Multidrug-resistant organism

Background

Microorganisms, predominantly bacteria, that are resistant to one or more classes of antimicrobial agents
Definition varies from hospital to hospital or country to country

European CDC Definitions

Defined by the European CDC^[1] as non-susceptibility to at least one agent in three or more categories of antimicrobials, with the categories varying by organism
Multidrug resistant (MDR) is non-susceptible to at least 1 agent in at least 3 categories
- For Staphylococcus aureus, it automatically includes MRSA, but requires resistance in >3 categories
Extensively drug-resistant (XDR) is non-susceptible to at least 1 agent in all but 2 categories
Pan-drug resistant (PDR) is non-susceptible to all listed agents
For species with intrinsic resistance to a category or agent, it should be excluded before counting

Category	Agent	Species With Intrinsic Resistance
Staphylococcus aureus
Aminoglycocides	gentamicin
Ansamycins	rifampin
Anti-MRSA cephalosporins	ceftaroline
Anti-staphylococcal β-lactams	oxacillin or cefoxitin
Fluoroquinolones	ciprofloxacin or moxifloxacin
Folate antagonists	TMP-SMX
Fucidanes	fusidic acid
Glycopeptides	vancomycin, teicoplanin, telavancin
Glycylcyclines	tigecycline
Lincosamides	clindamycin
Lipopeptides	daptomycin
Macrolides	erythromycin
Oxazolidinones	linezolid
Phenicols	chloramphenicol
Phosphonic acids	fosfomycin
Streptogramins	quinupristin-dalfopristin
Tetracyclines	tetracycline, doxycycline, minocycline
Enterococcus
Aminoglycosides, except streptomycin	gentamicin (high level)
Streptomycin	streptomycin (high level)
Carbapenems	imipenem, meropenem, doripenem	Enterococcus faecium
Fluoroquinolones	ciprofloxacin, levofloxacin, moxifloxacin
Glycopepties	vancomycin, teicoplanin
Glycyclcyclines	tigecycline
Lipopeptides	daptomycin
Oxazolidinones	linezolid
Penicillins	ampicillin
Streptogramins	quinupristin-dalfopristin	Enterococcus faecalis
Tetracyclines	doxycycline, minocycline
Enterobacterales
Aminoglycosides	gentamicin, tobramycin, netilmicin	Providencia rettgeri, Providencia stuartii
Aminoglycosides	tobramycin	Providencia rettgeri, Providencia stuartii
Anti-MRSA cephalosporins	ceftaroline	only approved for Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca
Antipseudomonal penicillins with β-lactamase inhibitors	ticarcillin-clavulanic acid, piperacillin-tazobactam	Escherichia hermannii
Carbapenems	ertapenem, imipenem, meropenem, doripenem
1st & 2nd generation cephalosporins	cefazolin	Citrobacter freundii, Klebsiella aerogenes, Enterobacter cloacae, Hafnia alvei, Morganella morganii, Proteus penneri, Proteus vulgaris, Providencia rettgeri, Providencia stuartii, Serratia marcescens
1st & 2nd generation cephalosporins	cefuroxime	Morganella morganii, Providencia penneri, Providencia vulgaris, Serratia marcescens
3rd & 4th generation cephalosporins	cefotaxime or ceftriaxone, ceftazidime, cefepime
Cephamycins	cefoxitin, cefotetan	Citrobacter freundii, Klebsiella aerogenes, Enterobacter cloacae, Hafnia alvei
Fluoroquinolones	ciprofloxacin
Folate antagonists	TMP-SMX
Glycylcyclines	tigecycline	Morganella morganii, Proteus mirabilis, Providencia penneri, Providencia vulgaris, Providencia rettgeri, Providencia stuartii
Monobactams	aztreonam
Penicillins	ampicillin	Citrobacter koseri, Citrobacter freundii, Klebsiella aerogenes, Enterobacter cloacae, Enterobacter hermanii, Hafnia alvei, Klebsiellae spp., Morganella morganii, Providencia penneri, Providencia vulgaris, Providencia rettgeri, Providencia stuartii, Serratia marcescens
Penicillins plus β-lactamase inhibitors	amoxicillin-clavulanic acid	Citrobacter freundii, Klebsiella aerogenes, Enterobacter cloacae, Hafnia alvei, Morganella morganii, Providencia rettgeri, Providencia stuartii, Serratia marcescens
Penicillins plus β-lactamase inhibitors	ampicillin-sulbactam	Citrobacter freundii, Citrobacter koseri, Klebsiella aerogenes, Enterobacter cloacae, Hafnia alvei, Providencia rettgeri, Serratia marcescens
Phenicols	chloramphenicol
Phosphonic acid	fosfomycin
Polymyxins	colistin	Morganella morganii, Proteus mirabilis, Providencia penneri, Providencia rettgeri, Providencia stuartii, Serratia marcescens
Tetracyclines	tetracycline	Morganella morganii, Proteus mirabilis, Providencia penneri, Providencia vulgaris, Providencia rettgeri, Providencia stuartii,
Tetracyclines	doxycycline, minocycline	Morganella morganii, Providencia penneri, Providencia vulgaris, Providencia rettgeri, Providencia stuartii
Pseudomonas aeruginosa
Aminoglycosides	gentamicin, tobramycin, amikacin, netilmicin
Antipseudomonal carbapenems	imipenem, meropenem, doripenem
Antipseudomonal cephalosporins	ceftazidime, cefepime
Antipseudomonal fluoroquinolones	ciprofloxacin, levofloxacin
Antipseudomonal penicillins plus β-lactamase inhibitors	ticarcillin-clavulanic acid, piperacillin-tazobactam
Monobactams	aztreonam
Phosphonic acids	fosfomycin
Polymyxins	colistin, polymyxin B
Acinetobacter
Aminoglycosides	gentamicin, tobramycin, amikacin, netilmicin
Antipseudomonal carbapenems	imipenem, meropenem, doripenem
Antipseudomonal fluoroquinolones	ciprofloxacin, levofloxacin
Antipseudomonal penicillins plus β-lactamase inhibitors	ticarcillin-clavulanic acid, piperacillin-tazobactam
Extended-spectrum cephalosporins	ceftriaxone, ceftazidime, cefepime
Folate antagonists	TMP-SMX
Phosphonic acids	fosfomycin
Penicillins plus β-lactamase inhibitors	ampicillin-sulbactam
Polymyxins	colistin, polymyxin B
Tetracyclines	tetracycline, doxycycline, minocycline

