Table 1.

Comparison of amino acid substitutions, inhibitory properties, and epidemiology of IRS β-lactamases

β-Lactamase	Amino acid at position no.:a														IC50 (μM) (CLA/TAZ)b	Strainc	Country (yr)d	Reference(s)
	8	35	54	69	130	140	146	187	192	193	234	235	238	240
SHV-1	I	L	G	M	S	A	A	A	K	L	K	T	G	E	0.17/0.11	K. pneumoniae	Switzerland (1972)	36
SHV-10			Del		G	R			N	V			S	K	6.9/1.3	E. coli	Greece (1997)	37
SHV-26								T							0.48/NDe	K. pneumoniae	Taiwan (2001)	8
SHV-49				I											1.5/2.5	K. pneumoniae	France (2004)	13
SHV-56		Q									R				2.5/0.75	K. pneumoniae	France (2008)	14
SHV-72	F						V				R				1.72/0.08	K. pneumoniae	Portugal (2008)	31
SHV-84											R				2.21/0.03	E. coli	Portugal (2010)	26
SHV-107		Q										A			1.53/0.11	K. pneumoniae	Portugal (2009)	28; this study

^aNumbering according to Ambler et al. (1).

^bValues of clavulanate (CLA) and tazobactam (TAZ) for the different IRS β-lactamases. SHV-1, SHV-72, and SHV-84, SHV-10, and SHV-107 values were determined using 200 μM ticarcillin, 50 mM nitrocefin, and 200 μM penicillin, respectively, which were incubated with the inhibitor for 5 min at 37°C at pH 7; SHV-49 and SHV-56 values were determined by benzylpenicillin (100 μM) hydrolysis after 3 min of preincubation at 30°C; and SHV-26 values were determined after 10 min of preincubation of nitrocefin with the clavulanate at room temperature. IC₅₀, 50% inhibitory concentration.

^cStrain producing IRS β-lactamase, in the first report.

^dCountry that first reported the β-lactamase, and year (in parentheses).

^eND, not determined.