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Evaluation of the antimicrobial susceptibilities of coagulase-negative staphylococci by E-test
C Barelli1, E C Minto, R Martinez
1Department of Clinical, Toxicologic and Bromatologic Analyses, Faculty of Pharmaceutical Sciences of Ribeirão Preto, University of São Paulo, Brasil.
Abstract:
Coagulase-negative staphylococci (CoNS) have recently emerged as important nosocomial pathogens. In this study, the susceptibility of 53 isolates of CoNS (42 S. epidermidis, 6 S. haemolyticus, 3 S. caprae, 1 S. lugdunensis and 1 S. chromogenes) obtained over a 1 year period at a Brazilian Hospital were tested for vancomycin, teicoplanin, cephalothin, penicillin, oxacillin, and chloramphenicol. The minimal inhibitory concentration (MICs) were determined by the E-test using saturated swabs or the flooding method. No isolates showed resistance to vancomycin, 3 (5.7%) were resistant to teicoplanin, 5 (9.4%) to cephalotin, most of them, (47, 88.6%) were resistant to penicillin, 19 (35.8%) to oxacillin and 27 (50.9%) to chloramphenicol. The study shows that the increased resistance of CoNS can cause serious infections of difficult treatment. The E-test proved to be a convenient and reliable method for MIC determination of CoNS isolates and the qualitative and quantitative results obtained by flooding were much more reproducible than the results obtained using swabs.
Insights
Coagulase-negative staphylococci (CoNS) are increasingly causing hospital-acquired infections. This study found high resistance rates to common antibiotics like penicillin and chloramphenicol in CoNS isolates, highlighting treatment challenges.
Area of Science:
- Microbiology
- Infectious Diseases
- Clinical Pharmacy
Background:
- Coagulase-negative staphylococci (CoNS) are emerging as significant nosocomial pathogens.
- Understanding their antimicrobial susceptibility is crucial for effective treatment strategies.
Purpose of the Study:
- To assess the antimicrobial susceptibility patterns of CoNS isolates from a Brazilian hospital.
- To evaluate the efficacy of the E-test method for determining minimal inhibitory concentrations (MICs).
Main Methods:
- 53 CoNS isolates (including S. epidermidis, S. haemolyticus) were tested against vancomycin, teicoplanin, cephalothin, penicillin, oxacillin, and chloramphenicol.
- Minimal inhibitory concentrations (MICs) were determined using the E-test with saturated swabs and the flooding method.
Main Results:
- No vancomycin resistance was observed.
- Resistance rates were: teicoplanin (5.7%), cephalothin (9.4%), penicillin (88.6%), oxacillin (35.8%), and chloramphenicol (50.9%).
- The flooding method for E-test provided more reproducible MIC results than the swab method.
Conclusions:
- High levels of antibiotic resistance in CoNS underscore the difficulty in treating associated infections.
- The E-test is a reliable method for MIC determination of CoNS isolates.
- Antimicrobial stewardship programs are essential to combat rising CoNS resistance.