Neisseria lactamica as a novel cause of prosthetic valve endocarditis in an intravenous drug user: A case report

Abstract

Infective endocarditis is a serious complication in people who inject drugs, most caused by Staphylococcus aureus. Gram negative etiologies are rare, and Neisseria lactamica, a commensal of the nasopharynx, has not previously been reported as a cause of infective endocarditis. A 34-year-old man with a history of intravenous drug use, hepatitis C, and recurrent tricuspid valve infective endocarditis presented with petechial rash, fatigue, and dyspnea. Blood cultures grew N. lactamica, and echocardiography revealed new vegetations on a prosthetic tricuspid valve. He was treated with 6 weeks of intravenous ceftriaxone, with resolution of vegetations on follow-up imaging. This is the first reported case of N. lactamica infective endocarditis. Clinicians should consider atypical organisms in people who inject drugs, particularly in prosthetic valve infections. Reporting such cases broadens understanding of rare pathogens and may guide future management.

Introduction

Infective endocarditis (IE) remains a significant cause of morbidity and mortality among intravenous drug users (IVDUs), predominantly involving pathogens such as Staphylococcus aureus, Streptococcus spp., and Enterococcus spp. ¹ Gram-negative organisms, while less frequently implicated, can be associated with severe disease and diagnostic challenges. Among these, Neisseria lactamica, a typically nonpathogenic commensal bacterium of the nasopharynx, is a rare and unexpected etiology of IE. No cases of IE from N. lactamica have been cited in the literature, and its pathogenic potential is not well understood.

People who inject drugs (PWID) are at elevated risk for IE due to repetitive venous access, contaminated injection practices, and frequent colonization with unusual flora. Damage to endocardial surfaces and introduction of nonsterile material into the bloodstream can facilitate bacterial adherence and vegetation formation. While N. lactamica is not typically part of the skin or oral flora, poor hygienic conditions and mucosal breaches (e.g., nasal insufflation with contaminated substances) might explain its entry into the bloodstream in PWID. Due to the overlap of IVDU and HIV, special attention should be paid toward potentially pathogenic, commensal organisms that can be introduced to the bloodstream via IVDU.

N. lactamica is a Gram negative diplococcus commonly found in the upper respiratory tract of infants and young children. It is closely related to Neisseria meningitidis and shares several phenotypic traits, including the ability to colonize the nasopharynx and express outer membrane proteins with immunological cross-reactivity. ² Unlike N. meningitidis, N. lactamica is generally considered avirulent, and invasive infections are exceedingly rare. When such infections occur, they are typically reported in PWID or individuals with disrupted mucosal barriers. ³

Via a thorough literature review, no documented cases citing N. lactamica as a cause of endocarditis in IVDUs were identified, making this case uniquely significant. We present the case of a 34-year-old male presenting with IE caused by N. lactamica. Because this bacterium has never been reported to cause endocarditis, its identification in an high-risk PWID is of note.

Case report

A 34-year-old man with a past medical history of opioid use disorder on methadone, IVDU, hepatitis-C, and recurrent tricuspid valve IE presented with bilateral petechial rash of the feet, generalized fatigue, and dyspnea on exertion for 1 week. At time of presentation, his vitals were stable. The physical exam was positive for a petechial rash of the bilateral lower extremities from the upper thigh to the dorsum of the feet, which spared the palms and soles (Figure 1). The rest of his physical exam was unremarkable. His hemoglobin was 9.8 g/dL, hematocrit 28.8%, albumin 3.3 g/dL, ESR 122 mm/h, and CRP 1.8 mg/L. His history included multiple hospitalizations for methicillin-resistant and methicillin-sensitive S. aureus IE, leading to prosthetic tricuspid valve replacement 2 months prior. His most recent episode of IE was two and a half months prior, for which he completed a course of vancomycin and a subsequent clearing of valvular vegetations.

Figure 1.

Photograph of this patient’s petechial rash of the bilateral lower extremities from the upper thigh to the dorsum of the feet which spares the palms and soles.

