The effect of N-acetylcysteine in a combined antibiofilm treatment against antibiotic-resistant Staphylococcus aureus

Abstract

Background The WHO declared Staphylococcus aureus as a ‘pathogen of high importance’ in 2017. One-fifth of all bloodstream-related infections in Australia and 12 000 cases of bacteraemia in the UK (2017–18) were caused by the MRSA variant. To address the need for novel therapies, we investigated several permutations of an innovative combination therapy containing N-acetylcysteine (NAC), an antibiotic and an enzyme of choice in eradicating MRSA and MSSA biofilms. Methods Biofilm viability (resazurin assay) and colony count methods were used to investigate the effect of NAC, antibiotics and enzymes on S. aureus biofilm disruption and killing. The effects of NAC and enzymes on the polysaccharide content of biofilm matrices were analysed using the phenol/sulphuric acid method and the effect of NAC on DNA cleavage was determined using the Qubit fluorometer technique. Changes in biofilm architecture when subjected to NAC and enzymes were visualized using confocal laser scanning microscopy (CLSM). Results NAC alone displayed bacteriostatic effects when tested on planktonic bacterial growth. Combination treatments containing 30 mM NAC resulted in ≥90% disruption of biofilms across all MRSA and MSSA strains with a 2–3 log10 decrease in cfu/mL in treated biofilms. CLSM showed that NAC treatment drastically disrupted S. aureus biofilm architecture. There was also reduced polysaccharide production in MRSA biofilms in the presence of NAC. Conclusions Our results indicate that inclusion of NAC in a combination treatment is a promising strategy for S. aureus biofilm eradication. The intrinsic acidity of NAC was identified as key to maximum biofilm disruption and degradation of matrix components.

N-Acetylcysteine Protects Bladder Epithelial Cells from Bacterial Invasion and Displays Antibiofilm Activity against Urinary Tract Bacterial Pathogens

“…This study also showed that NAC degraded secreted and matrix-bound polysaccharides in a strain-dependent manner in the uropathogens tested. This finding has also been observed in other biofilm-forming pathogens, such as S. aureus MSSA and MRSA, P. aeruginosa , and Helicobacter pylori [ 32 , 45 , 46 ]. Degrading polysaccharides required for matrix formation could affect the adhesive properties of the matrix to a surface and subsequent robust biofilm formation [ 36 ], the characteristics of which are especially vital for bacterial survival in the urinary tract given the shear stress bacteria are exposed to by urine flow forces [ 47 ].…”

“…The effect of NAC on the initial adhesion of UPEC and E. faecalis was investigated as mentioned previously [ 32 ]. Briefly, six-well plates (Corning Corp., Corning, NY, USA) were seeded with bacteria at a density of OD 600 nm = 0.1 ± 0.02 and incubated for 2 h at 37 °C and 100 rpm.…”

“…NAC acts as a potent antibiofilm agent alone and in combination with antibiotics such as fosfomycin and Augmentin against Staphylococcus aureus (methicillin-resistant and sensitive), E. coli , E. faecalis , P. aeruginosa, Burkholderia spp. , and other species, including surface-associated biofilms [ 18 , 32 , 33 , 34 ]. A recent insightful study showed that NAC penetrates the biofilm matrix and kills bacteria within, resulting in an empty gel-like matrix [ 35 ].…”

“…The researchers postulated that NAC destroys bacterial cells by dissociating and acidifying the bacterial cytoplasm, thereby causing protein and DNA degradation [ 35 ]. At lower concentrations of around 2 g/L, NAC alone can inhibit E. coli biofilm synthesis by 20–40% [ 18 ], and it can affect biofilm viability in S. aureus MRSA and MSSA by over 90% at concentrations of 4 g/L [ 32 ].…”

Current and Emerging Therapies to Combat Cystic Fibrosis Lung Infections

“…Recent in vitro studies of N-acetylcysteine efficacy on S. aureus biofilms of six MRSA and six MSSA isolates demonstrated that N-acetylcysteine is equally disruptive against Gram-positive organisms [ 149 ]. Addition of 30 mM N-acetylcysteine alone disrupted the biofilms of all 12 isolates by ≥90%, with a 2–3 log 10 decrease in CFU/mL.…”