram‑negative diplococcus rarely implicated in human disease.

Case Presentation

: We report a case of infective endocarditis in a 60-year-old male with intermittent fever. Physical examination revealed a systolic murmur. Laboratory tests showed significant inflammation. Cardiac ultrasound demonstrated a tricuspid valve vegetation. Blood cultures were positive for N. macacae, identified using VITEK 2 COMPACT, MALDI-TOF MS, and 16S rRNA sequencing. The bacterium was susceptible to ceftriaxone and meropenem. Initial treatment with meropenem, followed by the addition of ceftriaxone after pathogen identification and susceptibility testing, led to significant improvement in inflammatory markers. Subsequent tricuspid valve surgery was successful.

Conclusions

: This case highlights the need to consider N. macacae in unexplained fever or infective endocarditis and underscores the value of advanced microbiological identification techniques.

Introduction

Neisseria macacae (N. macacae) was first isolated from the oral cavity of Macaca mulatta by Vedros in 1983. It is classified within the genus Neisseria, a group of gram-negative, oxidase-positive diplococci[1]. For a long time, this bacterium was regarded solely as an animal colonizer, and reports of its involvement in human infections have been exceedingly rare. In 2014, Schouten reported the first human case of N. macacae bacteremia in a 5-month-old infant, whose infection may have resulted from indirect exposure to zoo personnel[2]. In 2017, Maude Vecten reported the world's first case of fatal infective endocarditis (IE) attributable to this bacterium[3]. In 2020, Yamamoto reported two additional cases of N. macacae bacteremia in cancer patients. Significantly, both patients exhibited upper digestive tract mucosal damage, which provides important insights into the potential infection route of this bacterium[4].

To date, confirmed cases of N. macacae IE have not been reported in China. This paper presents a detailed case report of IE with concomitant bacteremia attributed to N. macacae, analyzing its clinical manifestations, microbiological identification, and treatment process. This report aims to enhance clinical recognition of this rare pathogen and provide evidence-based guidance for the diagnosis and treatment of analogous cases.

Section snippetsCase description

The patient was a 60-year-old male with a recent history of gingival swelling and pain. He was admitted to the hospital due to "intermittent fever for 3 weeks". Admission physical examination: body temperature 39.5 °C, pulse 102 beats per minute, respiration 20 breaths per minute, blood pressure 130/85 mmHg. Laboratory tests showed a significant inflammatory response: procalcitonin (PCT) was 9.878 ng/ml (normal <0.5 ng/ml), C-reactive protein (CRP) was >212 mg/L (normal <8 mg/L), ferritin was

Discussion

N. macacae is an extremely rare human pathogen, with only a limited number of cases reported globally to date[2,4]. The pathogenic mechanism of N. macacae remains unclear. This bacterium may enter the bloodstream via mucosal damage in the upper respiratory or gastrointestinal tracts, potentially causing invasive infections[4,6]. Although the current evidence is limited to sporadic case reports, the possibility that N. macacae can asymptomatically colonize humans should not be overlooked. Its

Conclusion

N. macacae infections in humans are uncommon, but the organism’s pathogenic potential should not be underestimated. Clinicians should consider N. macacae in cases of unexplained fever, bacteremia, or infective endocarditis. Precise microbiological identification and prompt initiation of appropriate antimicrobial therapy are essential for optimizing patient outcomes.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability

The original contributions presented in the study are included in the article. Further inquiries can be directed to the corresponding authors.

Ethics approval and consent to participate

Written informed consent was obtained from the patient for the publication of this case report and accompanying images.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Author statement

All authors have made substantial contributions to the conception or design of the work. All authors have approved the final version to be published; and agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

CRediT authorship contribution statement

Yanjun Zhang: Writing – original draft. Dong Yang: Investigation, Data curation. Wei Wang: Writing – review & editing, Supervision, Conceptualization.

Declaration of competing interest

All authors have approved the manuscript and agree with its submission. We have no conflicts of interest to disclose.

Acknowledgements

We would like to thank the participants in this study.

References (8)L. Walsh et al.Beyond the usual suspects: reviewing infections caused by typically-commensal Neisseria species

J Infect

(2023)

N.A. Vedros* et al.Neisseria macacae sp. nov., a new Neisseria species isolated from the oropharynges of rhesus monkeys (Macaca mulatta)

Int J Syst Evol Microbiol

(1983)

M.A. Schouten et al.Neisseria macacae bacteraemia in a child with fever and petechiae

Ned Tijdschr Med Microbiol