What are Multi-Drug Resistant Organisms (MDRo) bacteria?

Multi-Drug Resistant Organisms (MDROs): Definition and Classification

Multi-Drug Resistant Organisms (MDROs) are bacteria that have acquired non-susceptibility to at least one agent in three or more antimicrobial categories, posing significant threats to public health due to limited treatment options and increased morbidity and mortality. 1

Key MDROs and Their Definitions

Standard Classification System

• MDR (Multi-Drug Resistant): Acquired non-susceptibility to at least one agent in three or more antimicrobial categories 1
• XDR (Extensively Drug-Resistant): Non-susceptibility to at least one agent in all but two or fewer antimicrobial categories (bacteria remain susceptible to only one or two categories) 1
• PDR (Pandrug-Resistant): Non-susceptibility to all agents in all antimicrobial categories 1

Common MDROs in Healthcare Settings

Gram-Positive MDROs:

• Methicillin-Resistant Staphylococcus aureus (MRSA) 2
• Vancomycin-Resistant Enterococci (VRE) 2

Gram-Negative MDROs:

• Carbapenem-Resistant Enterobacterales (CRE) 2
• Carbapenem-Resistant Pseudomonas aeruginosa (CRPA) 2
• Carbapenem-Resistant Acinetobacter baumannii (CRAB) 2
• Extended-Spectrum β-Lactamase (ESBL)-producing Enterobacterales 2

Epidemiology and Impact

• MDROs are a leading cause of healthcare-associated infections worldwide 2
• According to European Antimicrobial Resistance Surveillance Network (EARS-Net), alarming increases in carbapenem resistance have been reported in K. pneumoniae (7.9%), P. aeruginosa (16.5%), and A. baumannii (>30%) 2
• MDRO infections lead to increased mortality, longer hospital stays, and higher healthcare costs 2, 3
• Patients with MDRO infections have 2.89 times higher odds of ICU mortality compared to non-MDRO infections 3

Clinical Significance

• MDRO infections represent a clinical challenge due to limited treatment options, often requiring last-resort antibiotics with higher toxicity or reduced efficacy 2
• Appropriate antibiotic therapy significantly improves survival (92.9% vs 82.2% for inappropriate therapy) 3
• Infections with MDROs require longer ICU stays and greater resource utilization 3

Testing and Identification

• To ensure correct application of MDRO definitions, bacterial isolates should be tested against all or nearly all antimicrobial agents within the relevant categories 1
• Selective reporting and suppression of susceptibility results should be avoided 1
• Effective sensitivity testing is essential to identify MDROs and direct appropriate antibiotic choices 4

Management Considerations

• Infectious disease specialist consultation is recommended for managing MDRO infections due to:

  • Limited number of active antimicrobial agents 2
  • Need for optimization of pharmacokinetics/pharmacodynamics 2
  • Requirement for complete evaluation of disease extent and host immunity 2

• For specific MDROs like NDM-producing Pseudomonas:

  • Ceftazidime/avibactam plus aztreonam is recommended as first-line therapy 5
  • Cefiderocol may be considered as an alternative option 5

Prevention and Control

• Meticulous infection prevention and control measures are essential to limit MDRO propagation 4
• Effective antimicrobial stewardship programs help decrease antibiotic pressure that drives selection of MDROs 4
• Aggressive infection control measures are crucial to prevent spread of highly resistant organisms like NDM-producers 5

Common Pitfalls and Caveats

• Misclassification of resistance patterns can lead to inappropriate antibiotic selection 1
• Incomplete antimicrobial susceptibility testing may result in failure to identify true MDROs 1
• Overuse of broad-spectrum antibiotics between initial intervention and reoperation is a significant risk factor for emergence of MDROs 2
• Use of antibiotics for more than 5 days before diagnosis of complications (e.g., anastomotic leakage) increases risk of MDRO acquisition 2