Comparison of MIC with MBEC Assay for &amp;lt;i&amp;gt;in Vitro&amp;lt;/i&amp;gt; Antimicrobial Susceptibility Testing in Biofilm Forming Clinical Bacterial Isolates

Summaiya Mulla,Ambuj Kumar,Sangita Rajdev

doi:10.4236/aim.2016.62007

Abstract

Context: MIC results can be misleading for treatment of biofilm associated. The Minimum Biofilm Eradication Concentration (MBEC) measures the determination to be made for a biofilm susceptibility to antibiotics. Aims: Assessment of biofilm production and comparison of the MIC and MBEC assays evaluate differences in the antibiotic sensitivity patterns of different clinical bacterial isolates from patients implanted with medical devices. Settings and Design: Random sampling with experimental study at tertiary care institute. Methods and Material: The study was carried out during January 2014 to March 2014 on 50 positive bacteriological cultures of medical devices which were inserted in hospitalized patients. Biofilm forming strains were identified by tissue culture plate method & tube method. Biofilm-producing and non-biofilm forming reference strains were used as controls. Assay has been developed for the use with flat bottom, 96-well microtiter plates. Sterile autoclaved PCR tubes were used as pegs which provided surface for the biofilm formation. Amikacin, ciprofloxacin, trimethoprim-sulfamethoxazole, vancomycin, cefoperazone/ sulbactam, gentamycin were tested for MIC and MBEC assay. Statistical Analysis Used: Results will be discussed in the form of percentages. Results: Colonization by Klebsiella pneumoniae, Acinetobacter baumanni and Pseudomonas aeruginosa was prevalent bacterial isolates in medical devices. MBEC was higher for all the antibiotics as compared to MIC except amikacin MBEC for Pseudomonas was the same as MIC. Conclusions: Device associated bacterial biofilms are the major source of infections in patients of critical care setup. MIC misleads physician for organism’s drug susceptibility testing, which results in therapeutic failure. MBEC can guide regarding choice and proper dosing of antibiotics to be given. That’s why major studies for similar testing should be done with clinical evaluation.

Highlights

Medical devices are frequently inserted in ICU patients for various interventions and it’s in continuous contact with body fluids and irrigation fluids
Tissue culture plate method (TCP)/Microtitre plate method: Isolates were inoculated in tryptic soy broth (TSB) with 0.25% glucose; density was standardized by comparison with 0.5 McFarland standards (i.e. 108 CFU/ml) and incubated for 24 hour at 37 ̊C
Chart 2 showed the comparison between MIC and Minimum Biofilm Eradication Concentration (MBEC) value of various antibiotics like cefoperazone/ sulbactam, gentamycin, amikacin & ciprofloxacin

Summary

Introduction

Medical devices are frequently inserted in ICU patients for various interventions and it’s in continuous contact with body fluids and irrigation fluids If it gets implanted with bacteria it serves as an excellent surface for the formation of bacterial biofilms. Bacteria in biofilm community are generally highly drug resistant because of increased production of extracellular matrix, multi-layered colonies, decreased metabolic rates, decreased multiplication and polymicrobial colonization. It becomes good source of infection in patients with poor immunity with drug resistant bacteria. The Clinical Laboratory Standards Institute (CSLI) provides testing of bacteria in plantonic form and does not have method for antimicrobial susceptibility testing against biofilm associated organisms. Ceri et al developed the MBEC assay and used it to test several antimicrobial agents against biofilms [4] [5]

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