Performance of the VITEK2 System for Detection of Inducible Clindamycin Resistance in Staphylococci

Mi Kyung Kim; Jong Hee Hong; Miae Lee

doi:10.5145/KJCM.2010.13.4.157

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Kim, Hong, and Lee: Performance of the VITEK2 System for Detection of Inducible Clindamycin Resistance in Staphylococci

Original Article

Korean J Clin Microbiol 2010;13(4):157-161.

Published online: 21 December 2010

DOI: https://doi.org/10.5145/KJCM.2010.13.4.157

Performance of the VITEK2 System for Detection of Inducible Clindamycin Resistance in Staphylococci

Mi Kyung Kim, Jong Hee Hong, Miae Lee

Department of Laboratory Medicine, Ewha Womans University School of Medicine, Seoul, Korea

Correspondence: Miae Lee, Department of Laboratory Medicine, Mokdong Hospital, Ewha Womans University School of Medicine, 911-1 Mokdong, Yangcheon-gu, Seoul 158-710, Korea. (Tel) 82-2-2650-5222, (Fax) 82-2-2650-5222, (E-mail) miae@ewha.ac.kr

Received 7 October 2010 Revised 21 October 2010 Accepted 15 November 2010

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background

The Clinical and Laboratory Standards Institute (CLSI) recommends testing for inducible clindamycin resistance in clindamycin non-resistant and erythromycin resistant (CNR-ER) staphylococci by using a D-zone test. Recently, the VITEK2 system was developed to detect inducible clindamycin resistance in staphylococci. We evaluated the performance of the VITEK2 system by comparing it with a D-zone test.

Methods

In detecting inducible clindamycin resistance, a total of 142 clinical isolates of staphylococci were tested by using the VITEK2 Antimicrobial Susceptibility Test (AST)-P601 card (bioMérieux, Marcy l'Etoile, France) and the D-zone test. Of the 142 isolates of staphylococci tested, 114 were CNR-ER staphylococci [40 coagulase-negative staphylococci (CoNS), 74 Staphylococcus aureus] and 28 were staphylococci, either resistant or susceptible to clindamycin and erythromycin (1 CoNS and 27 S. aureus).

Results

Of the 114 CNR-ER staphylococci, 98.6% (73/74) of S. aureus and 32.5% (13/40) of CoNS were inducible clindamycin resistant according to the D-zone test. Overall sensitivity and specificity of the VITEK2 system were 98.8% (85/86) and 98.2% (55/56) respectively, and the agreement between the VITEK2 system and the D-zone test was 98.6% (140/142).

Conclusion

The VITEK2 system shows high concordance with a D-zone test. The inducible clindamycin resistance in staphylococci can be detected easily and conveniently by the VITEK2 system.

Keywords: Inducible clindamycin resistance, Staphylococcus aureus, VITEK2

REFERENCES

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Fig. 1.

Inducible clindamycin resistance positivity by the D-zone test. Arrow, blunting of inhibitory zone of clindamycin; C, clindamycin; E, erythromycin.

Table 1.

Comparison of the D-zone test and the VITEK2 system in detecting of inducible clindamycin resistance in clindamycin susceptible and erythromycin resistant staphylococci isolates (No.=114)

D-zone test	No. of Staphylococcus aureus isolates			No. of coagulase-negative staphylococci isolates
	VITEK2 ICR test			VITEK2 ICR test
	Positive	Negative	Total	Positive	Negative	Total
Positive	72	1	73	13	0	13
Negative	0	1	1	1	26	27
Total	72	2	74	14	26	40

Abbreviation: ICR, inducible clindamycin resistance.

Table 2.

Performance of the VITEK2 system in detecting inducible clindamycin resistance in 142 staphylococci isolates compared to the D-zone test

VITEK2 ICR test	No. of isolates with D-zone test
	S. aureus		CoNS		Total
	Positive	Negative	Positive	Negative	Positive	Negative
Positive	72	0	13	1	85	1
Negative	1	28	0	27	1	55

Abbreviations: CoNS, coagulase-negative staphylococci; ICR, inducible clindamycin resistance

Table 3.

Antimicrobial resistance patterns among the 822 staphylococci isolates using the VITEK2 system

	No. of isolates	CC-R & EM-R	CC-I or S				No. of isolates	CC-R & EM-R	CC-I or S
			EM-S	EM-R					EM-S	EM-R
			EM-S	ICR (+)	ICR (−)				EM-S	ICR (+)	ICR (−)
MRSA	345	250	39	52	4	MRCoNS	266	130	60	29	47
MSSA	156	5	125	21	5	MSCoNS	55	0	40	1	14
Total	501	255	164	73	9	Total	321	130	100	30	61

Abbreviations: MRSA, methicillin-resistant S. aureus; MSSA, methicillin-susceptible S. aureus; MRCoNS, methicillin-resistant coagulase-negative staphylococci; MSCoNS, methicillin-susceptible coagulase-negative staphylococci; CC, clindamycin; EM, erythromycin; S, susceptible; I, intermediate; R, resistant; ICR, inducible clindamycin resistance.

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