# Effects of Chitosan Coatings on Controlling
## 4 Discussion  
As asserted in the Introduction, the objective here was to investigate the antimicrobial activity of chitosan against pathogenic bacteria--specifically, _L. monocytogenes_ and both sensitive and methicillin-resistant _S. aureus_--in beef and mutton packaging. The available literature suggests a variety of mechanisms regarding the antimicrobial activity of chitosan, without a consensus or clarity as to the mode of action [2,21]. Three mechanisms are most likely involved: The first is based on the cationic properties of chitosan. The positively charged amino groups of chitosan interact with the negatively charged cell membranes of microbes, leading to the disruption of the membrane barrier, leakage of intracellular contents, and cell death [15]. The second mechanism involves the chelating characteristics of chitosan, since chitosan is able to bind selectively with metals and block the active centers of various enzymes of the microbial cell, thereby inhibiting the microbial metabolism and growth [2]. The third mechanism is based on the molecular weight of chitosan, where chitosan of high molecular weight forms an impermeable polymeric layer on the surface of microbial cells, blocking the entry of nutrients to the cell and the excretion of toxic compounds [22]. On the other hand, chitosan of low molecular weight is able to enter the microbial cell and bind with the microbial DNA, leading to alterations in the transcription and translation of the DNA [15]. Regardless of the involved mechanism, chitosan exhibits a wide range of antimicrobial activity, including against Gram-positive and Gram-negative bacteria, fungi, and yeasts, targeting the cell membrane [2,15]. Given the antimicrobial properties that chitosan exhibits in laboratory experiments, several researchers have focused on the application of chitosan membranes in food systems, including meat products. Chitosan can enhance the quality and shelf life of meat products, including chicken fillets, pork sausages, beef slices, and mutton pieces [23, 24, 25, 26], as well as fish products such as rainbow trout [27]. In addition to spoilage microorganisms, chitosan coatings are also effective in controlling the growth of pathogenic bacteria in meat products. [PERSON] et al. [28] prepared beef samples that were coated with 1% chitosan emulsions, and reported that chitosan reduced the viable _Salmonella_ Typhimurium and _Escherichia coli_ by about 90% compared to the initial inoculum. Similar results were also observed by [PERSON] et al. [29] and [PERSON] et al. [30], whereas [PERSON] et al. [31] reported antimicrobial activity of chitosan against _E. coli_ O157:H7 in beef--especially when combined with liposome-encapsulated phages. [PERSON] et al. [32] also stated that 3% chitosan reduced the spore germination and outgrowth of _Clostridium perfringens_ by 2 log\({}_{10}\) CFU/g in ground beef. Regarding mutton, [PERSON] et al. [33] reported that chitosan films (2%) eliminated fecal  
Figure 2: _L. monocytogenes_ populations during the storage of beef (**a**) or mutton (**b**) under refrigeration for 21 days. coliforms and inhibited the growth of _Bacillus cereus_ and _Pseudomonas fluorescens_ in ready-to-eat mutation seekh kababs. This is consistent with the findings of [PERSON] et al. [34] and [PERSON] et al. [23], who reported antimicrobial activity of chitosan against a wide range of Gram-positive and Gram-negative bacteria, including _Salmonella_ Enteritidis, _Pseudomonas aeruginosa_, and lactic acid bacteria. In our study, chitosan coatings reduced the concentrations of _S. aureus_ in beef and mutton pieces by approximately 1.5 log\({}_{10}\) CFU/g. This is consistent with the findings of [PERSON] and [PERSON] [35], who reported that chitosan membranes (2%) and vacuum-packaging reduced the staphylococcal concentrations in beef pieces by around 2 log\({}_{10}\) CFU/g. However, [PERSON] et al. [36] observed a 6-log decrease in staphylococcal concentrations in beef that was coated with 2% chitosan solution.