|Year : 2017 | Volume
| Issue : 2 | Page : 317
Inconsistency in disk diffusion while testing carbapenems in Chryseobacterium spp.
Vivek Hada, Anuradha Sharma
Department of Microbiology, All India Institute of Medical Sciences, Jodhpur, Rajasthan, India
|Date of Web Publication||5-Jul-2017|
Department of Microbiology, All India Institute of Medical Sciences, Jodhpur, Rajasthan
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Hada V, Sharma A. Inconsistency in disk diffusion while testing carbapenems in Chryseobacterium spp. Indian J Med Microbiol 2017;35:317
|How to cite this URL:|
Hada V, Sharma A. Inconsistency in disk diffusion while testing carbapenems in Chryseobacterium spp. Indian J Med Microbiol [serial online] 2017 [cited 2017 Sep 26];35:317. Available from: http://www.ijmm.org/text.asp?2017/35/2/317/209582
We read with interest the article “noncatheter-related bacteraemia due to Chryseobacterium indologenes in an immunocompetent patient” by Baruah et al. in the current issue of the Indian Journal of Medical Microbiology. The authors have done the antimicrobial susceptibility using disk diffusion testing. Similarly, in a case of isolation Chryseobacterium spp. from pyonephrosis and urinary tract infection, disk diffusion was done for antimicrobial susceptibility., The disk diffusion method is not the reliable method for testing in Chryseobacterium spp. Furthermore, there are no breakpoints mentioned for Chryseobacterium spp. in Clinical and Laboratory Standards Institute guidelines and it currently does not recommend the disk diffusion testing for these organisms.
Recently in our laboratory, Department of Microbiology, All India Institute of Medical Sciences, Jodhpur, two isolates of Chryseobacterium spp. were isolated from a patient suffering from suspected aspiration pneumonia and admitted in the Intensive Care Unit of our hospital. The Chryseobacterium spp. was isolated from the bronchial aspirate and blood culture of the patient. Both the isolates shared the same biochemical properties and were identified as Chryseobacterium spp. (Elizabethkingia meningosepticum) on the basis of conventional biochemical reactions. While antimicrobial susceptibility was evaluated, it was seen that both the isolates had minimum inhibitory concentration (MIC) >32 mg/l for imipenem using E-test but on disk diffusion the imipenem disk had a zone size of 20 mm [Figure 1]. Similar observations were noted with cotrimoxazole and meropenem as the results were compared with MICs in Vitek 2 which showed MIC of 80 mg/l and >16 mg/l, respectively, although both drugs showed diameter of zone of inhibition >20 mm.
|Figure 1: Disk diffusion test of the isolate showing zone size of 20 mm around imipenem disk (Left). No zone of inhibition with minimum inhibitory concentration >32 mg/l during the E-test (Right).|
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The complete lack of zone on E-test and the presence of zone in disk diffusion test with same carbapenem highlight the inability of disk diffusion test in identifying the resistance in this organism which can lead to false interpretation. Thus, whenever we are dealing with these organisms, disk diffusion test should be avoided. There is a need for guidelines on identification and susceptibility testing of nonfermenters other than Pseudomonas and Acinetobacter due to their growing surge.
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| ~ References|| |
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