Actinotignum schaalii

an emerging pathogen

Actinotignum schaalii

Actinotignum schaalii is a commensal bacteria of the human urinary tract, female genital tract and skin, especially the groin area. It is a considered an emerging pathogen primarily known to cause infection of the urinary tract.

It was first discovered in 1997, but it was previously called Actinobaculum schaalii.
In 2015, the genus Actinobaculum was divided into two genera
1. Actinotignum, which contains Actinotignum schaalii and
2. Actinobaculum, including Actinobaculum suis.

Actinotignum schaalii infection

Urinary tract infection

Actinotignum schaalii is most commonly associated with urinary tract infection, especially in older people. However, cases from children have been reported as well.

Actinotignum UTI is usually associated with immunosuppression and urological abnormalities like bladder cancer, prostate cancer, neurological bladder, benign hypertrophy of the prostate, urethral stricture, catheterization, etcetera.

Other infection

Other infection reported in the literature are - bacteraemia, abscess, Fournier’s gangrene, endocarditis, cellulitis and discitis.

Actinotignum schaalii laboratory identification

Actinotignum schaalii gram stain

Actinotignum schaalii gram stain

Actinotignum schaalii gram stain
(pic Manurx27, Wikipedia)

It is a thin Gram-positive rod, often slightly curved.

Actinotignum schaalii culture

Actinotignum schaalii colony

Actinotignum schaalii colony (Wikimedia, Manurx27)

It is a facultative anaerobe.

It produces non-haemolytic or weakly alpha haemolytic colonies on the blood agar.

It is also a slow-growing organism. Most laboratories in the UK culture the urine on a chromogenic agar and incubate it for 24 hours only. This may result in failure to grow this bacteria.

Identification

  • This bacteria is CAMP, catalase, and oxidase negative.

  • It is also negative for nitrate reduction. So it will not give a nitrate positive reaction on the dipstick test when it causes UTI.

  • It can be identified using 16S rRNA and MALDI ToF technology.

  • Commercial systems are known to misidentify it as Gardnerella, Arcanobacterium or Actinomyces.

Actinotignum schaalii treatment

It is usually sensitive to beta-lactam antibiotics (except mecillinam).
It is also sensitive to doxycycline, vancomycin, teicoplanin, linezolid, rifampicin, nitrofurantoin, gentamicin and 3rd and 4th generation quinolones like levofloxacin and moxifloxacin.

2nd generation quinolones like ciprofloxacin should not be used as it is mostly resistant. Another antibiotic to which this bacteria is consistently resistant is cotrimoxazole.

Variable resistance had been reported to mecillinam, Fosfomycin, macrolides and clindamycin.

There is no guideline for treatment; hence specialist opinion should be taken as it is crucial to consider pharmacokinetics and the pharmacodynamics of the antibiotics depending on the site of infection.