Acinetobacter haemolyticus-Introduction, Morphology, Pathogen

Introduction

Table of Contents

Acinetobacter haemolyticus is an aerobic, non-fermenting bacterium found in nature and hospital environments. It belongs to the Acinetobacter genus, frequently causing healthcare-associated infections. It is generally considered less virulent than Acinetobacter baumannii but is increasingly recognized in human infections.

Morphology

Shape: Gram-negative coccobacilli
Arrangement: Pairs or short chains
Staining: Gram-negative
Motility: Non-motile
Colony Characteristics: Smooth, white to cream colonies on blood agar. It typically displays beta-hemolysis on blood agar, distinguishing it from non-hemolytic species.

Pathogenicity

Opportunistic Nature: Primarily affects immunocompromised patients or those with invasive devices (ventilators, catheters).
Infection Sites: It causes pneumonia (often ventilator-associated), bloodstream infections (BSIs), and infections in surgical or burn wounds.
Virulence Factors: Adhesins (fimbriae) for attaching to surfaces and host cells, iron-acquisition systems, and the ability to form biofilms on medical equipment.
Environmental Survival: Highly resilient; can survive for long periods in hospitals, contributing to persistent outbreaks.

Lab Diagnosis

Specimens: The common specimens are blood, urine, sputum, and wound swabs.
Gram Stain: Direct microscopic observation of Gram-negative coccobacilli.
Culture: Grows readily on blood agar (showing hemolytic colonies) and MacConkey agar (non-lactose fermenting).

Fig. Acinetobacter haemolyticus growth on CLED agar

Biochemical Tests: Oxidase-negative, catalase-positive, non-motile.
Identification: Automated systems (e.g., VITEK 2 compact) or Matrix-Assisted Laser Desorption/Ionization-Time of Flight (MALDI-TOF) mass spectrometry (VITEK-MS).

Treatment

Multidrug Resistance: Acinetobacter species, including Acinetobacter haemolyticus, are frequently resistant to multiple antibiotics.
Treatment Options: Therapy is based on susceptibility testing, with carbapenems (meropenem, imipenem) commonly used, although resistance is rising.
Alternative Agents: Colistin and tigecycline may be utilized for multidrug-resistant strains.

Prevention

Infection Control: Strict adherence to hand hygiene by healthcare staff is critical.
Environmental Cleaning: Enhanced cleaning and disinfection of patient rooms and equipment to eliminate environmental reservoirs.
Infection Control Practices: Use of transmission-based precautions (wearing gloves or gowns) and cohorting patients with known infections.

Keynotes

Acinetobacter haemolyticus is known for causing beta-hemolysis (hemolytic activity on blood agar).
High resilience allows it to persist on dry surfaces.
It is an increasingly important, yet sometimes overlooked, pathogen in nosocomial, especially ventilator-associated pneumonia (VAP).
A major issue in treatment is the increasing emergence of carbapenem resistance.

Acinetobacter haemolyticus-Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes