Journal List > Korean J Clin Microbiol > v.13(4) > 1038200

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

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.

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.
kjcm-13-157f1.tif
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
ICR (+) ICR (−) 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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