Table 1.

Definitions of Antimicrobial Resistance

Classification	Pathogen Type	Definition of Resistance
Gram-negative pathogens	ENT (Citrobacter freundii, Escherichia coli, Enterobacter cloacae, Klebsiella pneumoniae, Klebsiella oxytoca, Klebsiella aerogenes, Morganella morganii, Proteus mirabilis, Providencia stuartii, Serratia marcescens), ACB, PsA, and Stenotrophomonas maltophilia	ESBL-producing phenotype: E coli, K pneumoniae, K oxytoca, and P mirabilis isolates confirmed as ESBL positive per commercial panels or based on a result of I or R to antimicrobial susceptibility tests with ESC (ceftriaxone, cefotaxime, ceftazidime, or cefepime) Pip-Tazo: I or R to Pip-Tazo Carbapenem NS: I or R to ETP, IMI (excluded for P mirabilis and M morganii), MER, or DOR PsA and ACB if I or R to IMI, MER, or DOR S maltophilia: all presumed to be NS FQ NS (I or R to ciprofloxacin, levofloxacin, or moxifloxacin [excluded for PsA/ACB]) Multidrug resistance: MDR ENT, ACB, or PsA if I or R to at least 1 drug in 3 of the following 5 classes: ESC (cefotaxime [excluded for PsA/ACB], ceftriaxone [excluded for PsA/ACB], cefepime, or ceftazidime), FQ (ciprofloxacin, levofloxacin, or moxifloxacin [excluded for PsA/ACB]), aminoglycosides, carbapenems (ETP [excluded for PsA/ACB], IMI, MER, or DOR), and piperacillin or Pip-Tazo
Gram-positive pathogens	Enterococcus spp, (VRE), MRSA, and Streptococcus pneumoniae	Enterococcus spp (VRE), Staphylococcus aureus (MRSA) S pneumoniae to: Penicillin resistance: I or R to penicillin Macrolide resistance: I or R to erythromycin, azithromycin, or clarithromycin FQ resistance: I or R to levofloxacin or moxifloxacin Extended-spectrum cephalosporin resistance: I or R to ceftriaxone, cefotaxime, or cefepime Tetracycline resistance: I or R to doxycycline or tetracycline

Abbreviations: ACB, Acinetobacter baumannii species; DOR, doripenem; ESC, extended-spectrum cephalosporins; ENT, Enterobacterales; ESBL, extended-spectrum β-lactamase; ETP, ertapenem; FQ, fluoroquinolone; I, intermediate susceptibility; IMI, imipenem; MDR, multidrug-resistant; MER, meropenem; MRSA, methicillin-resistant Staphylococcus aureus; NS, nonsusceptible; Pip-Tazo, piperacillin-tazobactam; PsA, Pseudomonas aeruginosa; R, resistant susceptibility; VRE, vancomycin-resistant enterococci.