A skin biopsy revealed nonspecific findings, and the petechial rash was considered a nonspecific, idiopathic leukocytoclastic vasculitis that resolved during the patient’s hospital course with the use of glucocorticoids. A negative gonococcal and chlamydia test ruled out a gonococcal, infectious cause of the petechial rash. Three days into admission, the patient developed a new fever of 102.3°F. Five days after admission, blood cultures grew N. lactamica prompting the administration of vancomycin and cefepime. Glucocorticoids were stopped for concern of immunosuppression, and the possibility of the rash being secondary to IE was considered. No Osler or Janeway lesions were identified. Seven blood cultures were obtained, two were positive for N. lactamica, MALDI-TOF MS was used for identification, and no confirmatory tests were performed. Antimicrobial susceptibility was not performed. Modified Duke criteria were fulfilled by having two main criteria (two positive blood cultures and evidence of endocardial involvement) alongside two minor criteria (fever >38°C and injection drug use). Follow-up cultures were performed 6 weeks later to document clearance. Transthoracic echocardiography (TTE) revealed a new 0.4 × 0.5 cm echodensity of the septal leaflet of the prosthetic tricuspid valve (Figure 2). Additionally, TTE noted an increased mean tricuspid valve pressure gradient of 17 mmHg and a maximum velocity of 2.44 m/s, both markedly increased from his last TTE 2 months prior. These findings are consistent with prosthetic valve stenosis secondary to IE. Two days later, vancomycin and cefepime were discontinued due to organism identification and the patient was switched to ceftriaxone 2 g daily via IV for 6 weeks. Then, a transesophageal echocardiogram (TEE) revealed progression of the vegetation of the septal leaflet of the prosthetic tricuspid valve to 0.8 × 0.8 cm, with trace tricuspid valve regurgitation noted (Figure 3).

Figure 2.

TTE showing a 0.4 × 0.5 cm echodensity of the septal leaflet of the prosthetic tricuspid valve.

Figure 3.

TEE revealing a vegetation progression to 0.8 × 0.8 cm.

The interventional cardiology team decided against aspiration thrombectomy to remove the vegetations due to the absence of large vegetations, persistent bacteremia, or embolic events. Additionally, his persistent IV drug use provided more reason not to intervene surgically. It was determined that the patient would receive a 6-week course of intravenous ceftriaxone and was discharged on the 11th day of their admission. A 4-month follow-up TEE showed decreased posterior leaflet mobility but clearance of the vegetation on the septal leaflet of the prosthetic tricuspid valve. The patient has not had recurrence of IE. Substance use treatment was offered but deferred by the patient (Figure 4).

Figure 4.

Timeline detailing the patient course discussed in the manuscript.

Discussion

A review of the literature confirms that N. lactamica is a rare cause of invasive infection, with few cases reported to date. One report described N. lactamica isolated from blood cultures in a postkidney transplant, immunocompromised patient with cavitary lung lesions. The patient responded well to ceftriaxone therapy, demonstrating the organism’s susceptibility to third-generation cephalosporins. ⁴ Another case detailed N. lactamica-associated bacteremic pneumonia in an individual with liver cirrhosis. ⁵ Additionally, N. lactamica has been implicated in septic arthritis and bacteremia in a patient with multiple myeloma receiving immunosuppressive therapy. ⁶

While N. lactamica has not previously been reported as a causative agent of IE, parallels can be drawn from related Neisseria species such as N. sicca and N. elongata, which have been infrequently associated with IE in IVDU. ⁷ These cases, though uncommon, suggest that even typically nonpathogenic Neisseria species may become opportunistic pathogens under certain conditions, particularly in high-risk populations. Also, given the rarity of this pathogen, only having two of seven cultures showing positive results presents the possibility that the positive blood cultures in this case were contaminants. Nonetheless, N. lactamica are not typical skin flora that are more prone to contaminating blood cultures suck as Coagulase-negative Staphylococcus species.

Currently, there are no standardized treatment guidelines for N. lactamica endocarditis. Management decisions must therefore be individualized, relying on antimicrobial susceptibility data and the patient’s clinical status. In the limited cases described above, N. lactamica has generally exhibited sensitivity to third-generation cephalosporins such as ceftriaxone, along with penicillins and fluoroquinolones. Surgical intervention may be warranted in complicated cases involving valvular destruction, persistent bacteremia, or heart failure. In the absence of such complications, a prolonged course of targeted intravenous antibiotics may be sufficient, as was the case in our patient.

Given the rarity of N. lactamica as a pathogen and the lack of robust clinical guidelines, multidisciplinary collaboration and close microbiological monitoring are essential. Moreover, reporting such cases is critical to expanding our understanding of this organism’s pathogenic potential and informing future diagnostic and therapeutic strategies.

Conclusion

As the opioid epidemic continues to evolve, clinicians may increasingly encounter atypical organisms in cases of IE, particularly due to the introduction of noncommensal or environmental pathogens through nonsterile injection practices. This case underscores the importance of maintaining a broad differential when evaluating culture-positive IE, especially when initial empiric regimens fail or when uncommon organisms are isolated.

Supplemental Material

sj-pdf-1-sco-10.1177_2050313X261430801 – Supplemental material for Neisseria lactamica as a novel cause of prosthetic valve endocarditis in an intravenous drug user: A case report

Supplemental material, sj-pdf-1-sco-10.1177_2050313X261430801 for Neisseria lactamica as a novel cause of prosthetic valve endocarditis in an intravenous drug user: A case report by Joseph Ragan, Fariha Hasan, Satyajeet Roy and Maher Al-Safadi in SAGE Open Medical Case Reports