Multidrug-resistant organisms (MDRO)

MDRO pathogens that are frequently implicated in severe healthcare-associated infections (HAIs) and have important infection control implications are the following:

• Gram-positive: methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE);
• Gram-negative: Pseudomonas aeruginosa, Acinetobacter baumanni and Enterobacteriaceae that are resistant to at least one agent in three or more antimicrobial categories (see table) and organisms such as Stenotrophomonas maltophilia and Burkholderia cepacia, that are intrinsically resistant to the broadest-spectrum antimicrobial agents.

Table: Antimicrobial categories used to define MDR gram-negative bacteria.

Enterobacteriaceae	Pseudomonas aeruginosa	Acinetobacter spp
Aminoglycosides	Aminoglycosides	Aminoglycosides
Cephalosporins	Antipseudomonal cephalosporins (ceftazidime, cefepime)	Antipseudomonal carbapenems (Imipenem, Meropenem, Doripenem)
Carbapenems (Ertapenem, Imipenem, Meropenem, Doripenem)	Antipseudomonal carbapenems (Imipenem, Meropenem, Doripenem)	Antipseudomonal fluoroquinolones (ciprofloxacin, levofloxacin)
Antipseudomonal penicillins + beta-lactamase inhibitors	Antipseudomonal fluoroquinolones (ciprofloxacin, levofloxacin)	Antipseudomonal penicillins + beta-lactamase inhibitors
Fluoroquinolones	Antipseudomonal penicillins + beta-lactamase inhibitors (piperacillin/tazobactam, ticarcillin-clavulanic acid)	Extended spectrum cephalosporins (cefotaxime, ceftriaxone, ceftazidime, cefepime)
Folate pathway inhibitors	Monobactams	Folate pathway inhibitors
Glycylcyclines	Phosphonic acids	Penicillins + beta-lactamase inhibitors (ampicillin/sulbactam)
Monobactams	Polymyxins	Polymyxins
Penicillins		Tetracyclines
Phenicols
Phosphonic acids
Polymyxins
Tetracyclines

References

• Magiorakos AP, Srinivasan A, Carey RB, Carmeli Y, Falagas ME, Giske CG, et al. Multidrug-resistant, extensively drug-resistant and pandrug-resistant bacteria: An international expert proposal for interim standard definitions for acquired resistance. Clin Microbiol Infect. 2012; 18:268-81.