Antimicrobial Resistance Profile of Planktonic and Biofilm Cells of Staphylococcus aureusand Coagulase-Negative Staphylococci

• Grant number: 16/17167-3
• Support Opportunities: Regular Research Grants - Publications - Scientific article
• Start date: October 01, 2016
• End date: March 31, 2017
• Field of knowledge: Biological Sciences - Microbiology - Biology and Physiology of Microorganisms
• Principal Investigator: Maria de Lourdes Ribeiro de Souza da Cunha
• Grantee: Maria de Lourdes Ribeiro de Souza da Cunha
• Host Institution: Instituto de Biociências (IBB). Universidade Estadual Paulista (UNESP). Campus de Botucatu. Botucatu , SP, Brazil

Abstract

Objectives: To determine the antimicrobial resistance profile of planktonic and biofilm cells of Staphylococcus aureus and coagulase-negative staphylococci (CoNS).Methods: Two hundred Staphylococcus spp. strains were studied, including 50 S. aureus and 150 CoNS strains (50 S. epidermidis, 20 S. haemolyticus, 20 S. warneri, 20 S. hominis, 20 S. lugdunensis, and 20 S. saprophyticus). Biofilm formation was investigated by adherence to polystyrene plates. Positive strains were analyzed by the broth microdilution method to determine the minimum inhibitory concentration (MIC) for planktonic and biofilm cells and the minimal bactericidal concentration for biofilm cells (MBCB).Results: Forty-nine Staphylococcus spp. strains (14 S. aureus, 13 S. epidermidis, 13 S. saprophyticus, 3 S. haemolyticus, 1 S. hominis, 3 S. warneri, and 2 S. lugdunensis) were biofilm producers and were used to evaluate the resistance profile. Determination of the MIC for planktonic cells revealed three (21.4%) S. aureus strains that were resistant to oxacillin and six (42.8%) resistant to erythromycin. Among CoNS, 31 (88.6%) strains were resistant to oxacillin, 14 (40%) to erythromycin, 18 (51.4%) to gentamicin, and eight (22.8%) to sulfamethoxazole/trimethoprim. None of the planktonic samples was resistant to vancomycin or linezolid. Biofilm cells exhibited two-, four-, eight- and up to 16-fold higher MICs than planktonic cells. This observation was more frequent for vancomycin and erythromycin. The MBCB ranged from 8 to >256 µg/ml for oxacillin, 128 to >128 µg/ml for vancomycin, 256 to >256 µg/ml for erythromycin and gentamicin, >64 µg/ml for linezolid, and 32/608 to >32/608 µg/ml for sulfamethoxazole/trimethoprim.Conclusions: The results showed a considerable increase in the MIC of S. aureus and CoNS biofilm cells when compared to planktonic cells. Analysis of MBCM confirmed that even high concentrations of vancomycin were unable to eliminate the biofilms of S. aureus and CoNS species. Among the antimicrobial drugs tested, linezolid exhibited the best performance in inhibiting staphylococci in the biofilm, without an increase in the MIC when compared to planktonic cells. None of the strains was resistant to this drug. (AU)