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

Adilson De Oliveira,Katheryne Benini Martins,Danilo Moraes Riboli,Luiza Pinheiro,Valéria Cataneli Pereira,Maria Ribeiro De Souza Da Cunha

doi:10.3390/ijms17091423

Adilson De Oliveira, Katheryne Benini Martins + Show 4 more

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https://doi.org/10.3390/ijms17091423

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Abstract

The objective of the present study was to determine the antimicrobial resistance profile of planktonic and biofilm cells of Staphylococcus aureus and coagulase-negative staphylococci (CoNS). 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 submitted to 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). 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. These isolates were evaluated regarding their resistance profile. Determination of planktonic cell MIC identified three (21.4%) S. aureus strains that were resistant to oxacillin and six (42.8%) that were resistant to erythromycin. Among the CoNS, 31 (88.6%) strains were resistant to oxacillin, 14 (40%) to erythromycin, 18 (51.4%) to gentamicin, and 8 (22.8%) to sulfamethoxazole/trimethoprim. None of the planktonic isolates were resistant to vancomycin or linezolid. MICs were 2-, 4-, 8-, and up to 16-fold higher for biofilm cells than for planktonic cells. This observation was more common 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. The results showed considerably higher MICs for S. aureus and CoNS biofilm cells 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. Linezolid was the most effective drug in inhibiting staphylococci in the biofilm, without an increase in the MIC, when compared to planktonic cells. None of the isolates were resistant to this drug.

Highlights

Staphylococcus aureus and Staphylococcus epidermidis are common causative agents of infections associated with medical devices such as vascular catheters, prostheses, and artificial heart valves because of their capacity to adhere to the smooth surface of these materials and to form a biofilm [1]
The use of antibiotics for the routine treatment of staphylococcal infections is generally able to eliminate planktonic cells, while biofilm cells can spread further even when treatment is interrupted since they remain protected from the action of the antimicrobial agents and from the host’s immune system [9]
A major issue in the antimicrobial resistance of staphylococci are oxacillin-resistant S. aureus because these microorganisms are generally resistant to multiple drugs and because of the large number of strains found

Summary

Introduction

Staphylococcus aureus and Staphylococcus epidermidis are common causative agents of infections associated with medical devices such as vascular catheters, prostheses, and artificial heart valves because of their capacity to adhere to the smooth surface of these materials and to form a biofilm [1]. In addition to S. epidermidis, other coagulase-negative staphylococci (CoNS) such as S. hominis, Int. J.

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