TABLE 3.

Aminoglycoside MICs stratified by presence or absence of AMEs^a

AME pattern	No. of strains	Gentamicin			Tobramycin			Amikacin			Plazomicin
		Median MIC (μg/ml)		P valueb	Median MIC (μg/ml)		P valueb	Median MIC (μg/ml)		P valueb	Median MIC (μg/ml)		P valueb
		Pattern present	Pattern absent		Pattern present	Pattern absent		Pattern present	Pattern absent		Pattern present	Pattern absent
No AMEs	1	0.25	NAc	NA	0.25	NA	NA	1	NA	NA	0.25	NA	NA
AAC(6′)-Ib only	17	0.5	16	0.01	16	45.2	0.0008	16	16	NSd (0.31)	0.25	0.5	0.046
AAC(3)-IV, AAC(6′)-Ib	4	22.6	1	NS (0.09)	128	16	0.02	11.3	16	NS (0.37)	0.70	0.5	NS (0.45)
APH(3′)-Ia, AAC(6′)-Ib	12	0.71	1	NS (0.24)	16	16	NS (0.20)	16	16	NS (0.74)	0.35	0.5	NS (0.50)
AAC(3)-IV, APH(3′)-Ia, AAC(6′)-Ib	15	32	1	0.01	128	16	0.001	16	16	NS (0.83)	0.5	0.25	0.03
ANT(2″)-Ia, APH(3′)-Ia, AAC(6′)-Ib	1	32	NA	NA	64	NA	NA	16	NA	NA	0.5	NA	NA
Any AAC(3)-IV	19	32	0.5	0.0006	128	16	<0.0001	16	16	NS (0.58)	0.5	0.25	0.01
Any APH(3′)-Ia	28	16	1	0.03	16	16	0.048	16	16	NS (0.82)	0.5	0.25	NS (0.13)

^aThe four AMEs tested were AAC(6′)-Ia, APH(3′)-IV, AAC(3)-Ia, and ANT(2″)-Ia. AAC(6′)-Ia was present in all strains except one. On the AAC(6′)-Ib backbone, the addition of other AMEs resulted in significantly higher MICs of gentamicin, tobramycin, and plazomicin. The key AME was AAC(3)-IV, which if present, was associated with significantly higher MICs of gentamicin, tobramycin, and plazomicin. The presence of APH(3′)-Ia was not significantly associated with elevated MICs of any aminoglycosides tested. The single strain with ANT(2″)-Ia, AAC(6′)-Ib, and APH(3′)-IV exhibited higher gentamicin, tobramycin, and plazomicin MICs than strains with only AAC(6′)-Ib and APH(3′)-IV.

^bP values denote the statistically significant difference in log₂ MICs of the aminoglycosides among the groups with and without specific AMEs.

^cNA, not applicable.

^dNS, not significant.