# Effects of Chitosan Coatings on Controlling
## 4 Discussion
This difference can be attributed to the higher concentrations of chitosan solutions used and the use of only one strain of _S. aureus_, as opposed to the four strains that were used in our study, given that the strain used by [PERSON] et al. could have been more chitosan-sensitive. [PERSON] et al. [37] also reported that the staphylococcal concentrations gradually increased in minced beef samples coated with 1% chitosan emulsions, in contrast to the results of this study, possibly due to the fact that the minced meat was purchased from a local market with non-specified conditions concerning meat storage. In addition, shearing of minced meat can increase the area available for microbial growth [38] and, therefore, can have an impact on the proliferation of _S. aureus_. Regarding mutton, [PERSON] et al. [33] observed an immediate effect of chitosan coating (2%) in mutton seekh kababs, as it reduced staphylococcal concentrations by 2-3 log\({}_{10}\) CFU/g. [PERSON] et al. [39] also reported that the bactericidal effect of chitosan on minced lamb meat is concentration-dependent. In this study, no synergic effect of chitosan and vacuum-packaging on the staphylococcal counts was observed. The main mechanism of chitosan against _S. aureus_ is the formation of an impervious polymeric layer on the surface of microbial cells that inhibits the entrance of nutrients to the cells [23]; according to this mechanism, no complementarity exists between the effects of chitosan and vacuum-packaging; therefore, a synergistic effect is not possible. Concerning MRSA strains, [PERSON] et al. [40] examined the efficacy of chitosan against MRSA and its effect on the shelf life of pork; they reported that the combination of epicatechin gallate and chitosan extended the shelf life of pork from 5 to 7 d at 4 \({}^{\circ}\)C and from 36 h to 48 h at 25 \({}^{\circ}\)C. [PERSON] et al. [41] reported that chitosan reduced staphylrosanthin production and, therefore, reduced the virulence of MRSA. In addition, it asserted a dose-dependent effect on MRSA biofilms. Therefore, chitosan can be effective against MRSA isolates in a similar way as against the sensitive _S. aureus_ strains. This observation is consistent with the results of [PERSON] et al. [42], who reported that methicillin resistance did not affect the antimicrobial and anti-biofilm activities of chitosan. On the contrary, they argued that the coexistence of methicillin and chitosan can be complementary against MRSA, since both substances target the bacterial cell wall. Regarding _L. monocytogenes_, chitosan coatings reduced its concentrations in beef and mutton pieces by up to 2 log\({}_{10}\) CFU/g. This is consistent with the results of [PERSON] et al. [43], who also reported a 2-log\({}_{10}\) decrease in the counts of _L. monocytogenes_ on ready-to-eat bovine meatballs coated with 1% chitosan solution. [PERSON] et al. [44] coated bovine meat pate with chitosan at a concentration of 5 mg chitosan/g pate and observed an almost 4-log\({}_{10}\) decrease in the inoculated counts of _L. monocytogenes_ due to the antimicrobial activity of chitosan. The higher decrease observed may be because the meat pate was inoculated with only one strain of _L. monocytogenes_. According to [PERSON] et al. [45], chitosan emulsions with oregano oil were shown to reduce the _L. monocytogenes_ counts on beef tenderloin by up to 4 log\({}_{10}\) CFU/g. On the other hand, [PERSON] et al. [46] reported that the _L. monocytogenes_ counts of chitosan-coated (1%) beef samples gradually increased throughout the storage period, even though the counts were lower than those of the control samples. Similar results were also reported by [PERSON] et al. [47], who observed an increase in the counts of _L. monocytogenes_ in chitosan-coated (1%) roast beef, despite the initial decrease in the counts by up to 2 log\({}_{10}\) CFU/g after the application of the chitosan solution. Similar to _S. aureus_, no synergic effect of chitosan and vacuum-packaging was observed.