Eikenella corrodens isolated from pleural effusion: A case report

Abstract

BACKGROUND

The bacterium Eikenella, classified as a gram-negative member of the phylum Proteobacteria, is distinguished by its rarity, corrosive nature, facultative anaerobic properties, and conditional pathogenicity. It represents the sole species within its genus-Eikenella corrodens (E. corrodens)-and can be found colonizing both human and animal oral and nasopharyngeal regions. Additionally, it occasionally inhabits the gastrointestinal or urogenital tracts. However, its slow growth rate can be attributed to its high nutritional requirements. However, there is an uneven distribution of construction and diagnostic capacity in China which poses undeniable challenges for the clinical examination and analysis of this case, especially in the basic hospitals.

CASE SUMMARY

Here we presented a case of empyema associated with E. corrodens infection in a 67-year-old male patient without any previous history of infectious diseases in our primary hospital in Dongguan district of China. The patient was admitted due to recurrent worsening cough, sputum production, and dyspnea for 3 d, which had persisted for over 20 years. Moreover, the patient experienced a one-hour episode of unconsciousness. Upon admission, immediate comprehensive examinations were conducted on the patient which subsequently led to his admission to the intensive care unit. Meanwhile, the patient presented with drowsiness and profuse sweating along with bilateral conjunctival edema observed during initiation of non-invasive ventilation, suggesting empyema. A significant amount of coffee-colored malodorous pleural fluid was drained during the procedure above and sent to the laboratory department for inspection. Finally, laboratory culture results confirmed the presence of E. corrodens infection in the pleural fluid sample. The patient received antimicrobial therapy until died on day 22 in the hospital.

CONCLUSION

In this report, we presented a case of empyema associated with E. corrodens infection. Multiple courses of morphological examination, viable culture analysis, and biochemical identification revealed its difficulties in detecting distinctive characteristics, as well as a detection model worth promoting. It’s just that there were still certain deficiencies in terms of morphological assessment, biochemical identification, and drug susceptibility testing.

Key Words: Eikenella corrodens; Pleural fluid; Morphology; Viable culture; Biochemical identification; Case report

Core Tip: When encountering pleural effusion infection. In clinical laboratory practice, prioritizing attention towards less common bacteria such as Actinobacillus or Streptobacillus species within the HACEK group is crucial. By extending culture time and enhancing culture conditions to improve the isolation and identification of pathogens, detection rates can be significantly augmented. For laboratories, expediting and accurately identifying pathogens plays a pivotal role in optimizing patient treatment outcomes.

INTRODUCTION

The genus Eikenella, classified under the phylum Bacteroidetes, class β-proteobacteria, order Neisseriales, and family Neisseriaceae, is primarily represented by the sole species Eikenella corrodens (E. corrodens)[1]. This Gram-negative bacterium commonly colonizes the human oral and upper respiratory tract as a commensal organism. Risk factors for E. corrodens infection include immunosuppression, mucosal damage, animal bites, dental procedures, and substance abuse[2]. Infections caused by E. corrodens can affect various anatomical sites such as the upper respiratory tract, pleura, abdominal cavity, joints, bone wounds, and endocardium; occasionally leading to infections in other locations (e.g., gangrenous stomatitis)[3-6].

As well known, the occurrence of E. corrodens invading the pleural cavity without forming a draining sinus is considered rare[7], as shown in Table 1. Consequently, a better understanding of the characteristics of E. corrodens is urgently needed. In this case report, we presented an instance where E. corrodens was isolated from pleural effusion in our hospital. The bacteriological and testing characteristics of E. corrodens were described.

Table 1 Literature review of articles reporting lung infection of Eikinella corrodens.

Ref.	Sole bacteria	Type of study	Location	Forming a draining sinus	Spontaneous	Antibiotics
Hu et al[16], 2020	No	Case report	Lung	Yes	No	Yes
Abellán Martínez et al[17], 2000	Yes	Case report and review	Lung	Yes	No	Yes
Hironaka et al[18], 1998	Yes	Case report	Lung	Unknown	Yes	Yes
Salem et al[19], 1996	Yes	Case report	Lung	Unknown	No	Yes
Fujii et al[20], 1995	Yes	Case report	Lung	Unknown	No	Yes
Hsu et al[21], 1989	Yes	Case report	Lung	Unknown	No	Yes
Moro et al[22], 1988	Yes	Case report	Lung	Unknown	No	Yes
Joshi et al[23], 1991	Yes	Case report	Lung	Unknown	Unknown	Yes

CASE PRESENTATION

Chief complaints

The patient, a 67-year-old male with no previous medical infection history, was admitted due to recurrent exacerbation of cough, increased sputum production, and dyspnea over the past 3 d. Besides, the patient encountered a period of unconsciousness lasting for one hour, meanwhile, the patient presented with somnolence and profuse diaphoresis.

