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

Introduction

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

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

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

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)

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

Further Readings

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC3442836/
2. https://www.cdc.gov/acinetobacter/about/index.html
3. https://gardp.org/stories/meet-acinetobacter-baumannii/
4. https://academic.oup.com/femspd/article/71/3/292/475786
5. https://www.webmd.com/a-to-z-guides/what-to-know-about-acinetobacter-baumannii
6. https://www.msdmanuals.com/professional/infectious-diseases/gram-negative-cocci-and-coccobacilli/acinetobacter-infections
7. https://www.nature.com/articles/nrmicro1789
8. https://journals.asm.org/doi/10.1128/cmr.00058-07
9. https://web.sanfordguide.com/e1f1b28667ed4739a3c5cd85dc24f64f