Acinetobacter baumannii-Introduction, Morphology, Pathogenicity

Introduction

Table of Contents

Fig. Acinetobacter baumannii in Gram staining of sputum

Acinetobacter baumannii is a Gram-negative, non-fermenting, aerobic coccobacillus. It is an opportunistic pathogen increasingly associated with nosocomial infections, particularly in critically ill or immunocompromised patients. Notorious for its antibiotic resistance, it has become a major global health concern, particularly in ICU settings.

Morphology

Gram-negative coccobacilli, often appearing in pairs
Non-motile, oxidase-negative, and catalase-positive
Appears as smooth, opaque, creamy colonies on blood agar
Non-lactose fermenting on MacConkey agar
Survives for long periods on surfaces due to desiccation resistance

Fig. Acinetobacter baumannii in wet mount of culture microscopy

Pathogenicity

Causes ventilator-associated pneumonia (VAP), bloodstream infections (BSI), meningitis, wound infections, and urinary tract infections (UTIs)
Produces biofilms, contributing to device-related infections
Secretes enzymes such as β-lactamases and has efflux pumps
Known for horizontal gene transfer, contributing to multidrug resistance (MDR)
Targets include patients with catheters, ventilators, open wounds, or prolonged antibiotic exposure

Laboratory Diagnosis

Specimens: Sputum, blood, CSF, urine, wound swabs
Culture characteristics:
- Growth on blood agar and MacConkey agar (non-lactose fermenter)
Microscopy: Gram stain shows Gram-negative coccobacilli
Biochemical tests:
- Oxidase-negative
- Non-fermenter in oxidative-fermentative media
Advanced ID methods:
- MALDI-TOF MS, VITEK, or PCR for species confirmation
Antimicrobial susceptibility testing (AST):
- Essential due to frequent MDR/XDR profiles

Gram negative coccobacilli of Acinetobacter baumannii in Gram staining of culture — Fig. Gram-negative coccobacilli of Acinetobacter baumannii in Gram staining of culture

Treatment

Empirical therapy should be guided by the local antibiogram
MDR strains are often resistant to carbapenems, cephalosporins, and aminoglycosides
Commonly used antibiotics:
- Colistin (polymyxin E)
- Tigecycline
- Minocycline
- Cefiderocol
- High-dose sulbactam
Combination therapy may be considered for XDR strains
Avoid unnecessary antibiotics to reduce pressure

Prevention

Hand hygiene and contact precautions in hospitals
Environmental cleaning and disinfection
Surveillance of ICU and high-risk wards
Isolation or cohorting of infected patients
Antimicrobial stewardship to prevent resistance emergence
Regular monitoring of device-related infections (e.g., catheters, ventilators)

Fig. Acinetobacter growth on CLED agar of urine culture

Keynotes

Acinetobacter baumannii is a critical priority pathogen (WHO list) due to MDR/XDR resistance
Commonly associated with ICU outbreaks
Has high environmental resilience, surviving on dry surfaces for weeks
Accurate identification and susceptibility testing are crucial
Treatment options are limited, and resistance is rising
Prevention and strict infection control measures are vital

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