Table 1.

Drug resistance mechanisms of Acinetobacter baumannii¹

Drug class	Mechanism of resistance	Example of effector molecules	Reference(s)
Aminoglycosides	Modifying enzymes
	Acetyltransferase	ACC	Bakour et al. (2013)
	16S rRNA methylation	ArmA	Doi et al. (2007)
	Phosphotransferase	APHA1, StrA, StrB	McGann et al. (2014), Nigro et al. (2013)
	Adenylytransferase	AadAB	Bakour et al. (2013)
	Efflux pump	AdeABC, AdeM	Magnet et al. (2001), Su et al. (2005)
Carbapenems	Carbapenemases	Oxa-23, -58, -64, -65, -66, -68, -70, -71, -78, -79, -80	Perez et al. (2007)
	Loss of protein function	CarO	Mussi et al. (2005)
	Decreased expression	33–36 kDa OMP	Clark (1996)
	Efflux pump	AdeIJK	Coyne et al. (2011)
Cephalosporins	Efflux pump	AdeIJK	Coyne et al. (2011)
	β-lactamases	AmpC	Rezaee et al. (2013)
Lincosamides	Efflux pump	AdeFGH, AdeIJK, MsrA, MsrB	Coyne et al. (2011), Taitt et al. (2014)
Macrolides	Efflux pump	AdeABC, MsrA, MsrB	Magnet et al. (2001), Taitt et al. (2014)
Monobactams	Efflux pump	AdeIJK	Coyne et al. (2011)
Penicillins	Altered penicillin-binding proteins	PBP1-3,5-8	Cayo et al. (2011)
	β-lactamases	PER-1, TEM-1, VEB-1, CTX-M	Bae et al. (2011), Perez et al. (2007), Walther-Rasmussen & Hoiby (2004)
	Metallo-β-lactamases	IMP-1, -2, -4, -5, -6, -11 VIM-2, NDM-1	Walsh et al. (2005)
	Efflux pump	AdeABC, AdeIJK	Yum et al. (2002), Jones et al. (2014)
	Decreased expression	46 kDa OMP	Magnet et al. (2001), Coyne et al. (2011)
Polypeptides	Gene mutations	pmrAB	Lesho et al. (2013)
	phosphoethanolamine modification of lipid A	PmrC	Arroyo et al. (2011)
Quinolones/Fluoroquinolone	Efflux pump	AdeABC, AdeIJK, AdeM, AdeFGH	Magnet et al. (2001), Su et al. (2005), Coyne et al. (2011)
	Production of protective proteins	QnrA	Touati et al. (2008)
	Gene mutations	gyrA, parC	Hamouda & Amyes,
Rifamycin	Efflux pump	AdeIJK	Coyne et al. (2011)
	ADP-ribosyltransferase	ARR-2	Houang et al. (2003)
Sulfonamides	Drug-resistant variant	Sul1, Sul2	Nigro et al. (2013)
Tetracyclines	Efflux pump	AdeABC, AdeIJK	Magnet et al. (2001),
		TetAB	Coyne et al. (2011)
	Decreased expression	CarO, OmpA38, OmpA32, OmpW	Guardabassi et al. (2000)
Other	Aminocoumarin
	Efflux pump	AdeIJK	Coyne et al. (2011)
	Chloramphenicol
	Efflux pump	AdeABC, AdeFGH, AdeIJK, CmlA, CraA	Magnet et al. (2001), Coyne et al. (2011)
	Acetyltransferase	Cat	Turton et al. (2005)
	Fusidic acid
	Efflux acid	AdeIJK	Coyne et al. (2011)
	Streptogramin
	Efflux pump	MsrA, MsrB	Taitt et al. (2014)
	Tigecycline
	Efflux pump	AdeABC, AdeIJK	Coyne et al. (2011)
	Trimethoprim
	Efflux pump	AdeABC, AdeFGH, AdeIJK, AdeM	Coyne et al. (2011)
	Drug-resistant variant	FolA, DrfA1, DrfA7, DrfA19	Taitt et al. (2014)

¹Drug-resistance mechanisms vary greatly among strains and combinations of drug resistance genes are different. Many of these genes have been acquired by A. baumannii to confer drug-resistance, while some occur naturally.