Streptococcus cristatus: An uncommon cause for a common hospital admission

Common organisms associated with community-acquired pneumonia include Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus. Pneumonia can rarely be caused by an organism such as Streptococcus cristatus, as in our case. This organism belongs to the Mitis group within the Streptococcus genus and typically coexists with humans in the oral cavity. We present a case of Streptococcus cristatus bacteremia and community acquired pneumonia in a previously healthy 40-year-old male, for whom infective endocarditis has been ruled out, and who was successfully treated with ceftriaxone. While most reported cases of Streptococcus cristatus involve infective endocarditis, our case is the first identified instance of community acquired pneumonia caused by Streptococcus cristatus. This case highlights that pneumonia with Streptococcus cristatus, typically considered a commensal in the oral mucosa microbiota of humans, is possible, as seen in our case. Unlike previous cases in the literature, our patient did not have infective endocarditis, which is the common presentation of this bacterium. Instead, he solely presented with pneumonia, marking the first reported case in the literature of Streptococcus cristatus causing pneumonia.


Introduction
Community-acquired pneumonia (CAP) is defined as an infection of the lung tissue in an individual who contracted the infection outside of a healthcare setting.The diagnosis is confirmed through chest X-ray imaging after a patient presents with clinical symptoms of typical pneumonia, such as fever, difficulty breathing, coughing, and sputum production.
Common microorganisms associated with CAP, presenting as typical pneumonia, include Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, group A streptococci, Moraxella catarrhalis, anaerobes, and aerobic gram-negative bacteria.Atypical pneumonia, on the other hand, manifests with a nonproductive dry cough, dyspnea, and extrapulmonary symptoms like headache, myalgia, and sore throat.It is often caused by Legionella pneumophila, Mycoplasma pneumoniae, Chlamydophila pneumoniae, and Chlamydia psittaci [1].
This case report discusses a rare instance of pneumonia caused by Group B Streptococcus, specifically Streptococcus Cristatus (S. cristatus).This organism belongs to the Mitis group within the Streptococcus genus and typically coexists with humans in the oral cavity.The organism's characteristics were first identified in 1991, initially described as "Grampositive, catalase-negative cocci measuring approximately 1 µm in diameter and forming chains" [2].
Instances of infections caused by S. cristatus appear to be uncommon, with only a few reported cases in the literature that can be counted on the fingers.Our case is the first reported instance of pneumonia caused No complication V ceftriaxone (2 g bid) for 13 days then followed by oral levofloxacin (500 mg bid) for total of 6 weeks 3-year-old female with a history of mental retardation and epilepsy [5] Transient bacteremia Blood cultures No complication Amoxicillin-clavulanic acid 2 patients, no information [11] Bacteremia and IE Blood cultures No information No information 15-day-old immunocompetent male [12] Septic arthritis of the wrist  AST: Aspartate Aminotransferase.ALT: Alanine Aminotransferase.TSH: Thyroid Stimulating Hormone.FT3: Free Triiodothyronine.by the S. cristatus microorganism.(Table 1) [2].

Case presentation
A 40-year-old male with no medical history was admitted to the emergency department due to a persistent fever, present for the past five days.The patient reported no complaints of cough, sore throat, hemoptysis, abdominal pain, nausea, vomiting, joint pain, dysuria, urinary frequency, rigors, night sweats, or weight loss.Additionally, there was no recent travel history or exposure to sick contacts.Otherwise, the patient was in good health.
On physical examination, the patient exhibited pyrexia with a fever of 38.2 • C, and few crackles were noted upon auscultation of the right upper lobe.Laboratory investigations revealed microcytic anemia along with an elevated C-reactive protein (CRP) count (Values in Table 2).
A chest radiograph revealed hazy opacities and inhomogeneous infiltrations in the right upper lung zone (Fig. 1).
The patient was admitted to the medical ward's isolation room and screened with blood and sputum cultures for infectious diseases.He was empirically treated with IV Ceftriaxone 2 g once daily and Azithromycin 500 milligram once daily following local antimicrobial guidelines while awaiting laboratory results (Table 2).After two negative Acid-Fast Bacilli (AFB) smears, the patient was removed from isolation.Subsequently, blood culture (1 out 1) results revealed S. cristatus growth after one day, along with the presence of polymorphonuclear leukocytes in the sputum gram stain.(Fig. 2).
The possible diagnosis of pneumonia secondary to S. cristatus bacteremia was established.Empiric antibiotics were discontinued, and the patient was treated with IV Ceftriaxone 2 g daily for seven days.Echocardiography was performed, along with repeated blood cultures after 72 h.
The expected outcome of the treatment plan included symptomatic relief of pyrexia and a reduction in physical examination findings, particularly the crackles in the right upper lobe of the lung.Echocardiography revealed no signs of vegetation on any heart valves.
After 72 h, repeated blood cultures showed no growth.The patient was then discharged on oral amoxicillin-clavulanate 1 g twice daily, following the recommendation of the Infectious Disease department.One month later, the patient returned for an outpatient follow-up with no signs or symptoms of the initial diagnosis.

Discussion
S. cristatus bacteremia is a rare cause of community-acquired pneumonia (CAP) with an unknown etiology.The disease is linked to hematogenous spread through a breach in the oral mucosa lining, possibly attributed to poor oral hygiene.Additionally, the microorganism has been associated with dental caries [3].S. cristatus also plays a crucial role in maintaining the oral microbiota.Studies have demonstrated its antagonizing effect on Streptococcus mutans, a cariogenic microorganism considered a risk factor for cancer and tumor progression [4].
Our case of community-acquired pneumonia (CAP) secondary to S. cristatus bacteremia presented with a low-grade fever persisting for one week without cough.Notable findings included crackles in the unilateral upper lobe of the lung, with significant radiographic evidence of hazy opacities.Given the association of S. cristatus with infective endocarditis, an echocardiography was performed, revealing no signs of endocarditis.The management included empiric antibiotics with IV ceftriaxone and azithromycin.Ceftriaxone was continued for seven days, followed by a course of amoxicillin-clavulanate to maintain remission.There were no additional complications throughout the treatment course, and the overall mortality associated with the infection is low [6].Blood and sputum cultures played a crucial role in establishing the diagnosis in this patient.Treatment with antibiotics and education on the importance of oral hygiene were key factors in successful management, leading to a prosperous discharge with no recurrences of the infection.

Conclusion
This case highlights that pneumonia with S. cristatus, typically considered commensal in the oral mucosa microbiota of humans, is indeed possible, as demonstrated in our case.Unlike previous cases in the literature, our patient did not present with infective endocarditis, which is the common manifestation of this bacterium.Instead, he solely exhibited pneumonia, marking the first reported case in the literature of S. cristatus causing this respiratory infection.
Synovial fluid of the wrist, cultureNo complicationVancomycin for 4 weeks.Aspiration followed by arthrotomy 14-year-old female with 22q11 deletion syndrome and Tetralogy of Fallot[13] PCR 16 s on pulmonary valveBacteremia and IE Pulmonary valve replacement Cefepime + vancomycin + gentamicin replaced after with ceftriaxone + daptomycin

Fig. 1 .
Fig. 1.Chest X-ray demonstrating hazy opacities and inhomogeneous infiltrations in the right upper lung.