Comparison of Clinical & Laboratory Standards Institute standards in Antimicrobial Susceptibility Among the Carbapenemase Producing Enterobacteriaceae

Figures & data

Table 1.  Performance standards for antimicrobial susceptibility testing.

Agent	Previous breakpoints M100-S19^† MIC (μg/ml)			Current breakpoints M100–27^‡ MIC (μg/ml)
	S	I	R	S	I	R
Doripenem	–	–	–	≤1	2	≤4
Ertapenem	≤2	4	≥8	≤0.5	1	≥2
Imipenem	≤4	8	≥16	≤1	2	≥4
Meropenem	≤4	8	≥16	≤1	2	≥4

† 2009 CLSI criteria [9].

‡ 2017 CLSI criteria [5].

I: Intermediate; MIC: Minimum inhibitory concentration; R: Resistant; S: Susceptible.

Table 2.  Individual carbapenem susceptibility among all Carbapenem-resistant Enterobacteriaceae isolates analyzed.

Individual carbapenems	Previous breakpoints M100-S19^†				Current breakpoints M100–27^‡
	Susceptible		Nonsusceptible		Susceptible		Nonsusceptible
	n	%	n	%	n	%	n	%
Ertapenem^§	6	11.3	47	88.7	5	9.4	48	90.6
Imipenem	8	14.8	46	85.2	5	9.3	49	90.7
Doripenem^¶	nd	nd	nd	nd	5	9.6	47	90.4
Meropenem	7	13.0	47	87.0	5	9.3	49	90.7

† 2009 CLSI criteria [9].

‡ 2017 CLSI criteria [5].

§ Ertapenem use was not indicated for one isolate.

¶ Doripenem use was not indicated for two isolates.

CRE: Carbapenem resistant Enterobacteriaceae; nd: Doripenem interpretation was not defined in the previous breakpoints.

Table 3.  Individual carbapenem susceptibility among blaKPC gene negative isolates.

Individual carbapenems	Previous breakpoints M100-S19^†		Current breakpoints M100–27^‡
	Susceptible	Nonsusceptible	Susceptible	Nonsusceptible
Ertapenem	6	2	5	3
Imipenem	7	2	5	4
Doripenem	ND	ND	4	3
Meropenem	7	2	5	4

† 2009 CLSI criteria [9].

‡ 2017 CLSI criteria [5].

ND: Doripenem interpretation was not defined in the previous breakpoint.

Table 4.  Susceptibility changes (susceptible to nonsusceptible) between the previous Clinical and Laboratory Standards Institute criteria and the current criteria among blaKPC genes (negative and positive).

Individual carbapenems^†	blaKPC gene negative	blaKPC gene positive	Total number of changes
Ertapenem	1	0	1
Imipenem	2	1	3
Meropenem	2	0	2

† Doripenem susceptibilities were not compared.

Table 5.  Carbapenem resistance phenotypes implicated in all isolates (n = 54).

Carbapenem resistance phenotype^†	GN69 AST card (n; percentage)	XN06 AST card (n; percentage)
Extended spectrum beta-lactamase	47 (87.0%)	47 (87.0%)
Impermeability (carbapenems and cephamycins)	46 (85.2%)	48 (88.8%)
Carbapenemase (metallo- or KPC)	45 (83.3%)	49 (90.7%)
Penicillinase (acquired or wild-type)	2 (3.7%)	1 (1.9%)
High level AmpC (HL-CASE)	2 (3.7%)	1 (1.9%)
Inhibitor-resistant PASE (IRT or OXA)	0 (0%)	1(1.9%)

† Most isolates exhibited more than one phenotype

AST: antimicrobial susceptibility testing; HL-CASE: High-level AmpC B-lactamase; IRT: Inhibitor-resistant TEM B-lactamases; KPC: Klebsiella pneumoniae carbapenemase; OXA: Oxacillinase group of B-lactamases.

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Clinical and Laboratory Standards Institute. In: Performance Standards for Antimicrobial Susceptibility Testing. 27^th M100. Clinical and Laboratory Standards Institute, PA, USA (2017).

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