Actinotignum schaalii

Background

Microbiology

• Small, non-motile, non-spore forming, facultatively anaerobic Gram-positive slightly curved bacillus to coccobacillus within the genus Actinotignum
• Fastidious, growing slowly on blood agar
• Previously known as Actinobaculum schaalii
• Classified within the family Actinomycetaceae, which also includes Arcanobacterium and Trueperella
• Member of the genitourinary microflora

Epidemiology

• Occurs most often in patients older than 60 years or in children
• May be more common in patients with preexisting genitourinary conditions, including bladder cancer, urinary incontinence, urinary catheterization, BPH, neurogenic bladder, urethral stenosis, and prostate cancer, as well as in immunocompromised hosts

Clinical Manifestations

• Rare, with only a few hundred cases described to date1
• Mostly causes urinary tract infection (70% of cases published by 2016), which includes cystitis or prostatitis (40%), urosepsis or pyelonephritis (29%), epididymitis (0.5%), and bladder necrosis (0.5%)
• Also causes bacteremia (19%), abscesses mostly in the groin but also elsewhere (7%), cellulitis (1.5%), discitis (1.5%), endocarditis (0.5%), and Fournier gangrene (0.5%)

Management

• Susceptible to all β-lactams, as well as tetracyclines, vancomycin, linezolid, rifampin, and nitrofurantoin
• May be susceptible to fosfomycin
• Can have reduced susceptibility to gentamicin and can be resistant to macrolides, lincosamides, TMP-SMX, and ciprofloxacin (though may be susceptible to levofloxacin and moxifloxacin)

Further Reading

• Actinotignum schaalii (formerly Actinobaculum schaalii): a newly recognized pathogen—review of the literature. Clin Microbiol Infect. 2016;22(1):28-36. doi: 10.1016/j.cmi.2015.10.038
• Clinical and microbiological features of Actinotignum bacteremia: a retrospective observational study of 57 cases. Eur J Clin Microbiol Infect Dis. 2017;36(5):791–796. doi: 10.1007/s10096-016-2862-y