Comparison of three standardized disc susceptibility testing methods for colistin

Tan, Thean Yen; Ng, Lily Siew Yong

doi:10.1093/jac/dkl330

Cited by 82 publications

(79 citation statements)

References 7 publications

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“…In the current study the disc diffusion although showing CA of 93% yet it failed to detect the two resistant A. baumanniii detected by the broth microdilution (reference method) giving VMEs, however, basing our findings on only these resistant strains is inconclusive but in the absence of verified guidelines, disc diffusion method should not be used alone in judging colistin susceptibility in A. baumanniii. Our finding is supported by others who reported disc diffusion to be an unreliable method for detecting polymyxins susceptibility [16] [27]. As regards Vitek 2 AST, we found it to be reliable and easy with 100% CA, Lee et al 2013 tested 213 isolates, including 13 colistin resistant Acinetobacter strains.…”

Section: Discussionsupporting

confidence: 86%

In Vitro Activity of Colistin and Vancomycin or Azithromycin Combinations on Extensively Drug Resistant Acinetobacter baumannii Clinical Isolates

Okasha¹,

Meheissen²

2017

AiM

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Background: Extensively drug resistant Acinetobacter baumannii (XDR-AB) presents an increasing challenge to health care in Egypt as they are among the most common bacteria isolated in hospital setting. Treatment of such infections usually involves the use of antimicrobial agents in combination. Various combinations have been proposed, with colistin serving as the backbone in many of them even for colistin resistant isolates. Aim: The study was conducted in order to test the in vitro combined effects of colistin and vancomycin or azithromycin against (XDR-AB) causing infections at Alexandria Main University Hospital in Egypt, in an attempt to detect the possibility of a beneficial combination therapy. Material/Methods: Thirty XDR-AB clinical isolates were included in the study. Antibiotic susceptibility testing was performed using automated Vitek 2 compact system and disc diffusion method. Colistin antibiotic disc diffusion test was compared with broth microdilution method. Organisms were also tested against colistin and vancomycin or azithromycin in combination using checkerboard synergy test and FICI (Fractional Inhibitory Concentration Index) was calculated. Synergy was defined as a FICI of ≤0.5. Results: On comparing the two methods used to detect susceptibility to colistin to broth microdilution for MIC (minimum inhibitory concentration) determination, as a reference method, the Vitek showed 100% categorical agreement (CA), on the other hand, the disc diffusion showed CA of 93% with very major errors. Synergy was detected for all isolates (100%) when combining colistin with vancomycin (FICI mean = 0.08). As for azithromycin, 21 strains had FICI range from 0.7 to 1.001, denoting indifference; the remaining 9 strains showed synergy with FICI range from 0.06 to 0.241. The mean colistin/azithromycin FICI was 0.71 for the 30 isolates. Conclusion: These findings suggest that regimens containing vancomycin may confer therapeutic benefit for infection due to XDR-AB; however, other methods (time-kill assay) should be used to confirm such synergy. Furthermore, the optimal combination treatment for serious XDR-AB infection should be addressed in a prospective clinical trial.

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Section: Discussionsupporting

confidence: 86%

In Vitro Activity of Colistin and Vancomycin or Azithromycin Combinations on Extensively Drug Resistant Acinetobacter baumannii Clinical Isolates

Okasha¹,

Meheissen²

2017

AiM

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“…Considerable variations exist regarding the species and selection criteria used, zone diameter breakpoints, and MIC susceptibility breakpoints. Several recent and older studies have found very major error rates of ϳ5% to 20% (isolates falsely identified as being susceptible) and have concluded that disk diffusion testing is unreliable (4,55,83,86,111,116,130,146,167,179). Therefore, despite the inclusion of disk diffusion testing guidelines by several groups, the accumulated data suggest that alternative methods should be used for susceptibility testing of polymyxins.…”

Section: Susceptibility Testing Methodologymentioning

confidence: 99%

Polymyxins Revisited

et al. 2008

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SUMMARY The global emergence of multidrug-resistant gram-negative bacilli has spurred a renewed interest in polymyxins. Once discarded due to concerns regarding nephrotoxicity and neurotoxicity, polymyxins now hold an important role in the antibiotic armamentarium. However, more reliable information is needed to determine the optimal dosing of these agents. Also, unanswered questions regarding in vitro testing remain, including questions regarding the reliability of automated systems and the establishment of appropriate breakpoints for defining susceptibility. Most contemporary clinical studies examining the use of these agents have involved patients with infections due to multidrug-resistant Pseudomonas aeruginosa and Acinetobacter baumannii strains. It has been reassuring that polymyxin therapy for resistant bacteria has resulted in clinical responses and toxicity rates similar to those for carbapenem therapy for susceptible isolates. While most surveillance studies demonstrated high rates of susceptibility, several reports noted the emergence of polymyxin-resistant nosocomial pathogens. Polymyxins have assumed an important antibiotic niche for therapy for hospital-acquired infections; further studies defining the optimal use of these agents will likely extend the duration of their clinical usefulness.

