Neisseria mucosa is a gram negative diplococcus belonging to the genus Neisseria found commonly in the upper respiratory tract. It is typically a commensal organism when it is parasitic on oral and nasal mucosa. To our knowledge, it does not cause disease in healthy individuals with normal immunity, but can be pathogenic in those with impaired immune function or change in bacterial colonization site. Neisseria mucosa has been reported to cause bacterial meningitis, conjunctivitis, pneumonia, endocarditis, peritonitis and urethritis. However, peritoneal dialysis-related peritonitis caused by Neisseria mucosa is extremely rare in clinical practice, which has not previously been reported in China.

A 55-year-old female presented to the nephrology clinic with upper abdominal pain without apparent cause, accompanied by nausea, vomiting and diarrhea for two days. The patient had a history of Stage 5 chronic kidney disease for five years, combined with renal hypertension and renal anemia, and was treated with peritoneal dialysis for renal replacement therapy. The patient was subsequently diagnosed with peritoneal dialysis-related peritonitis. Routine examination of peritoneal dialysis fluid showed abdominal infection, and the results of microbial culture of the peritoneal dialysis fluid confirmed Neisseria mucosa. Imi-penem/ cilastatin 1.0 g q12h was added to peritoneal dialysis fluid for anti-infection treatment. After 24 d, the patient underwent upper extremity arteriovenous fistulation. One month later, the patient was discharged home in a clinically stable state.

Peritonitis caused by Neisseria mucosa is rare. Patients with home-based self-dialysis cannot guarantee good medical and health conditions, and require education on self-protection.

The Gram-negative diplococci Neisseria are commensal bacteria of mucosal surfaces in humans[1]. Two major subspecies, Neisseria meningitidis and Neisseria gonorrhoeae, are pathogenic in humans, while most other subspecies such as Neisseria mucosa are recognized as non-pathogenic. Neisseria mucosa is generally not pathogenic in healthy individuals with normal immunity, but can be pathogenic in those with impaired immune function or changes in bacterial colonization sites.

It has been reported that Neisseria mucosa is associated with meningitis, endocarditis, pneumonia, bacteremia, arthritis, peritonitis, endophthalmitis and urethritis[2-7]. We herein report the first case of refractory peritoneal dialysis-related peritonitis caused by Neisseria mucosa in mainland China.

Combined with the patient’s medical history, the final diagnosis was peritoneal dialysis-related peritonitis caused by Neisseria mucosa.

For adequate coverage of Gram-positive and Gram-negative organisms, the empirical antibiotic therapy given was vancomycin 1000 mg qd combined with imipenem/cilastatin 1.0 g q12h added to peritoneal dialysis fluid. In addition, 2.5% dialysate 2 L + 1.5% dialysate 6 L/d continuous ambulatory peritoneal dialysis was carried out to eliminate toxins and maintain water, electrolyte, and acid-base balance. Vancomycin was discontinued after the pathogen was identified, and imipenem/cilastatin injection 1.0 g q12h for anti-infection treatment was continued. After 8 d, the patient's dialysate was clear and her condition had improved. Ceftazidime injection 1.0 g qd was added to the dialysate for follow-up anti-inflammatory treatment.

On the 24^th day of hospitalization, arteriovenous fistulation of the upper extremity was performed. The purpose of surgical treatment is to change his treatment plan from peritoneal dialysis to hemodialysis three months after the operation. The patient was discharged in a stable condition after one month. Two weeks after discharge, the patient was again hospitalized due to peritoneal dialysis-related peritonitis. The same organism-Neisseria mucosa was cultured from the patient's peritoneal dialysis fluid. After a detailed medical history enquiry, it was found that the patient frequently used her mouth to open the cap of the dialysate bottle during peritoneal dialysis at home. During her second hospitalization, the patient was treated with imipenem/cilastatin injection 1.0 g q12h added to peritoneal dialysis fluid for 20 d and was cured. The patient is currently undergoing close follow-up observation.

