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LETTER TO EDITOR  
Year : 2014  |  Volume : 57  |  Issue : 3  |  Page : 518-519
Comparison of Clinical and Laboratory Standards Institute 2008 and 2010 guidelines in interpreting susceptibility of enterobacteriaceae isolates


Department of Microbiology, Indira Gandhi Government Medical College, Nagpur, Maharashtra, India

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Date of Web Publication14-Aug-2014
 

How to cite this article:
Agrawal GN, Shevade SU. Comparison of Clinical and Laboratory Standards Institute 2008 and 2010 guidelines in interpreting susceptibility of enterobacteriaceae isolates. Indian J Pathol Microbiol 2014;57:518-9

How to cite this URL:
Agrawal GN, Shevade SU. Comparison of Clinical and Laboratory Standards Institute 2008 and 2010 guidelines in interpreting susceptibility of enterobacteriaceae isolates. Indian J Pathol Microbiol [serial online] 2014 [cited 2020 May 29];57:518-9. Available from: http://www.ijpmonline.org/text.asp?2014/57/3/518/138818


Editor,

Members of enterobacteriaceae family are the most frequently encountered bacterial isolates recovered from clinical specimens. Among them, extended spectrum β-lactamase (ESBL) and AmpC β-lactamase (AmpC) production have been increasingly reported worldwide. [1] AmpC producing strains may appear susceptible to a particular β-lactam antibiotic in vitro, but show no clinical response when used to treat serious infections. [2] Clinical and Laboratory Standards Institute (CLSI) 2008 Guidelines [3] states that enterobacteriaceae strains should be screened for ESBL production. On the contrary, CLSI 2010 guidelines [4] states that ESBL testing is no longer necessary before reporting the results. This is because CLSI 2010 has sufficiently modified breakpoints of zone diameters and minimum inhibitory concentration (MIC) of β-lactam antibiotics, which had been continued in CLSI 2011 [5] and 2012 guidelines [6] (zone diameters and MIC of carbapenems were again modified in CLSI 2011 guidelines). Both CLSI 2008 and CLSI 2010 guidelines do not comment on the AmpC testing. Unlike CLSI 2008, CLSI 2010 has mentioned test for suspected carbapenemase production in enterobacteriaceae isolates and added that the testing is not necessary and is useful for epidemiological purposes.

For the interpretation of sensitivity of enterobacteriaceae isolates for β-lactam antibiotics, CLSI 2010 differs with CLSI 2008 in zone sizes of only aztreonam and third generation cephalosporins, i.e., cefotaxime (CTX), ceftriaxone, ceftazidime, ceftizoxime. [3],[4] Furthermore, they differ widely in interpreting susceptibility of these antibiotics by MIC. In this study, we have chosen CTX as a representative of third generation cephalosporins. Hence, the study was attempted to compare antibiotic susceptibility of enterobacteriaceae isolates by CLSI 2008 and CLSI 2010 for third generation cephalosporins.

Three hundred enterobacteriaceae strains were subjected to antibiotic susceptibility testing to CTX by disk diffusion and MIC testing. The production of ESBL (by screening and phenotypic confirmatory test), [3],[4] AmpC (by cefoxitin-CTX disk antagonism test) [7] and carbapenemase (by screening and phenotypic confirmatory test) [4] were tested in the enterobacteriaceae isolates. Of 300 strains, 111 ESBL, 12 AmpC and 27 carbapenemase producers were detected. Co-production of β-lactamases was not seen.

Among 111 ESBL producers, 81 (72.97%) were resistant to CTX by both the guidelines, whereas remaining 30 (27.03%) were intermediate resistant by 2008 and resistant by 2010 guidelines. Therefore, additional testing for ESBL production was not found to be necessary.

Among 12 AmpC producers, 11 (91.67%) were intermediate resistant by 2008 and resistant by 2010 guidelines and 1 (8.33%) was susceptible by both the guidelines.

None of the 27 carbapenemase producers showed zone of inhibition. They showed high MIC value, i.e., >64 μg/ml.

Hence for interpretation of CTX susceptibility in enterobacteriaceae isolates, additional ESBL and carbapenemase testing is not needed for treatment purpose if we follow CLSI 2010 guidelines; although, ESBL testing was indicated for CLSI 2008 guidelines. Out of the 300 isolates, a single AmpC producer was missed. In this study, for AmpC production testing only cefoxitin-CTX disk antagonism test was used; cloxacillin and boronic acid inhibitor-based methods were not used. It is questionable whether to perform mass screening for AmpC production when chance of missing AmpC producers is low.

 
   References Top

1.
Pitout JD, Reisbig MD, Venter EC, Church DL, Hanson ND. Modification of the double-disk test for detection of Enterobacteriaceae producing extended-spectrum and AmpC beta-lactamases. J Clin Microbiol 2003;41:3933-5.  Back to cited text no. 1
    
2.
Cantarelli VV, Inamine E, Brodt TC, Secchi C, Cavalcante BC, Pereira Fde S. Utility of the ceftazidime-imipenem antagonism test (CIAT) to detect and confirm the presence of inducible AmpC beta-lactamases among Enterobacteriaceae. Braz J Infect Dis 2007;11:237-9.  Back to cited text no. 2
    
3.
Performance Standards for Antimicrobial Susceptibility Testing; Eighteenth Informational Supplement. Wayne, Pennsylvania, USA: CLSI; 2008.  Back to cited text no. 3
    
4.
Performance Standards for Antimicrobial Susceptibility Testing; Twentieth Informational Supplement. Wayne, Pennsylvania, USA: CLSI; 2010.  Back to cited text no. 4
    
5.
Performance Standards for Antimicrobial Susceptibility Testing; Twenty-First Informational Supplement. Wayne, Pennsylvania, USA: CLSI; 2011.  Back to cited text no. 5
    
6.
Performance Standards for Antimicrobial Susceptibility Testing; Twenty-Second Informational Supplement. Wayne, Pennsylvania, USA: CLSI; 2012.  Back to cited text no. 6
    
7.
Rodrigues C, Joshi P, Jani SH, Alphonse M, Radhakrishnan R, Mehta A. Detection of -Lactamases in nosocomial gram negative clinical isolates. Indian J Med Microbiol 2004;22:247-50.  Back to cited text no. 7
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Correspondence Address:
Gopal N Agrawal
Department of Microbiology,Indira Gandhi Government Medical College, Central Avenue, Nagpur, Maharashtra - 440018
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0377-4929.138818

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