Table 1.

Mechanism of drug resistance in Acinetobacter baumannii.

Resistant mechanism	Class or subgroup	Gene	References
β-Lactamases	Ambler class A	TEM, SHV, PER, VEB, KPC	Černiauskienė et al. (2023)
	Ambler class B	IMP, VIM, SIM, NDM	Chen et al. (2017), López et al. (2019), Ayibieke et al. (2018)
	Ambler class C	AmpC	Liu and Liu (2015)
	Ambler class D	OXA23 family OXA24 family OXA51 family OXA58 family OXA143 family OXA235 family	Lin and Lan (2014), June et al. (2016), Huang et al. (2015), Donald et al. (2000), Avci et al. (2023), Zhao et al. (2019), Oliveira et al. (2019), Liao et al. (2015)
Aminoglycoside modifying enzymes	Aminoglycoside acetyltransferases (AACs)	AAC(3)-I AAC(3)-II AAC(6′)-I ANT(2″)-I ANT(2″)-II APH(3′)-I APH(3″)-II	Lin and Lan (2014), Lin et al. (2015), Sheikhalizadeh et al. (2017)
	Aminoglycoside nucleotidyltranferases (ANTs)
	Aminoglycoside phosphotransferases (APHs)
	16S rRNA methylase	armA	Gholami et al. (2017)
Changing the target locations	DNA gyrase and topoisomerase	gyrA, parC	Gu et al. (2015)
	Penicillin-binding protein (PBPs)	PBP2, PBP1	Cochrane and Lohans (2020), Toth et al. (2022)
Formation of biofilms	Biofilms	BfmRS, abaI, epsA, pglC, ompA	Geisinger et al. (2018), Yang et al. (2019), Romero et al. (2008)
Overexpression of the external discharge pumping system	RND superfamily	AdeABC AdeIJK AdeDE AdeFGH	Yoon et al. (2013), Modarresi et al. (2015), Chang et al. (2016), Lin et al. (2014), Meyer et al. (2022), Darby et al. (2023), AlQumaizi et al. (2022), Hou et al. (2012)
	MFS superfamily	TetA, TetB	Lomovskaya et al. (2018), Sumyk et al. (2021)
		CraA	Foong et al. (2019)
		AmvA	Rostami et al. (2021)
	MATE family	AbeM	Srinivasan et al. (2015)
	SMR family	AbeS	Lytvynenko et al. (2016)
	ABC superfamily	MsbA	Hammerstrom et al. (2015)
Changes in outer membrane pore proteins	Omp	CarO, HMP, OprD	Wu et al. (2016), Smani et al. (2014), Fonseca et al. (2013)
Mechanisms of resistance to tigecycline
Efflux pump	RND superfamily	AdeABC AdeIJK AdeFGH	Jo and Ko (2021), Salehi et al. (2021), Hornsey et al. (2010), Lin et al. (2014), Gerson et al. (2018), Deng et al. (2014), Li et al. (2017)
	ABC superfamily	MsbA	Chen et al. (2014)
		MacAB-TolC	Lin et al. (2017b)
	MFS superfamily	tetA, tet(Y)	Wang et al. (2021) Liu et al. (2023)
	AcrAB-TolC	hns
Modified enzyme mediated	Tet(X)	Tet(X), Tet(X3), Tet(X5), Tet (X6)	Cui et al. (2021), He et al. (2019), Chen et al. (2021)
Change in outer membrane permeability		plsC abrP gnaA	Li et al. (2015), Li et al. (2016), Xu et al. (2019)
Changes in drug targets		rpsJ trm rrf	Hammerstrom et al. (2015), Beabout et al. (2015), Chen et al. (2014), Ghalavand et al. (2022), Zheng et al. (2023), Hua et al. (2021)
DNA damage-induced reactions		recA, recBCD	Ajiboye et al. (2018)
Mechanisms of resistance to colistin
Modification of LPS structures	PEtN	PmrA, PmeB, PmrC EptA	Olaitan et al. (2014), Potron et al. (2019), Sun et al. (2020), Kabic et al. (2023), Nurtop et al. (2019), Gerson et al. (2020) Trebosc et al. (2019), Ye et al. (2023)
		mcr-4.3, mcr-1, mcr-2, mcr-3	Martins-Sorenson et al. (2020), Snyman et al. (2021), Ma et al. (2019), Al-Kadmy et al. (2020)
	Galactosamine	NaxD	Chin et al. (2015)
Loss of LPS		lpxA, lpxC, lpxD	Moffatt et al. (2011), Nurtop et al. (2019), Jovcic et al. (2021), Thi Khanh Nhu et al. (2016), Carretero-Ledesma et al. (2018), Wand et al. (2015)
Overexpression of efflux pumps	EmrAB effector pump system	emrB	Lin et al. (2017a), Ni et al. (2016)
Mutations in outer membrane constituent proteins	Non-LPX proteins lipoprotein	lpsB LptD VacJ, PldA	Hood et al. (2013), Dafopoulou et al. (2015), Lean et al. (2014), Yang W. et al. (2023); Yang Y. et al. (2023) Bojkovic et al. (2015) Thi Khanh Nhu et al. (2016)