# Methicillin Resistance of Food-Borne Biofilm-Forming Staphylococcus-Crocei
## 4 Discussion
As already mentioned, the isolates used in this study were previously characterized in terms of their antibiotic resistance profile as having a high level of resistance to \(\beta\)-lactam and to non-\(\beta\)-lactam antibiotics (such as vancomycin, erythromycin, tetracycline, and trimethoprim/sulfamethoxazole) [12]. In the present work, the \(\beta\)-lactam antibiotic, methicillin, had MICs ranging from 1 ug/mL to over 32 ug/mL, with 13 of the 34 isolates having MICs greater than 4 ug/mL (38% of methicillin resistant isolates). In 20 of the 34 isolates, the MBC value was twice the MIC value. In fact, most antibiotics show this ratio between MBC and MIC [26]. Regarding the biofilms formed, it was not possible to determine the concentration of methicillin that promotes their removal. Several factors have been suggested to explain the extraordinary resistance of biofilm bacteria to antibiotics. Among them are the low metabolic rates and reduced growth rates exhibited by biofilm bacteria, particularly those in the innermost layers. All together with the activation of antibiotic resistance mechanisms can make biofilm cells between 10 and 1000 times more resistant than their planktonic counterparts [27; 28]. The gene that encodes resistance to methicillin resistance _mecA_ was previously identified in the _Staphylococcus_ isolates used in this study [12]. This gene is located in a mobile genetic element called SCCmec (staphylococcal cassette chromosome mec) and encodes a modified penicillin-binding protein called PBP2a or PBP2? (penicillin-binding protein 2a or 2-prime) [29]. The bacterial community of the biofilm can exhibit altered gene expression, including the _mecA_. This altered expression can lead to an increase in the production of resistance proteins such as PBP2a that deactivate or bind to antibiotics, reducing their effectiveness [30]. Consequently, even in the presence of high methicillin concentrations, the methicillin-resistant _S. aureus_ (MRSA) and the methicillin-resistant _Staphylococcus_ biofilm community in general can continue to synthesize their cell wall, which allows it to survive and reproduce. In this study, the maximum biofilm removal (reduction of 2 log CFU/cm\({}^{2}\)) was observed with 8 ug of methicillin/mL. The exception was the species _S. pasteuri_ (reduction of 1.5 log CFU/cm\({}^{2}\)), although this was one of the species that showed the highest susceptibility to methicillin (80% of the isolates with MIC = 4 ug/mL). These results suggest that the higher concentration of methicillin may limit its own penetration into the biofilm matrix. However, several authors [31; 32; 33; 34] have suggested that reduced penetration of antibiotics cannot fully explain the resistance of biofilms to antibiotics. Other mechanisms that may explain the resistance and tolerance of biofilms to antibiotics may be related to persistent cells and adaptive responses [35]. Antibiotics such as fluoroquinolones, rifampicin, and ampicillin have good penetration into the biofilm matrix, although they fail to eradicate bacteria from the biofilm (log reductions \(<\) 3 log CFU/cm\({}^{2}\)) [36]. Moreover, even in the case of compounds with low diffusion within biofilms, they all end up reaching the bacteria in the biofilm, although with different times of action and efficiencies [37]. [PERSON] et al. [38] suggested the use of a combination of several strategies for the management of _S. aureus_biofilms, including early physical removal of colonized materials or local administration of high doses of antibacterial chemotherapy. The occurrence of biofilm-forming strains in the food environment is of significant relevance, particularly when considering species that are multidrug-resistant, as was the case in this study. In the food environment, biofilms can develop on various equipment and surfaces, such as food processing machinery, utensils, and storage containers. These biofilms provide a favorable environment for the growth and survival of pathogenic bacteria, including _S. aureus_[35; 39].