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CORRESPONDENCE
Year : 2013  |  Volume : 31  |  Issue : 2  |  Page : 207-208
 

Importance of performing routine quality control testing of antimicrobial discs


Department of Medical Microbiology, Post Graduate Institute of Medical Education and Research, Chandigarh, India

Date of Submission18-Apr-2013
Date of Acceptance26-May-2013
Date of Web Publication19-Jul-2013

Correspondence Address:
P Ray
Department of Medical Microbiology, Post Graduate Institute of Medical Education and Research, Chandigarh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0255-0857.115244

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How to cite this article:
Arora S, Gautam V, Ray P. Importance of performing routine quality control testing of antimicrobial discs. Indian J Med Microbiol 2013;31:207-8

How to cite this URL:
Arora S, Gautam V, Ray P. Importance of performing routine quality control testing of antimicrobial discs. Indian J Med Microbiol [serial online] 2013 [cited 2019 Oct 16];31:207-8. Available from: http://www.ijmm.org/text.asp?2013/31/2/207/115244


Dear Editor,

Resistance to antibiotics among bacteria is increasing throughout the world due to their overuse. Thus, it becomes important for microbiologists to provide clinicians accurate information regarding susceptibility pattern so that appropriate antibiotic can be selected, thereby preventing emergence of resistance. [1] Because of its simplicity and rapidity, Kirby-Bauer disc diffusion (KBDD) is most widely used method for susceptibility testing in microbiology laboratories. [2] Apart from storage and handling, the results obtained from disc diffusion method depend upon the quality of antibiotic discs.

As a part of routine quality control, we tested imipenem (10 μg) discs (HiMedia Lot No. 126990 11-2011), which are routinely used in our laboratory, on both ATCC Pseudomonas aeruginosa 27853 and clinical Acinetobacter isolates. The results were cross checked using Becton Dickinson and Company, USA (BD) imipenem discs and Bio Merieux SA, France, imipenem E-strips (0.002-32 μg/ml). The same 0.5 McFarland inoculum of ATCC P. aeruginosa was used on unsupplemented Mueller Hinton Agar (MHA) medium for testing 11 discs, out of which, 9 showed zone diameters out of quality control range (20-28 mm), while the results of BD discs and E-strips were within the quality control range. The results obtained by using 26 clinical Acinetobacter isolates are shown in [Table 1]. Taking MIC values obtained by E-strips as the standard, BD discs did not show any discrepancy, while 80.8% (21/26) of HiMedia discs showed false susceptible results. This might be due to the higher content of the antibiotic used to compensate for the loss during transportation and storage. The comparison between the two is shown in [Figure 1].
Table 1: Comparison of results obtained using two different sources of discs and E-test

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Figure 1: The same isolate resistant with BD discs (B) and one HiMedia disc (H), while false susceptible with another

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However, satisfactory results were obtained with newer lot of the same antibiotic, suggesting the need of quality control testing of discs every time a new lot is introduced in the laboratory, as the zone of inhibition is very important in labelling an isolate as sensitive or resistant, and the interpretation directly affects the choice of therapy.

 
 ~ References Top

1.Cantón R, Loza E, Del Carmen Conejo M, Baquero F, Martínez-Martínez L; MENSURA Collaborative Group. Quality control for beta-lactam susceptibility testing with a well-defined collection of enterobacteriaceae and pseudomonas aeruginosa strains in Spain. J Clin Microbiol 2003;41:1912-8.  Back to cited text no. 1
    
2.Bauer AW, Kirby WM, Sherris JC, Turck M. Antibiotic susceptibility testing by a standardized single disk method. Am J Clin Pathol 1966;45:493-6.  Back to cited text no. 2
    


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