Discussion and conclusions
N. macacae bacteremia is a rare disease, and its entry point and mechanism are often unknown. To our knowledge, there have been 10 specimens of
N. macacae isolated in human samples, including these two cases (Table
3). There have only been two reports of
Neisseria bacteremia in humans including a 5-month-old child and a healthy adult [
1,
2]. This is the first report of two cases of
Neisseria bacteremia in patients with cancer, one of whom had recovered from cancer.
N. macacae is known to reside in the mouth of monkeys [
3]; however, neither of our patients had a history of contact with monkeys. Only one case of infectious endocarditis in an adult with
N. macacae bacteremia was reported [
2].
Table 3
N. macacae isolated in human samples review
1 | F | 42 | Blood culture | Present case 1 |
2 | F | 69 | Blood culture | Present case 2 |
3 | M | 0.66 (8 months) | Blood culture | |
4 | M | 65 | Blood culture | |
5 | F | 52 | Peritoneal fluid culture | |
6 | NA | NA | Mouth | |
7 | NA | NA | Throats swab | |
8 | NA | NA | Respiratory tract | |
9 | NA | NA | Respiratory tract | |
10 | NA | NA | Respiratory tract | |
Previously, reports of
N. macacae infection in humans include peritonitis in patients on peritoneal dialysis [
5]. Addtionally,
N. macacae has been isolated from the upper respiratory tract of neutropenic patients [
4]. No neutropenia or no respiratory infections such as pneumonia and infective endocarditis were observed in our patients. In addition, echoendoscope colonization was reported, suggesting that it may have been established in the upper digestive tract of humans [
6]. Among patients who used antibiotics within a month,
N. macacae accounted for 4.5% of
Neisseria species that colonized in the oral cavity [
4]. Neither of our patients had used antibiotics within 1 month of admission, but both had previously been treated with antibiotics and chemotherapy. In both cases, mucosal damage was observed in the upper gastrointestinal tract. Therefore, exclusion diagnosis suggested that bacteremia invasion was caused by mucosal rupture in our cases.
There are no clear susceptibility testing methods or criteria for N. macacae detection, and the treatment for Neisseria bacteremia is unknown. Therefore, susceptibility testing was performed using the CLSI meningococcal criterion; however, it is unknown whether these results are appropriate. Both patients responded well to treatment with β-lactam antibiotics and improved after 2 weeks. The duration of treatment is unknown. Modifying the treatment based on the source of the infection may shorten the treatment period. Therefore, further research on N. macacae bacteremia is necessary.
Common
Neisseria species that are pathogenic to humans include
N. gonorrhoeae and
N. meningitidis. 16S sequence analysis may not be sufficient to identify
Neisseria species due to high intraspecies sequence variation in the 16S rRNA gene [
4].
Neisseria species can be differentiated based on their morphological, physiological, and biochemical properties and MALDI-TOF MS results. Commensal
Neisseria species that colonize oral and nasal cavity sites have only been rarely associated with disease [
7]. Donati et al. have shown that commensal species have tropism for different sites in the oral cavity and oropharynx.
Neisseria meningitidis is enriched for colonization in the throat,
N. flavescens and
N. subflava populate the tongue dorsum, and
N. sicca,
N. mucosa, and
N. elongata the gingival plaque [
8].
Interestingly, Bennett et al. have demonstrated that
N. subflava and
N. flavescens are phylogenetically the same species. Similarly, researchers have proposed that both
N. sicca and
N. macacae be reclassified as
N. mucosa [
9,
10].
The limitation of this report was that
Neisseria spp. is difficult to fully identify with only 16sRNA. In 34% (29/85) cases of identification of the
Neisseria spp., 16S rRNA sequence analysis indicated the possibility of more than one species [
4]. Therefore, the usefulness of MALDI-TOF for the identification of
Neisseria spp. is being examined. In CASE 2, the 16sRNA analysis results showed that
N. macacae,
N. sicca and
N. mucosa were the three possible species. A combination of biochemical tests ruled out
N. mucosa but did not differentiate N. macacae from N.
sica. However,
N. sica was not within rank 10 on the MALDI-TOF, and therefore
N. macacae was identified.
This case report suggests that N. macacae bacteremia may be caused by gastrointestinal mucosal damage. Scrutiny of the upper gastrointestinal tract should be considered in patients with N. macacae bacteremia caused by an unknown source.
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.