Corynebacterium aurimucosum is a bacterial species within the large Corynebacterium genus, a group that includes both harmless environmental organisms and significant human pathogens. First described in 2002, this microorganism has steadily gained recognition in clinical settings as molecular identification techniques have improved. The species is increasingly understood to be an opportunistic pathogen, particularly in vulnerable patient populations. This article explores the organism’s taxonomic identity, genomic insights, and its growing importance in human health and therapeutic management.
Classification and Habitat
Corynebacterium aurimucosum belongs to the phylum Actinomycetota and the family Corynebacteriaceae. It is a Gram-positive, non-motile, rod-shaped bacterium that often exhibits pleomorphic or club-shaped (coryneform) morphology. It is a facultative anaerobe, meaning it can grow in both the presence and absence of oxygen.
The organism is a common member of the normal human microbial flora, primarily colonizing the skin and mucosal surfaces. It is frequently isolated from the female urogenital tract, the respiratory tract, and the gut. Historically, a black-pigmented variant of this species was misclassified as Corynebacterium nigricans, but subsequent genetic analysis confirmed it to be the same species.
The discovery of C. aurimucosum helped clarify the taxonomy of a previously heterogeneous group of bacteria. Before its formal classification, the organism was often misidentified or grouped with its closest phylogenetic neighbor, Corynebacterium minutissimum, due to similar biochemical profiles.
Genomic Analysis and Identification
Accurate identification of C. aurimucosum relies on advanced molecular and proteomic techniques, as traditional biochemical tests often fail to distinguish it from other commensal corynebacteria. Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) provides rapid identification by matching the organism’s protein profile against an extensive database. However, 16S rRNA gene sequencing remains the gold standard for definitive species assignment.
Whole-Genome Sequencing (WGS) provides specific insights into the organism’s lifestyle and pathogenic potential. The genome includes a circular chromosome, approximately 2.79 million base pairs, and a plasmid (pET44827) in certain strains. This plasmid carries a gene cluster responsible for synthesizing a non-ribosomal peptide synthetase.
This synthetase produces the black pigment observed in the historical C. nigricans variant. The pigment is thought to be an adaptation mechanism, protecting the bacteria from the high hydrogen peroxide concentrations found in the vaginal environment. WGS data also reveals metabolic flexibility, showing gene sets that facilitate the degradation of various compounds like aromatic amines and L-tartrate, enabling the organism to thrive in diverse human niches.
Genomic comparison confirms that while C. aurimucosum is phylogenetically close to C. minutissimum, the two are distinct species. This distinction is based on crucial differences observed through DNA-DNA hybridization experiments.
Clinical Manifestations
As an opportunistic pathogen, C. aurimucosum primarily causes infections in individuals with underlying health conditions, compromised immune systems, or those with implanted medical devices. Its ability to adhere to surfaces and form biofilms is a significant factor in device-related infections. The organism is one of the most frequently isolated non-diphtherial corynebacteria from clinical specimens.
Infections are diverse, frequently including prosthetic joint and bone infections, which often require both surgical intervention and prolonged antimicrobial therapy. The organism also frequently causes urinary tract infections (UTIs) and bloodstream infections (bacteremia).
Specific manifestations include superficial skin infections, such as erythrasma, where the organism produces coproporphyrin III, leading to a characteristic coral-red fluorescence under Wood’s light. Furthermore, the black-pigmented strains isolated from the female urogenital tract have been associated with complications during pregnancy, including septic abortion. The clinical picture is often complicated by the fact that C. aurimucosum is sometimes isolated alongside other bacteria in polymicrobial infections, especially in skin and soft-tissue sites.
The presence of indwelling foreign bodies, such as central venous catheters or prosthetic implants, significantly increases the risk of symptomatic infection. Given its status as a common commensal, determining if an isolate is a true pathogen or merely a contaminant requires careful clinical correlation, especially when isolated from non-sterile sites like skin swabs.
Antibiotic Susceptibility Patterns
The treatment of C. aurimucosum infections is complicated by a variable antibiotic susceptibility profile, making individualized testing necessary for clinical management. Standardized susceptibility testing reveals that the organism is consistently susceptible to certain agents, providing reliable options for serious infections. Specifically, vancomycin and linezolid show near-universal efficacy against tested isolates.
Conversely, the species exhibits frequent resistance to several common antibiotic classes. Over 90% of isolates are typically resistant to penicillin G and clindamycin. This resistance is often attributed to the production of enzymes that inactivate or modify the drug, such as beta-lactamases for penicillin.
Susceptibility to other antibiotics varies considerably between strains. While a majority of isolates may be susceptible to agents like amoxicillin, gentamicin, tetracycline, and rifampicin, treatment with ciprofloxacin or cefotaxime can be unreliable, with only about 50% of strains showing susceptibility.
Because of this mixed susceptibility pattern, empirical therapy should be chosen with caution, favoring agents known to be consistently effective, such as vancomycin, until laboratory results from the patient’s specific isolate are available. The prevalence of resistance to beta-lactams and fluoroquinolones means these drugs should generally be avoided as first-line, empirical treatment for suspected C. aurimucosum infections.