History of present illness

Symptoms, such as recurrent exacerbation of cough, increased sputum production, and dyspnea, started over 3 d. Moreover, the patient encountered a period of unconsciousness lasting for one hour. In addition, the patient presented with somnolence and profuse diaphoresis.

History of past illness

These exacerbated symptoms have lasted for more than two decades.

Personal and family history

The patient denied any family history of illness.

Physical examination

On physical examination, the vital signs were as follows: Body temperature, 35.6 °C; blood pressure, 110/80 mmHg; heart rate, 120 beats per min; respiratory rate, 35 breaths per min. Besides the patient had poor overall nutrition, a thin body, a chronic Sick look, and a dull mind. Furthermore, bilateral conjunctival edema was observed.

Laboratory examinations

Upon admission, peripheral blood gas analysis revealed a PCO₂ level of 67.6 mmHg. Blood tests showed white blood cells 47.42 × 10⁹/L (neutrophils 91%), hemoglobin 110 g/L, platelets 301.00 × 10⁹ /L, CRP > 200.00 mg/L, and PCT 0.32 ng/mL. Renal and liver function indices were within normal range.

Imaging examinations

After admission, a computerized tomography (CT) scan taken revealed developed symptoms suggestive of infection, as shown in Figure 1.

Figure 1 Initial computed tomography scan of the patient (blue arrow).

MULTIDISCIPLINARY EXPERT CONSULTATION

Bilateral conjunctival edema was observed, indicating the presence of carbon dioxide retention and hypercapnia encephalopathy. Comprehensive examinations were promptly conducted and subsequently transferred to the intensive care unit.

Non-invasive ventilation was promptly initiated. Considering the significant right pleural effusion, a bedside ultrasound-guided procedure was performed to alleviate lung compression and mitigate the patient’s respiratory distress. A substantial volume of coffee-colored foul-smelling pleural fluid was drained during the procedure, suggestive of empyema, leading to the initiation of empirical antibiotic therapy for potential co-existing bacterial infection. Routine biochemical analysis confirmed empyema in the pleural fluid sample. The smear and culture of the clinical sample were difficultly established. In the meantime, pathogen culture identification and drug sensitivity testing were conducted.

The specimens were collected via closed drainage after the surgical puncture of the patient, and subsequently, a small portion of which was smeared onto a glass slide for Gram staining. Microscopic examination revealed a significant presence of leukocytes and a few Gram-negative bacteria (Figure 2A).

Figure 2 Eikenella corrodens. A: Eikenella corrodens (E. corrodens) gram stain of from a pleural empyema sample in an observing field under an oil immersion lens (× 100) (blue arrow); B: The observation of E. corrodens colonies in culture cultured for 48 h at 35 °C in a 6%-7% CO₂ environment (blue arrow); C: The bacterial morphology of E. corrodens with a direct smear of E. corrodens colonies in culture (blue arrow).

The sample was cultured on sheep blood agar plates and incubated at a temperature range of 35 °C-37 °C in a CO₂-enriched environment. After 24 h, pinpoint-sized colonies were observed on the blood agar plates. Continuing the culture for an additional 24 h revealed the characteristic colony morphology of this bacterium, which exhibited a dry, flat appearance with a centrally raised, radiating structure resembling either a mushroom or helmet shape. Prolonged incubation led to the development of greenish discoloration surrounding the colonies, while gentle scraping with a cotton swab resulted in light yellow coloration. Pure cultures of this bacterium emitted an unmistakable odor reminiscent of fungal oral flora (Figure 2B)[8]. Under microscopic observation (Figure 2C), numerous red and straight Gram-negative bacteria were detected.

When pathogen biochemical tests of E. corrodens were taken, the E. corrodens strain exhibited negative results for catalase, urease, arginine hydrolase, and indole examinations[9]. However, the typical isolates demonstrated positive outcomes for ornithine decarboxylase and nitrate reduction tests, as well as lysine decarboxylase and oxidase detections (Figure 3), despite their inability to ferment sugars in a medium without additives.

Figure 3 Display of biochemical reaction of Eikenella corrodens colonies in culture. The typical isolates demonstrated positive outcomes for ornithine decarboxylase (the far left) and nitrate reduction tests (the left of the middle), as well as lysine decarboxylase (the right of the middle), and oxidase detections (the far right).

As suggested by the infectiologist, empiric intravenous antibiotic treatment was started with imipenem cilastatin sodium (1 g every 6 h)[8], and meropenem (2 g every 8 h) was performed for more than 10 d after confirming infection of E. corrodens. While the patient started to worsen 18 d after antibiotic therapy, and then vancomycin (2 g/d) was added, and continued the antibiotic treatment until discharge with death.

