Eikenella corrodens in head and neck infections

Summary

Background

Eikenella corrodens (E. corrodens) is a Gram-negative facultative anaerobic bacillus that originally was thought to be an attenuated and indigenous bacterium. In recent years, a number of reports have documented that E. corrodens can be a potential pathogen not only in immunocompromised patients but also in hosts with normal immunity. We herein study E. corrodens infections of the head and neck encountered in our department.

Methods

Twenty-two consecutive patients treated in our department for E. corrodens infections of the head and neck were retrospectively analyzed. Microbial specimens were subjected to light microscopic examination, aerobic culture using chocolate and sheep blood agar media, and anaerobic culture using Brucella HK agar medium. Cultured bacteria were subjected to antimicrobial susceptibility tests by means of the broth microdilution method.

Results

There were 16 males and 6 females with an average age of 29.9 years. Two patients had malignancy, while the other patients had no particular risk factors or underlying diseases. Infected sites were the ear in 6 cases, pharynx in 12 cases (tonsil in 10 cases), paranasal sinuses in 3 cases, and salivary gland in 1 case. Seventeen patients suffered polymicrobial infections. Staphylococcus and Streptococcus were the most frequently detected pathogens coexisting with E. corrodens, and mixed infections of E. corrodens and Streptococcus milleri group bacteria were prone to form abscesses. Isolated E. corrodens was susceptible to third-generation cephems (MIC90 = 0.15–0.25 μg/ml), carbapenems (MIC90 ≦ 0.15 μg/ml), and new quinolones (MIC90 ≦ 0.15 μg/ml), and resistant to oxacillin (MIC90 > 8 μg/ml), cefazolin (MIC90 > 4 μg/ml), macrolides (MIC90 = 4–8 μg/ml), and clindamycin (MIC90 > 4 μg/ml).

Conclusions

E. corrodens infections of the head and neck occur most frequently in the tonsil even in hosts with normal immunity. Coexistence with Streptococcus milleri group bacteria and the use of ineffective antibiotics can be exacerbating factors. First-choice drugs for E. corrodens infections should be third-generation cephems, carbapenems, or new quinolones.

Introduction

Eikenella corrodens (E. corrodens) is a Gram-negative facultative anaerobic bacillus¹ that was first isolated by Eiken in 1958 from human saliva.² In primary culture, E. corrodens grows under anaerobic conditions only, but survives in aerobic conditions after subcultivation.¹ This bacterium absolutely requires 5–10% of carbon dioxide at the beginning of primary culture, and hemin must be supplemented for it to grow under aerobic conditions.³ Moreover, it takes several days for E. corrodens to form macroscopic colonies, which are generally small in size and are often hidden by colonies of other organisms.³ E. corrodens is, therefore, usually overlooked during routine bacteriological examinations, and special laboratory precautions and techniques are necessary to isolate this bacterium.⁴

E. corrodens was originally thought to be an attenuated and indigenous bacterium in the human oral cavity, gastrointestinal tract, genitalia, etc.,⁵ and did not arouse much interest until the 1960s. However, since the 1970s, a number of reports have documented that E. corrodens can be a potential pathogen of various infective diseases not only in immunocompromised patients but also in hosts with normal immunity.6, 7, 8 It is also interesting that E. corrodens enhances the virulence of coexisting bacteria such as Streptococcus species in experimental animals.9, 10

Although there are sporadic case reports describing E. corrodens infections of the head and neck, systematic analysis of the significance of this pathogen in the field of otorhinolaryngology has not been performed yet. Here, we present 22 cases with E. corrodens infections encountered in our department during the past 7 years, and summarize their clinical characteristics and potential problems upon treatment.