TABLE 3.

Examples of resistance to antimicrobials by enzymatic inactivation^a

Resistance mechanism	Resistance gene(s)	Gene product	Resistance phenotype	Bacteria involved	Location of the resistance geneb
Hydrolytic degradation	bla	β-lactamases	β-lactam antibiotics	Various Gram+, Gram–, aerobic, anaerobic bacteria	P, T, GC, C
	ere(A), ere(B)	esterases	macrolides	Gram+, Gram– bacteria	P, GC
	vgb(A), vgb(B)	lactone hydrolases	streptogramin B antibiotics	Staphylococcus, Enterococcus	P
Chemical modification	aac, aad (ant), aph	acetyl-, adenyl-, phosphotransferases	aminoglycosides	Gram+, Gram–, aerobic bacteria	T, GC, P, C
	aad (ant)	adenyltransferases	aminoglycosides/aminocyclitols	Gram+, Gram–, aerobic bacteria	T, GC, P, C
	catA, catB	acetyltransferases	chloramphenicol	Gram+, Gram–, aerobic, anaerobic bacteria	P, T, GC, C
	vat(A-G)	acetyltransferases	streptogramin A antibiotics	Bacteroides, Staphylococcus, Enterococcus, Lactobacillus, Yersinia	P, C
	mph(A-G)	phosphotransferases	macrolides	Gram+, Gram– bacteria	P, T, C
	lnu(A-P)	nucleotidyltransferases	lincosamides	Gram+, Gram– bacteria	P
	tet(X), tet(37), tet(56)	oxidoreductases	tetracyclines	Gram– bacteria, unknown, Legionella	T, P

^a Modified from reference 8.

^b Abbreviations: P, plasmid; T, transposon; GC, gene cassette; C, chromosomal DNA.