Fungal chitosan was extracted from Aspergillus niger mycelia. The produced chitosan was characterized with deacetylation degree of 89.2%, a molecular weight of 2.4 × 104？Da, and 96.0% solubility in 1% acetic acid solution. The antibacterial activity of fungal chitosan was evaluated against two foodborne pathogens, that is, Salmonella typhimurium and Staphylococcus aureus, using the established antibacterial assays, for example, zone of growth inhibition and agar plat count tests, and using 2,3,5,-triphenyltetrazolium chloride (TTC) as chromogenic marker for qualitative and quantitative determining of antibacterial potentiality. The TTC (0.5% w/v) was added, at concentration of 10%, to cultured broth, containing chitosan with different concentrations then the formed formazan was separated. The formation of red formazan could be considered as a qualitative indication for antibacterial activity, whereas the measurement of color intensity for the resuspended red formazan, using spectrophotometer at 480？nm, provided a quantitative evidence for the strength of the used antibacterial agent. Regarding the rapidity, technical simplicity, and cost-effectiveness, TTC assay could be recommended as an efficient alternative method for qualitative and quantitative determination of chitosan antibacterial activity and could be suggested for general evaluation of antibacterial agents. 1. Introduction Chitosan is a cationic polysaccharide consisted of many monosaccharide units of β-(1,4) linked 2-amino-2-deoxy-D-glucopyranose. The innocuous biodegradable and bioeffective nature of chitosan recommends its use in many fields of biotechnology, food industry, cosmetology, agriculture, and pharmacology [1–3]. Chitosan can be extracted from the cell wall of fungi, particularly zygomycetes. The production of chitosan from fungal cell walls has many advantages such as independence of seasonal factor and wide-scale production. The extraction process is more simple and cheap resulting in a reduction in time and cost required for production [4]. The antimicrobial materials are widely used in industry, community, and private settings to prevent microbial infection and contamination. To obtain biocidal effect without releasing biocides into the environment, natural antimicrobials, like chitosan, are highly recommended to be applied. The antimicrobial activity of chitosan is a hot research topic and there are several articles dealing with it and its derivatives [2, 3, 5–7]. Moreover, chitosan has numerous advantages over other chemical disinfectants since it possesses a stronger
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