Neisseria species other than Neisseria meningitidis and Neisseria gonorrhoeae, such as Neisseria mucosa, Neisseria subflava, Neisseria lactamica, Neisseria cinerea, and Neisseria mucosa, are unusual pathogens in humans[8]. Neisseria mucosa, originally described as Diplococcus mucosus by von Lingelsheim in 1906, frequently colonizes the nasopharynx and dolphin respiratory tract[9]. It was gram-negative diplococcus, with large colonies and mucus type, often fused together. Most strains do not produce pigment, or light gray to light yellow. It can decompose glucose, maltose, fructose and sucrose. It is difficult to distinguish from Neisseria mucosa during mass spectrometry identification. Based on whole genome sequencing analysis, Neisseria mucosa is the same species as Neisseria rhesus and Neisseria mucosa, and Neisseria mucosa has priority naming rights. Therefore, we further identified the pathogen of this infection as Neisseria mucosa by 16sRNA sequencing, combined with biochemical reaction characteristics and colony morphology. According to the literature, Neisseria can cause meningitis, conjunctivitis, pneumonia, endocarditis, urethritis and peritonitis[2-6]. There are few reports of peritoneal dialysis-related peritonitis caused by Neisseria mucosa. To our knowledge, the first case was reported in 1993 and only 5 cases have been reported so far. Patients were aged 17 to 68 years, with no specificity, and ultimately received effective treatment[10-14]. This is the first case report of peritoneal dialysis-associated peritonitis caused by Neisseria mucosa in mainland China.

The patient was diagnosed with Stage 5 chronic kidney disease, combined with renal hypertension, renal anemia, and maintenance peritoneal dialysis for more than 5 years. Therefore, the patient's immune function and nutritional status were poor, and the peritoneal self-defense function was impaired. Combined with the significant increase in systemic infection indicators, the leukocytes in peritoneal dialysis fluid were chemotactic and were mainly polymorphonuclear neutrophils. Bacterial smears and culture results confirmed the diagnosis of peritoneal dialysis-associated peritonitis caused by Neisseria mucosa.

The patient was treated with antibiotics added to peritoneal dialysis fluid for anti-inflammatory treatment. According to the Clinical and Laboratory Standards Institute[3], there is no accepted standard for assessing the antimicrobial sensitivity of Neisseria mucosa. We provide in vitro drug sensitivity test results for reference: Penicillin G (0.125 μg/mL), ceftriaxone (0.25 μg/mL), meropenem (0.125 μg/mL), combined with the International Society of Peritoneal Dialysis (ISPD) guidelines for the treatment of abdominal infection[15], the first treatment with imipenem/cilastatin resulted in significant improvement, and 8 d after treatment with ceftazidime, the clinical symptoms disappeared.

However, the patient was readmitted to hospital due to peritonitis caused by Neisseria mucosa two weeks later, according to ISPD peritonitis guideline recommendations in 2022[16]. The patient's second infection was defined as a relapse. The reason for the second infection may be that the first treatment did not involve removal of the peritoneal dialysis tube, resulting in a small amount of bacterial colonization. In addition, after a detailed medical history enquiry, it was found that the patient frequently used her mouth to open the cap of the dialysate bottle during peritoneal dialysis at home. Therefore, it is speculated that the patient's Neisseria mucosa was derived from the peritoneal dialysis fluid contaminated by her own saliva and caused repeat peritonitis.

In summary, we report a case of peritoneal dialysis-related peritonitis caused by repeated infection with Neisseria mucosa. There are few reports on infections caused by Neisseria mucosa. The pathogenic mechanism, infection route and treatment plan of Neisseria mucosa require further study. Peritoneal dialysis patients, due to long-term impaired renal function and low immunity, should pay attention to the prevention of peritonitis. In particular, in home-based self-dialysis patients, medical and health conditions are poor; thus, education on relevant protective measures is needed.

Peritoneal dialysis patients, due to long-term impaired renal function and low immunity, should pay attention to the prevention of peritonitis. Neisseria mucosa, as part of the normal flora of the human oral cavity, rarely causes infection in the body, especially the abdominal cavity. Peritonitis caused by Neisseria mucosa is very rare. Neisseria mucosa was detected during two hospitalizations for peritonitis in this case, which may have been related to the patient's habit of opening the peritoneal dialysis fluid cap using her mouth. Unfortunately, we were unable to confirm whether Neisseria mucosa from the patient's mouth was the same strain as the two isolated strains. However, this case demonstrates that home-based self-dialysis patients, because they cannot guarantee good medical and health conditions, need to be repeatedly educated and protected.