↑ Magiorakos AP, Srinivasan A, Carey RB, Carmeli Y, Falagas ME, Giske CG, Harbarth S, Hindler JF, Kahlmeter G, Olsson-Liljequist B, Paterson DL, Rice LB, Stelling J, Struelens MJ, Vatopoulos A, Weber JT, Monnet DL. Multidrug-resistant, extensively drug-resistant and pandrug-resistant bacteria: an international expert proposal for interim standard definitions for acquired resistance. Clin Microbiol Infect. 2012 Mar;18(3):268-81. doi: 10.1111/j.1469-0691.2011.03570.x. Epub 2011 Jul 27. PMID: 21793988.

[1] Magiorakos AP, Srinivasan A, Carey RB, Carmeli Y, Falagas ME, Giske CG, Harbarth S, Hindler JF, Kahlmeter G, Olsson-Liljequist B, Paterson DL, Rice LB, Stelling J, Struelens MJ, Vatopoulos A, Weber JT, Monnet DL. Multidrug-resistant, extensively drug-resistant and pandrug-resistant bacteria: an international expert proposal for interim standard definitions for acquired resistance. Clin Microbiol Infect. 2012 Mar;18(3):268-81. doi: 10.1111/j.1469-0691.2011.03570.x. Epub 2011 Jul 27. PMID: 21793988.

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