Acinetobacter ursingii: Introduction, Morphology, Pathogenicity, Lab

Introduction

Table of Contents

Acinetobacter ursingii is a Gram-negative, non-fermentative, opportunistic bacterium belonging to the genus Acinetobacter. It is an uncommon species compared to Acinetobacter baumannii, but it has been increasingly recognized in healthcare-associated infections (HAIs). Reported cases include bacteremia, septicemia, pneumonia, urinary tract infections, and bloodstream infections, particularly in immunocompromised or hospitalized patients.

Morphology

Fig. Acinetobacter ursingii growth on blood agar

Gram Stain: Gram-negative coccobacilli, often appearing as short rods.
Growth on Media:
- Grows well on blood agar and MacConkey agar.
- Colonies: smooth, opaque, circular, and non-pigmented.
Motility: Non-motile.
Biochemical Features:
- Oxidase negative, catalase positive.
- Non-fermenter, utilizes limited carbon sources.

Fig. Acinetobacter ursingii on MacConkey agar

Pathogenicity

Acts as an opportunistic pathogen, causing disease in patients with underlying conditions or indwelling devices.
Clinical Manifestations:
- Bacteremia/septicemia (most common).
- Pneumonia (especially ventilator-associated).
- Urinary tract infections.
- Wound and catheter-associated infections.
Produces biofilms, enhancing persistence in hospital environments and on medical devices.
Emerging reports of multidrug resistance complicate management.

Laboratory Diagnosis

Numerous pink to red-stained bacilli , arranged in short rods and elongated chains of Acinetobacter ursingii while some appear slightly curved, while others in clusters or dispersed individually — Fig. Numerous pink to red-stained bacilli, arranged in short rods and elongated chains of Acinetobacter ursingii, while some appear slightly curved, while others are in clusters or dispersed individually

Specimen Collection: Blood, sputum, urine, wound swabs, catheter tips.
Culture: Growth on blood agar, MacConkey agar. Colonies may resemble other Acinetobacter spp.
Identification:
- Conventional biochemical testing may misidentify the species.
- Accurate identification requires MALDI-TOF MS or molecular sequencing (16S rRNA, rpoB gene).
Antimicrobial Susceptibility Testing (AST): Performed by CLSI/EUCAST broth microdilution or automated systems.

Acinetobacter ursingii in Gram staining — Fig. Acinetobacter ursingii in Gram stain

Treatment

Most strains are susceptible to a wider range of antibiotics than A. baumannii, but resistance is increasing.
Therapeutic options:
- Beta-lactams (piperacillin-tazobactam, cephalosporins, carbapenems in some cases).
- Fluoroquinolones, aminoglycosides, tetracyclines.
Multidrug-resistant isolates: May require colistin or combination therapy.
Therapy should always be guided by susceptibility testing.

Fig. Acinetobacter ursingii in Gram staining at a magnification of 4000X

Gram negative cocobacilli to Gram negative rods of Acinetobacter ursingii in Gram staining of culture microscopy at a magnification of 4000X — Fig. Gram-negative cocobacilli to Gram-negative rods of Acinetobacter ursingii in Gram staining of culture microscopy at a magnification of 4000X

Acinetobacter ursingii in Gram staining of culture — Fig. Acinetobacter ursingii in a Gram stain of culture

Prevention

Fig. Acinetobacter ursingii in Gram staining of culture microscopy at a magnification of 4000X

Infection control measures in hospitals (hand hygiene, device care, surface disinfection).
Judicious antibiotic use to prevent resistance selection.
Active surveillance in ICUs and oncology wards.
Strict sterilization of indwelling medical devices.

Keynotes

Gram negative coccobacilli to large Gram negative rods of Acinetobacter ursingii in Gram staining of culture — Fig. Gram negative coccobacilli to large Gram-negative rods of Acinetobacter ursingii in Gram staining of culture

Acinetobacter ursingii is a rare but emerging opportunistic pathogen in hospital settings.
Causes primarily bloodstream and device-associated infections in immunocompromised patients.
Often misidentified without molecular or MALDI-TOF confirmation.
Treatment outcomes are generally better than for A. baumannii, but resistance is rising.
Strong infection prevention practices are essential to reduce transmission.

Acinetobacter ursingii: Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynote