Integrons common in poultry litter. (A) Typical Tn21-like Class 1 Integron (28). Nonmobile resistance genes lacking attC are sul1, sulfonamide resistance; and qacEΔ1, quaternary ammonium compound resistance. Example mobile resistance genes include aadA, aminoglycoside adenyltransferase; and oxa, β-lactamase. Other genes are attI1, specific insertion site; intI1, integrase; tni, integron transposition operon; and arrows, inverted repeats involved in transposition (B) Class 2 Integron, Tn7 (30, 40). Mobile resistance genes are dfr1, trimethoprim; sat, streptothricin; aadA, aminoglycoside adenyltransferase. Other genes are attI2, specific insertion site; intI2, integrase; tns, Tn7 transposition operon; arrows, inverted repeats involved in transposition (not to scale).