Abstract
Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and minimum biofilm eradication concentration (MBEC) and kill kinetics were established for vancomycin, rifampicin, trimethoprim, gentamicin, and ciprofloxacin against the biofilm forming bacteria Staphylococcus epidermidis (ATCC 35984), Staphylococcus aureus (ATCC 29213), Methicillin Resistant Staphylococcus aureus (MRSA) (ATCC 43300), Pseudomonas aeruginosa (PAO1), and Escherichia coli (NCTC 8196). MICs and MBCs were determined via broth microdilution in 96‐well plates. MBECs were studied using the Calgary Biofilm Device. Values obtained were used to investigate the kill kinetics of conventional antimicrobials against a range of planktonic and biofilm microorganisms over a period of 24 hours. Planktonic kill kinetics were determined at 4xMIC and biofilm kill kinetics at relative MBECs. Susceptibility of microorganisms varied depending on antibiotic selected and phenotypic form of bacteria. Gram‐positive planktonic isolates were extremely susceptible to vancomycin (highest MBC: 7.81 mg L−1: methicillin sensitive and resistant S. aureus) but no MBEC value was obtained against all biofilm pathogens tested (up to 1000 mg L−1). Both gentamicin and ciprofloxacin displayed the broadest spectrum of activity with MIC and MBCs in the mg L−1 range against all planktonic isolates tested and MBEC values obtained against all but S. epidermidis (ATCC 35984) and MRSA (ATCC 43300).
Highlights
Medical device related infections present an increasing burden on health care systems with concomitant high rates of patient morbidity and mortality [1]
Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and minimum biofilm eradication concentration (MBEC) and kill kinetics were established for vancomycin, rifampicin, trimethoprim, gentamicin, and ciprofloxacin against the biofilm forming bacteria Staphylococcus epidermidis (ATCC 35984), Staphylococcus aureus (ATCC 29213), Methicillin Resistant Staphylococcus aureus (MRSA) (ATCC 43300), Pseudomonas aeruginosa (PAO1), and Escherichia coli (NCTC 8196)
None of the antimicrobials tested were fully microbicidal against all forms of Grampositive and Gram-negative microorganisms researched at the concentrations tested
Summary
Medical device related infections present an increasing burden on health care systems with concomitant high rates of patient morbidity and mortality [1]. Their increased clinical presentation and associated problems are due mainly to the ability of microorganisms to form resistant biofilms at the biomaterial surface. Biofilms are heterogeneous by nature and contain a subpopulation of dormant persister cells that show tolerance to treatment by standard antimicrobial regimens [2]. In order to be clinically successful in the treatment of a medical device infection, the antibiotic’s pharmacokinetic properties, rate of kill, and concentration must be assessed against a spectrum of relevant biofilm forming microorganisms. This study is set out to obtain an indication of the ability of currently prescribed antimicrobials to eradicate both planktonic and biofilm forms of these device related pathogens in vitro, with conclusions made to their relative success
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