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Tolerance of Staphylococcus epidermidis grown from indwelling vascular catheters to antimicrobial agents
N Khardori1, M Yassien, K Wilson
1Department of Internal Medicine, Southern Illinois University School of Medicine, Springfield 62794-9230, USA.
Abstract:
During a prospective study of indwelling vascular catheter-related infections, 134 isolates of Staphylococcus epidermidis were grown from 700 catheter tips. In vitro antimicrobial susceptibility testing of these isolates to oxacillin, vancomycin and ofloxacin was performed using the standard broth microdilution technique. These results were compared to those for the same organisms grown in biofilm before the addition of antimicrobial agents. In 96-well flat bottom microtiter plates, 10(4)-10(5) colony forming units of S. epidermidis in 0.1 ml broth were grown for 18 h at 37 degrees C, at which time a biofilm was observed for all isolates. Different concentrations of antimicrobial agents (0.1 ml) were then added to the plates. The plates were incubated for 18 h at 37 degrees C. Since MICs could not be estimated in these plates, all the wells were subcultured after mixing the biofilm with the broth. Minimum bactericidal concentrations (MBCs) were defined as 99.9% reduction in colony forming units. For organisms grown in suspension, 100% of the isolates were susceptible to vancomycin, 81% to ofloxacin and 40% to oxacillin. MBCs of susceptible isolates were within four-fold differences for vancomycin (53%), oxacillin (50%), and ofloxacin (51%). When grown as a biofilm, 78%, 93% and 71% of isolates had MBCs of > or = 2048 micrograms ml-1 of oxacillin, vancomycin and ofloxacin respectively. These data demonstrate the reduced bactericidal activity of antimicrobial agents against S. epidermidis in a biofilm and a simple method for its detection in the microbiology laboratory.
Insights
Antimicrobial resistance in Staphylococcus epidermidis biofilms significantly reduces treatment effectiveness. This study demonstrates reduced bactericidal activity against S. epidermidis grown in biofilm, highlighting the need for effective biofilm detection methods.
Area of Science:
- Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Catheter-related infections are a significant concern in healthcare settings.
- Staphylococcus epidermidis is a common cause of these infections, often forming biofilms.
- Biofilm formation can lead to increased antimicrobial tolerance and treatment failure.
Purpose of the Study:
- To evaluate the in vitro antimicrobial susceptibility of Staphylococcus epidermidis isolates from catheter tips.
- To compare the efficacy of oxacillin, vancomycin, and ofloxacin against S. epidermidis in planktonic versus biofilm states.
- To assess a simple method for detecting antimicrobial activity against S. epidermidis biofilms.
Main Methods:
- Prospective study of 134 Staphylococcus epidermidis isolates from 700 catheter tips.
- Standard broth microdilution for in vitro antimicrobial susceptibility testing.
- Comparison of Minimum Bactericidal Concentrations (MBCs) for planktonic and biofilm-grown organisms.
Main Results:
- In suspension, 100% of isolates were susceptible to vancomycin, 81% to ofloxacin, and 40% to oxacillin.
- Biofilm formation drastically reduced susceptibility, with high MBCs (> or = 2048 µg/mL) for oxacillin (78%), vancomycin (93%), and ofloxacin (71%).
- MBCs showed within four-fold differences for susceptible planktonic isolates.
Conclusions:
- Antimicrobial agents exhibit significantly reduced bactericidal activity against Staphylococcus epidermidis when grown in a biofilm.
- Biofilm formation confers substantial tolerance to common antibiotics.
- A simple method for detecting antimicrobial activity against biofilms in the microbiology laboratory was demonstrated.