Biofilm Formation of Multidrug-Resistant MRSA Strains Isolated from Different Types of Human Infections.

Vanessa Silva,Luciana Almeida,Manuela Caniça,Patrícia Poeta,José L Capelo,Vânia Gaio,Nuno Cerca,Vera Manageiro,Gilberto Igrejas

doi:10.3390/pathogens10080970

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the main pathogens causing chronic infections, mainly due to its capacity to form biofilms. However, the mechanisms underlying the biofilm formation of MRSA strains from different types of human infections are not fully understood. MRSA strains isolated from distinct human infections were characterized aiming to determine their biofilm-forming capacity, the biofilm resistance to conventional antibiotics and the prevalence of biofilm-related genes, including, icaA, icaB, icaC, icaD, fnbA, fnbB, clfA, clfB, cna, eno, ebpS, fib and bbp. Eighty-three clinical MRSA strains recovered from bacteremia episodes, osteomyelitis and diabetic foot ulcers were used. The biofilm-forming capacity was evaluated by the microtiter biofilm assay and the biofilm structure was analyzed via confocal scanning laser microscopy. The antimicrobial susceptibility of 24-h-old biofilms was assessed against three antibiotics and the biomass reduction was measured. The metabolic activity of biofilms was evaluated by the XTT assay. The presence of biofilm-related genes was investigated by whole-genome sequencing and by PCR. Despite different intensities, all strains showed the capacity to form biofilms. Most strains had also a large number of biofilm-related genes. However, strains isolated from osteomyelitis showed a lower capacity to form biofilms and also a lower prevalence of biofilm-associated genes. There was a significant reduction in the biofilm biomass of some strains tested against antibiotics. Our results provide important information on the biofilm-forming capacity of clinical MRSA strains, which may be essential to understand the influence of different types of infections on biofilm production and chronic infections.

Highlights

Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of communityand hospital-associated infections
The biofilm production of osteomyelitis strains was significantly lower than the biofilm production of strains isolated from other infections (p < 0.001)
Since the variation of only one or two biofilm-related genes may induce more or less biofilm production, we studied the prevalence of 13 genes involved in biofilm production, icaA, icaB, icaC, icaD, fnbA, fnbB, clfA, clfB, cna, eno, ebpS, fib and bbp, performed by PCR

Summary

Introduction

Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of communityand hospital-associated infections. In the European Union (EU) and the European Economic Area (EEA), MRSA accounts for approximately 150,000 of hospital-associated infections each year, resulting in more than 7000 deaths and a socioeconomic burden of EUR 380 million annually [5,6]. The incidence of MRSA infections in the EU and EEA varies significantly between the north and south, with southern countries reporting above-median MRSA proportions [7]. A decrease in the weighted proportion of MRSA among S. aureus isolates from 2007 to 2015 was reported, a study by Cassini et al (2019) showed that the estimated incidence of MRSA infections increased 1.28-fold [6].

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