Acinetobacter lwoffii: Introduction, Pathogenicity, Lab Diagnosis

Introduction

Table of Contents

Acinetobacter lwoffii is a Gram-negative, strictly aerobic, non-motile, non-fermenting, and oxidase-negative bacterium. It belongs to the genus Acinetobacter within the family Moraxellaceae. Unlike its highly aggressive relative Acinetobacter baumannii, A. lwoffii is generally considered a commensal organism. It regularly lives as normal flora on human skin (found in about 25% of healthy individuals), the oropharynx, and the perineum

Acinetobacter lwoffii colony morphology on CLED agar — Fig. *Acinetobacter lwoffii* colony morphology on CLED agar

It is ubiquitous in the environment, thriving in soil, water, plants, and various foodstuffs like raw poultry. However, it is a significant opportunistic nosocomial (hospital-acquired) pathogen. It possesses a unique ability to survive desiccation (drying out) on clinical surfaces, medical devices, and human hands for extended periods.

Pathogenicity & Clinical Manifestations

While A. lwoffii is a low-virulence organism in healthy populations, it acts as a dangerous opportunistic pathogen in immunocompromised individuals or patients in intensive care units (ICUs).

Virulence Factors

Cell-surface hydrophobicity: Helps the bacteria adhere tightly to plastics (like catheters) and human tissues.
Slime polysaccharides (Biofilms): Protect the bacteria against host neutrophils and immune clearance.
Outer membrane proteins (OMPs): Play a key role in inducing apoptosis in host epithelial cells.
Siderophores: Allow the bacteria to scavenge iron from the host to survive and replicate.

Risk Factors

Infection risks escalate drastically for individuals with underlying conditions, including:

Prolonged hospital stays or ICU admission.
Indwelling medical devices (e.g., central venous catheters, urinary catheters, endotracheal tubes).
Disrupted skin barriers (surgical wounds, severe burns, or trauma).
Chronic illnesses (diabetes, alcoholism, chronic lung disease).

Associated Infections

Bloodstream Infections (Bacteremia/Septicemia): Frequently associated with contaminated intravenous lines. It can quickly turn severe if the bacteria gain access to the circulatory system.
Pneumonia: Particularly ventilator-associated pneumonia (VAP) in intubated patients.
Urinary Tract Infections (UTIs): Typically linked to prolonged urinary catheterization.
Meningitis: Rare, but can occur following neurosurgical procedures or head trauma.
Skin and Wound Infections: Ranging from mild cellulitis to aggressive necrotizing soft-tissue infections

Laboratory Diagnosis

Accurate identification is required to distinguish A. lwoffii from other Gram-negative non-fermenters and to guide targeted therapy.

Clinical Specimen Collection ───►Blood, Sputum, Urine, Wound

Gram Staining ───► Plump Gram-negative coccobacilli / diplococci

Culture on Agar───► Blood Agar (non-hemolytic, opaque colonies)

───► MacConkey Agar (pale, non-lactose fermenting)

Biochemical Testing ──► Oxidase (-), Catalase (+), Motility (-), non-fermentative

Automated / Advanced ──► MALDI-TOF MS, VITEK 2, or 16S rRNA Sequencing

Acinetobacter lwoffii on CLED medium — Fig. *Acinetobacter lwoffii* on CLED medium

Microscopy (Gram Stain): Appears as Gram-negative coccobacilli. They are typically short, plump, and arranged in pairs (diplococci), which can sometimes cause them to be mistaken for Neisseria species.
Cultural Characteristics:
- Blood Agar: Grows well at 35°C–37°C, forming smooth, opaque, greyish-white, non-hemolytic colonies.
- MacConkey Agar: Forms pale, colorless, or faintly pink colonies because it is a non-lactose fermenter.
Biochemical Profile:
- Oxidase test: Negative (critical for differentiating it from Pseudomonas).
- Catalase test: Positive.
- Motility: Non-motile.
- Sugar Fermentation: Strictly oxidative or non-reactive; it does not ferment glucose or lactose.
Advanced Methods: Automated systems like VITEK 2, MALDI-TOF mass spectrometry, or 16S rRNA gene sequencing are standard in modern laboratories for precise species-level identification.

Treatment

Historically, A. lwoffii has shown a lower capacity to accumulate resistance genes compared to A. baumannii. However, modern clinical isolates are increasingly demonstrating multidrug resistance (MDR). Antimicrobial Susceptibility Testing (AST) must always be performed to choose the proper regimen.

Standard Treatment Options

Carbapenems: Meropenem or Imipenem remain highly effective first-line agents against susceptible strains.
Sulbactam Combinations: High-dose Ampicillin-sulbactam. The sulbactam portion possesses unique, direct bactericidal activity against Acinetobacter species.
Extended-Spectrum Cephalosporins: Cefepime or Ceftazidime.
Fluoroquinolones & Aminoglycosides: Ciprofloxacin, Levofloxacin, or Amikacin are often utilized based on susceptibility profiles.

fAcinetobacter lwoffii on CLED agar showing smooth, mucoid, and glistening circular bluish colonies — Fig. Acinetobacter lwoffii on CLED agar showing smooth, mucoid, and glistening circular bluish colonies

Treatment for Resistant (MDR/Carbapenem-Resistant) Strains

Polymyxins: Colistin (Polymyxin E) or Polymyxin B serve as vital backbone salvage therapies for highly resistant infections.
Tetracycline Derivatives: Tigecycline or Minocycline.
Novel Combinations: Sulbactam-durlobactam (a specialized beta-lactamase inhibitor combo engineered specifically to combat resistant Acinetobacter).

Prevention and Control

Because A. lwoffii easily contaminates the hospital environment and resists standard desiccation, rigorous infection control is mandatory.

Strict Hand Hygiene: Healthcare providers and caregivers must clean their hands thoroughly using alcohol-based hand rubs or soap and water before and after touching patients or medical equipment.
Environmental Disinfection: Thorough, daily cleaning of hospital rooms, ICU surfaces, and patient care items (such as keyboards, ventilators, and bedside tables). Note that Acinetobacter can sometimes resist low concentrations of chlorhexidine or phenols; hence, use of approved hospital-grade disinfectants at correct concentrations is critical.
Device Care & Management: Prompt removal of indwelling devices (urinary catheters, central lines) as soon as they are no longer clinically necessary.
Contact Isolation Precautions: Grouping or isolating patients colonized or infected with MDR Acinetobacter strains to prevent horizontal transmission via staff hands or equipment.
Antimicrobial Stewardship: Restricting the unnecessary use of broad-spectrum antibiotics to limit the selective pressure that generates multi-drug resistant strains.

Keynotes

Commensal Turned Pathogen: Naturally colonizes the human skin and upper respiratory tract in up to a quarter of healthy populations but turns dangerous inside ICUs.

Smooth, mucoid, and glistening circular bluish colonies of Acinetobacter lwoffii on CLED agar — Fig. Smooth, mucoid, and glistening circular bluish colonies of *Acinetobacter lwoffii* on CLED agar

Environmental Survivalist: Possesses an exceptional capacity to resist drying out (desiccation), enabling it to survive on dry hospital surfaces, linens, and medical hardware for days to weeks.
Morphological Mimic: Gram-negative coccobacilli that often look like diplococci under the microscope, occasionally mimicking Neisseria.
Key Lab Signatures: Differentiated from other non-fermenting rods (like Pseudomonas) by being completely oxidase-negative and non-motile.
Resistance Trend: Generally less resistant than A. baumannii, but clinical isolates are progressively showing increased resistance to standard beta-lactams, making susceptibility testing essential.

Acinetobacter lwoffii: Introduction, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes