## 4 Discussion
Interestingly, the strains typed as 1/2b and 4b were more potent biofilm producers than strains of other serotypes, and most of the biofilm-producing strains were isolated from environmental samples, a breaking point for possible food contamination. Conversely, [PERSON] et al. [60], who collected samples from a fish processing environment in Japan, observed that strains belonging to serotypes 1/2a and 1/2c formed stronger biofilms than strains belonging to serotypes 3a and 3b. In the present study, all _Listeria monocytogenes_ strains possessed the infectivity genes _inLA_, _inIC_, _inIB_, _inI_, _actA_, _hhyA_, _iup_, _plcA_, and _prfA_, except for one strain lacking the _hhyA_ gene and one strain lacking the _iup_ gene. The results of this study agree with the results of similar studies. [PERSON] et al. [40] reported that all strains from fresh fish and environmental samples possessed all the infectious genes examined (_inLA_, _inIC_, _inIB_, _inI_, _actA_, _hhyA_, _iup_, _plcA_, and _prfA_). Similarly, [PERSON] and [PERSON] [41] reported that all strains collected from fresh fish samples in India had _plcA_, _prfA_, _actA_, _hhyA_, and _iup_ genes, although no attempt was made to detect _inLA_, _inIC_, _inIB_, and _inI_ genes. In addition, similar results were reported by [PERSON] et al. [50], where all strains isolated from fresh fish, shrimp, and ready-to-eat seafood had _inLA_, _inIC_, _inI_, and _hhyA_ genes. [PERSON] and [PERSON] (2017) reported that all 57 strains from fresh and smoked fish samples in Poland possessed all 10 genes tested (_inLA_, _inIB_, _inIC_, _inI_, _lmo2672_, _plcA_, _plcB_, _hhyA_, _actA_, and _mpl_). Although certain serotypes have been involved more frequently in human listeriosis cases, it seems that most if not all _Listeria monocytogenes_ have the genetic background to cause disease, given the opportunity. Possible affinities between _Listeria monocytogenes_ strains were performed by analyzing and comparing the protein profiles of the strains using MALDI-TOF. Two different clusters were identified. In cluster A, a high degree of affinity was observed between strains recovered exclusively from fish samples, although these were not from the same species of fish. The cluster A strains probably originated from points of contamination prior to the fishmonger's shop since no strain belonging to this group was found in the shops' environmental samples. The exact source, though, is difficult to assess and can include several points in the seafood production chain, including fishing, fishing boats, and processing [40]. In cluster B, a greater affinity was observed between the strains, which have been recovered from both fish and the environment (cutting board and ice). These strains can circulate between fish and the environment, with the source of contamination not being clear, since the surface may be contaminated by the raw material (fish) and in turn re-contaminate fish, or the other way round. It was interesting, however, that a certain strain was recovered from the ice used to chill fish. Ice was sampled directly from the fish box; therefore, it is not clear if it was contaminated during production or not. Nevertheless, ice can subsequently further contaminate both fish stored in it and the fishmonger's environment, either directly through the melted water or indirectly through fish. Also, during fish cleaning, droplets and scales may be thrown into the fish-processing area, potentially contaminating various parts of the fish market, including the fish and the ice. In conclusion, two main routesof contamination were identified, one involving mostly fish and the second implying the cyclic contamination of both the fish and the fishmonger's environment. In the second cluster, specific characteristics of the strains, such as their ability to form biofilms, are of importance to the persistence of the strains. Similar affinities between the strains have been reported by [PERSON] et al.