Case report of an abdominal wet gangrene caused by Acidaminococcus

The Acidaminococcus genus is a part of the normal flora in gastrointestinal tract. It is a strictly anaerob Gram-negative coccus that is rarely pathogenic. We report the case of a 58-year-old man, who presented to surgery department A of the Charles Nicolle hospital, complaining of a wide inflammatory lesion in the anterior abdominal wall evolving for two weeks. Patient's anamnestic data included smoking, hypertension, and diabetes mellitus with poor compliance. The patient underwent flattening with excision of necrotic tissues and surgical drainage using a DELBET blade. Empirical antibiotic therapy with imipenem 1gx3/d, teicoplanin 400 mg 1 inj x2/d and gentamicin 400 mg 1 inj/d was administered pending bacteriological results. The bacteriological examination of a sample of necrotic tissue, after 72 h of incubation at 37 °C in anaerobic atmosphere, was able to detect a Gram-negative coccus, that the VITEK2 ANC system identified as Actinomyces canis with an accuracy of 80%. Whole genome sequencing was subsequently performed, that identified Acidaminococcus sp. AM33-14BH and demonstrated the following resistance genes: cfxa, tet(X) and tet(Q). An antibiogram for anaerobes was performed showing that the strain was resistant to amoxicillin but sensitive to amoxicillin-clavulanic acid, piperacillin-tazobactam, ertapenem, imipenem, meropenem and rifampin. Patient's condition improved after treatment with imipenem for 2 weeks, followed by oral amoxicillin-clavulanic acid for 16 days.This work highlights the role of molecular biology in the diagnosis of infections caused by anaerobes. Although the Vitek 2 ANC card provides rapid and acceptable identification of the most common anaerobic bacteria, improvements are needed for the identification of bacteria in the genera Acidaminococcus and Actinomyces.