219. Anti-Biofilm Activity of N-Acetylcysteine as Demonstrated by Confocal Laser Scanning Microscopy
Session: Abstracts: Antibacterial Agents and Resistance
Friday, October 22, 2010
Background: Our goal was to study the effects of N-acetylcysteine (NAC) exposure on biofilm thickness, bacterial viability and polysaccharide content of clinically relevant bacterial biofilms.   

Methods: We grew, in tissue-culture wells, biofilms of the following organisms: methicillin-sensitive and –resistant Staphylococcus aureus (MSSA, MRSA), methicillin-resistant S. epidermidis (MRSE), vancomycin-resistant Enterococcus faecium (VRE), Pseudomonas aeruginosa, Enterobacter cloacae and Klebsiella pneumoniae. After 24 hours of incubation, the broth was replaced with either tryptic soy broth (TSB) containing NAC 80 mg/ml or TSB alone as control and then incubated for 24 hours. The wells were then rinsed and stained with propidium iodide (stains non-viable cells red) and FITC-labelled concanavalin A type IV (stains extracellular polysaccharide green). Using an upright confocal laser scanning microscope, five non-contiguous areas were viewed in each well. Each experiment was conducted thrice. We measured biofilm thickness, counted the number of non-viable bacterial cells, and measured green fluorescent intensity as a marker of extracellular polysaccharide in the biofilm matrix. All continuous variables were analyzed using a t-test.

Results: We noted statistically significant decrease in biofilm thickness of NAC-treated wells for all organisms (p<0.05) except VRE. We also noted an increase in the number of non-viable cells in the NAC-treated wells of gram-positive organisms. This was statistically significant for MRSA, MRSE, and VRE, with a trend for higher number of non-viable cells for MSSA. We noted scant cellularity in the NAC-treated gram-negative biofilms which also lacked complex 3-dimensional structures that were characteristic of the controls. Green fluorescent intensity was similar in the control and experimental arms.

Conclusion: NAC exposure leads to disruption of clinically relevant and drug-resistant bacterial biofilms. This involves increased cell death of biofilm-embedded gram-positive bacteria as well as disruption of complex structures. Polysaccharide content of the residual biofilm appears unchanged. NAC has the potential for use as a novel anti-infective agent for control of biofilm-related infections.

Subject Category: A. Antimicrobial agents and Resistance

Saima Aslam, MD , Med.; Div. of Infectious Diseases, Baylor College of Medicine, Houston, TX
Rabih O. Darouiche , Veteran Affairs Medical Center, Houston, TX


S. Aslam, None

R. O. Darouiche, Yes
Baylor Coll. of Medicine (BCM): BCM owns the rights to a patent describing the use of N-acetylcysteine to combat device-related infections based on my invention. There is no licensing agreement regarding this patent between BCM and any company and hence no royalties. and Employee,

Findings in the abstracts are embargoed until 12:01 a.m. EST Thursday, Oct. 21 with the exception of research findings presented at IDSA press conferences.


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