TABLE 1.

Rate of hydrolysis of ertapenem and meropenem for 78 strains of Gram-negative bacilli by MIC of carbapenem, results of modified Hodge test, and the molecular mechanism of carbapenemase-producing isolates

Enzyme	Species (no. of strains)	No. of isolates with positive modified Hodge test result	MIC (range) (mg/liter)			UPLC hydrolysis rate [% (range)]
			Imipenem	Ertapenem	Meropenem	Ertapenem	Meropenem
Carbapenemase-producing strains (n = 41)
KPC	Klebsiella pneumoniae (2)	2	1 to >32	4 to >32	2 to >32	100	100
IMP	Escherichia coli (1)	1	1	0.5	0.5	100	100
	Pseudomonas aeruginosa (1)	1	>32	>32	>32	100	100
VIM	Pseudomonas aeruginosa (2)	0	>32	>32	>32	44 to 100	98 to 100
	Klebsiella pneumoniae (1)	1	8	3	1	25	51
NDM-1	Citrobacter freundii (1)	1	8	>32	12	100	100
	Acinetobacter baumannii (1)	0	>32	>32	>32	63	78
	Klebsiella pneumoniae (2)	1	16 to >32	>32	6 to >32	97 to 100	100
	Escherichia coli (1)	0	1.5	1.5	0	89	91
OXA-48	Klebsiella pneumoniae (6)	6	0.75 to >32	1 to >32	0.75 to 16	98 to 100	99 to 100
	Escherichia coli (5)	5	1.5 to >32	1.5 to >32	0.75 to >32	99 to 100	99 to 100
	Citrobacter freundii (2)	2	1 to 3	1.5 to 4	0.38 to 2	96 to 100	100
	Serratia marcescens (2)	2	1.5 to 16	1.5 to 16	0.75 to 8	100	100
OXA-23	Acinetobacter baumannii (10)	8	24 to >32	32 to >32	32 to >32	38 to >100	46 to >100
OXA-40	Acinetobacter baumannii (2)	1	>32	>32	>32	69 to 93	70 to 93
OXA-51a	Acinetobacter baumannii (1)	1	>32	>32	>32	69	69
OXA-58	Acinetobacter baumannii (1)	0	2	12	1.5	93	92
MDRb non-carbapenemase-producing strains (n = 22)	Citrobacter freundii (1)	0	0.125	0.008	0.032	0	0
	Enterobacter cloacae (4)	0	0.38 to 32	0.19 to >32	0.19 to 12	0 to 11	0 to 8
	Escherichia coli (11)	0	0.125 to 1	0.008 to 16	0.012 to 4	0 to 15	0 to 4
	Klebsiella pneumoniae (5)	0	0.125 to 0.5	0.094 to 3	0.016 to 0.38	0 to 17	0 to 4
	Klebsiella oxytoca (1)	0	0.125	0.016	0.023	0	0
Susceptible strains (n = 15)	Escherichia coli (5)	0	0.016 to 0.25	0.008 to 0.032	0.008 to 0.19	0 to 2	0 to 9
	Citrobacter freundii (2)	0	0.38	0.016 to 0.19	0.032 to 0.064	0	0 to 6
	Klebsiella pneumoniae (2)	0	0.125 to 0.19	0.008 to 0.016	0.032	0	2 to 10
	Klebsiella oxytoca (1)	0	0.19	0.008	0.032	0	0
	Pseudomonas aeruginosa (2)	0	0.15 to 2	0.23 to 12	0.047 to 0.5	0 to 1	0 to 8
	E. cloacae (2)	0	0.19 to 0.25	0.032 to 0.5	0.023 to 0.38	0 to 5	0 to 5
	Acinetobacter baumannii (1)c	0	0.38	3	1.5	0	0

^aAcinetobacter baumannii carrying overproduced OXA-51.

^bMDR, multidrug resistant.

^cAcinetobacter baumannii ATCC 19606 carrying the natural oxacillinase OXA-51.