Subcutaneous Eikenella corrodens, Actinomyces sp., and α-Hemolytic Streptococcus Abscess of the Thigh following a Vitamin B12 Injection

This case report describes a 38-year-old female presenting with a thigh abscess caused by Eikenella corrodens, Actinomyces sp., and α-hemolytic Streptococcus following an intramuscular vitamin B12 injection administered at an outpatient clinic. After failure to improve clinically with intravenous daptomycin and after visualization of the abscess with gas bubbles on CT scan, she was taken to the operating room for three separate surgical irrigation and debridement procedures. Treatment also included intravenous ampicillin/sulbactam followed by oral amoxicillin/clavulanic acid therapy. She remained symptom free and without infection at nine months following hospitalization. It was suspected that poor hygiene played a role in the infection, but a definitive cause was not identified.

Oxygen as a Virulence Determinant in Polymicrobial Infections

ABSTRACT Infections caused by multiple organisms, or polymicrobial infections, are likely more common than is broadly appreciated. Interaction among microbial communities (and with their host) can change the infection landscape by subverting immunity, providing nutrients and inhibiting competing microbes. Stacy et al. (A. Stacy, D. Fleming, R. J. Lamont, K. P. Rumbaugh, and M. Whiteley, mBio 7:e00782-16, 2016, http://dx.doi.org/10.1128/mBio.00782-16 ) described a novel mechanism that results in synergistic growth of oral microbes Aggregatibacter actinomycetemcomitans and Streptococcus gordonii . The authors used whole-genome fitness profiling by transposon sequencing (Tn-seq) to identify genes differentially required for growth in vitro versus in a mono- or coinfection in a thigh abscess model. They found that coinfection with S. gordonii allowed A. actinomycetemcomitans to shift from an anaerobic to an aerobic mode of growth. This shift involved the production of a terminal electron acceptor H 2 O 2 by S. gordonii and increased A. actinomycetemcomitans persistence—an interaction termed “cross-respiration.”