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“…The disc diffusion technique was reported to be an unreliable method for evaluating the susceptibility of bacteria to polymyxins because these antibiotics diffuse poorly in agar. Consequently results of polymyxin disk diffusion tests should be confirmed with a broth dilution method [14,15].…”

Section: Antimicrobial Resistancementioning

confidence: 99%

Acinetobacter species meningitis in children: a case series from Karachi, Pakistan

Saleem

Shah

Shaikh

et al. 2011

J Infect Dev Ctries

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Introduction: Multidrug-resistant strains of Acinetobacter pose a serious therapeutic dilemma in hospital practice, particularly when they cause meningitis, as the few antimicrobial agents to which these isolates are susceptible have poor central nervous system (CNS) penetration. Methodology: We retrospectively reviewed the clinical course and outcome of eight consecutive cases of meningitis due to Acinetobacter spp. in children ages 15 years or less, seen in a tertiary care medical center in Karachi, Pakistan. Results: Of the eight cases of Acinetobacter meningitis, isolates from five patients were pan-resistant, and two were multidrug-resistant. A neurosurgical procedure was performed in five of eight patients followed by external ventricular drain insertion prior to the development of infection. Seven received intravenous (IV) polymyxin (mean; 12.8 days), while 5/8 also received intrathecal (IT) polymyxin (mean; 12.0 days). The mean length of hospitalization was 38.7 ± 19 days. All patients achieved cerebrospinal fluid (CSF) culture negativity by the end of treatment (mean; 5.4 days). Two patients died: one with pan-resistant Acinetobacter, and the second with a multi-drug resistant isolate. Conclusion: Post-neurosurgical multidrug-resistant and pan-resistant Acinetobacter meningitis can be successfully treated if appropriate antimicrobial therapy is instituted early. The role of IT polymyxin B administration alone versus combination therapy (IV and IT) needs further study.

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Comparison of three standardized disc susceptibility testing methods for colistin

Abstract: Disc susceptibility testing methods are unreliable at detecting colistin resistance. Dilution methods should be the method of choice for susceptibility testing of colistin.

Cited by 82 publications

References 7 publications

<i>In Vitro</i> Activity of Colistin and Vancomycin or Azithromycin Combinations on Extensively Drug Resistant <i>Acinetobacter baumannii</i> Clinical Isolates

<i>In Vitro</i> Activity of Colistin and Vancomycin or Azithromycin Combinations on Extensively Drug Resistant <i>Acinetobacter baumannii</i> Clinical Isolates

Polymyxins Revisited

Acinetobacter species meningitis in children: a case series from Karachi, Pakistan

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Comparison of three standardized disc susceptibility testing methods for colistin

Abstract: Disc susceptibility testing methods are unreliable at detecting colistin resistance. Dilution methods should be the method of choice for susceptibility testing of colistin.

Cited by 82 publications

References 7 publications

&lt;i&gt;In Vitro&lt;/i&gt; Activity of Colistin and Vancomycin or Azithromycin Combinations on Extensively Drug Resistant &lt;i&gt;Acinetobacter baumannii&lt;/i&gt; Clinical Isolates

&lt;i&gt;In Vitro&lt;/i&gt; Activity of Colistin and Vancomycin or Azithromycin Combinations on Extensively Drug Resistant &lt;i&gt;Acinetobacter baumannii&lt;/i&gt; Clinical Isolates

Polymyxins Revisited

Acinetobacter species meningitis in children: a case series from Karachi, Pakistan

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Product

Resources

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<i>In Vitro</i> Activity of Colistin and Vancomycin or Azithromycin Combinations on Extensively Drug Resistant <i>Acinetobacter baumannii</i> Clinical Isolates

<i>In Vitro</i> Activity of Colistin and Vancomycin or Azithromycin Combinations on Extensively Drug Resistant <i>Acinetobacter baumannii</i> Clinical Isolates