FINAL DIAGNOSIS

Combined with the patient’s medical history, the final diagnosis was empyema.

TREATMENT

The patient died on day 22 in hospital. After the diagnosis of empyema, the patient received antimicrobial therapy until his death.

OUTCOME AND FOLLOW-UP

On day 22 after admission, the patient died.

DISCUSSION

E. corrodens, a member of the HACEK group and part of the commensal flora on human mucosal surfaces is frequently isolated from upper respiratory tract specimens and can also be found in gastrointestinal or urogenital specimens as well as those associated with animal bite infections[10,11]. However, it typically exhibits non-pathogenic behavior when the immune defense system is normal. In situations where the body’s immune defense system is compromised or there is mucosal damage, E. corrodens can invade surrounding tissues and cause severe infections.

In this case report, when compared to the articles in the literature, the reports of E. corrodens invading the pleural cavity were not many, only 8 cases and most of they were non-spontaneous and sole pathogen bacterial, two cases with forming a draining sinus were confirmed and 6 ones were unknown because of the time of publication was too early, as shown in the Table 1. So, our case report was valuable enough.

This type of case report of E. corrodens invading the pleural cavity was rare may be for reason that detecting and culturing this bacterium presents a challenge due to its high nutritional requirements and facultative anaerobic nature that thrives in environments containing 5% to 10% CO₂ and hemin-containing media. Therefore, the bacterium exhibits a slow growth rate, typically requiring 48-72 h for the development of characteristic colonies. In the course of laboratory work, it is often disregarded due to inadequate incubation time[1,8] and its classification as a contaminant. Consequently, the clinical examination and analysis of this bacterium face certain challenges, particularly in basic hospitals within China. Thus, extending the culture duration or improving culture conditions has the potential to facilitate pathogen isolation and identification, thereby enhancing patient care and rehabilitation.

Furthermore, meticulous consideration should be given to the selection of an appropriate specimen type, prioritizing samples collected from sterile sites, and strictly adhering to aseptic procedures during the sample collection. Moreover, timely clinical communication is indispensable for prompt reporting of identification results and providing empirical guidance for medication, particularly after culturing E. corrodens in sterile specimens where microbiology staff should immediately notify clinics about bacterial characteristics and drug recommendations.

The CLSI M45-A2 guidelines offer a comprehensive range of information on antimicrobial susceptibility. Preferred antimicrobial agents for E. corrodens include ampicillin-sulbactam, amoxicillin/clavulanic acid, cefotaxime, cefepime, imipenem, penicillin, and other options. Certain strains of E. corrodens may exhibit resistance to clindamycin and produce beta-lactamases that can be inhibited by enzyme inhibitors. Ampicillin-sulbactam or third-generation cephalosporins are recommended for soft tissue infections while third-generation cephalosporins are the optimal choice for infective endocarditis[1,12,13].

Despite the formidable challenges associated with conducting drug susceptibility testing for E. corrodens under its highly demanding culture conditions, we diligently adhere to the guidelines outlined by CLSI-M45 in our earnest endeavors to perform such assessments. In cases where trial or failure arises during drug sensitivity evaluations, it becomes imperative to actively consult relevant literature sources for extracting valuable insights, engage in effective communication with clinical personnel, and submit a comprehensive treatment proposal. Although the range of antibacterial drugs tested may be limited, they can still serve as invaluable tools for guiding clinical treatment and management.

Fortunately, with the advancement of microbiological detecting techniques, mass spectrometry technology, and molecular biological methods can be utilized for rapid and accurate identification of bacteria. It’s just there is an uneven distribution of construction and diagnostic capacity among the microbiology laboratories of the basic hospitals, resulting in insufficient identification capabilities for rare or difficult-to-identify bacteria as well as certain pathogenic bacteria causing special infections, and leading to delayed clinical treatment or inappropriate management. Therefore, it is crucial to strengthen the establishment of basic laboratories, enhance the diagnostic abilities of grassroots laboratories, and improve the professional competence of staff[14].

CONCLUSION

In summary, our case revealed its difficulties in detecting distinctive characteristics, as well as a detection model worth promoting. E. corrodens, a rare bacterium in the HACEK group, possesses the potential to induce infections across diverse anatomical sites. When it is identified as the sole pathogen causing pleural effusion infection, it should be regarded with utmost seriousness. In clinical laboratory practice, prioritizing attention towards less common bacteria such as Actinobacillus or Streptobacillus species within the HACEK group is crucial[15]. By extending culture time and enhancing culture conditions to improve the isolation and identification of pathogens, detection rates can be significantly augmented. For laboratories, expediting and accurately identifying pathogens plays a pivotal role in optimizing patient treatment outcomes.

ACKNOWLEDGEMENTS

We thank doctors for the provision of clinical data.